Mitch Chubb, a teacher, asks:
I'm currently reading A Beak of Finch. There is a passage referring to two different species of finches mating and having viable offspring. The passage continues discussing other hybrids that occur, ligers, mallards and pintails breeding, and mules. I was under the impression that hybrids such as mules did not occur naturally, rather mated artificially by man. Could you clarify this for me?
Richard Lampe, a biologist, replies:
The biological species concept uses
reproductive isolation as its emphasis in identifying the taxon known as
species. Useful as it may be in most situation, it is not without its problems.
Some organisms have not yet sufficiently diverged genetically to cause a loss of
reproductive fitness when they breed with "the other kind". When this happens,
there can be an exchange of genetic material across a zone where organisms of
two insipient species encounter each other. This can occur naturally but when it
does, the two different populations are likely to be quite similar
morphologically and hence genetically.
In other situations where this reproductive isolation
has been caused by an ecological barrier (for example, one group has adapted for
marsh and the second for forest), if these two habitats are brought into contact
then the organisms within them face the chance of making an improper mating
decision. This happens especially where human intervention has caused habitats
to shift or where species from vastly different regions are introduced to each
other. Though it's not perfect, Ernst Mayr's biological species concept
seems to provide biologists with a sound working definition of what is happening
in nature.
Hope that this helps.
Johnny, a grade school student, asks:
Can one really see steam? What I mean to say is, when one boils water doesn't the vaporization happen, which is invisible to us? So the "white cloud" or whatever it is we see coming up and off of the result, then, would just be condensation?
Jon Hutchins, a chemist, replies:
You are correct! One cannot see pure steam as it is a colorless gas. The cloudy appearance of steam is due to light diffraction by tiny water droplets suspended in the steam.
Shaun Ng, a middle school student, asks:
Is it possible to safely mutate anybody so that he/she could achieve positive results like growing wings, growing bigger, getting superhuman strength? And how is a person mutated?
Brian A. Lenzmeier, a biologist, replies:
As of now there is not a safe way to specifically mutate a human being to achieve some of the phenotypic descriptions you have given. Exposures to mutagens like radiation that might give you the results you seek will also mutate the rest of the genes and will cause a lot of damage to the person, even perhaps killing them.
There have been experiments using viruses to try to replace defective genes in people who have diseases, but those experiments have not been overly successful.
Your question also raises an important ethical dilemma. I don't think that as a society we would accept mutating human beings. Just think if you made the mutations you suggested in your best friend or mother or father and it ended up killing them. The risks are too great to justify experimenting in this manner on humans.
Neil Jones, a high school student, asks:
I am currently studying in the UK and need to complete an assignment to demonstrate that a non-toxic chemical substance can change colour over a period of days. Do you have any ideas/suggestions from which I can use as the basis of my experiment and develop to meet the requirements of the assignment?
Jon Hutchins, a chemist, replies:
I would suggest a very weak base (like sodium bicarbonate solution at pH about 8) in water, plus an indicator which changes colour at pH about 6-7. Leave out in a beaker exposed to air. It will pick up C02 and become more acid (pH about 5). If it goes too fast, add more bicarb.
A middle school student asks:
Is Leukemia the opposite of AIDS/HIV? Because AIDS is when you don't have enough working white blood cells to fight off diseases and germs, but Leukemia is when you have too many white blood cells?
Dr. Brian Lenzmeier, a biologist, replies:
Your explanation of Leukemia being the opposite of AIDS is a very good way to explain the two diseases and understand the immune system.
AIDS is caused by a virus called Human Immunodeficiency Virus, or HIV. HIV infects (gets inside) and kills your white blood cells, leaving you unable to fight off any infections by other bacteria and viruses and causing you to have AIDS.
Leukemia is a cancer where your
white blood cells gain the ability to divide uncontrollably and your body cannot
control their growth, leading to so many white blood cells that your body gets
overwhelmed.
Excellent observations!
Sabrina, a high school student, asks:
I'm doing an experiment on reaction times between sight and sound. Can you please tell me which of the two travels faster to the brain to send a reaction to a part of the body? And could you also explain why one is faster that the other?
Dr. Bob Ferguson, a psychologist, replies:
That's an interesting question, and one that is surprisingly complex to answer.
The main problem is that there are several different components that go into determining even a "simple" reaction time response. Here is an excellent web page that details these components: http://www.visualexpert.com/Resources/reactiontime.html The specific component that you have asked about is the neural conduction time from the eye to the primary visual cortex in the occipital lobe or from the ear to the corresponding auditory cortex in the temporal lobe. Since these distances are approximately the same, the difference in conduction times should be minimal.
Nonetheless, most researchers find that, overall, auditory RT's are SLIGHTLY faster than visual. These differences are small (on the order of 10-20 msec) and so can only be identified by calculating averages over large numbers of trials. Some typical data are available at: http://www.euronet.nl/users/fepsy/reac.htm
Since neural conduction times should not play a role here, the differences must be elsewhere. My guess is that the processing of the two types of signals by the cortex is where the difference lies (visual processing may be more complex and thus slower than auditory) but that is only a hypothesis. Another possibility is that once the cortex has recognized the signal, it simply takes longer for the visual cortex to initiate the motor response. But in either case, the time it takes the sensory signal to reach the brain is not likely the culprit.
Before finishing, you should know one last thing. RTs will change depending on the loudness of the tone or the brightness of the light...louder and brighter is faster. Maybe the aud/vis difference just reflects intensity differences of the stimuli used in the two parts of the experiment.
Told ya it was more complicated than you'd think!
Shay, a high school student, asks:
What are the generally excepted requirements an item needs
to have to be
considered alive?
Dr. James Eliason, a biologist, replies:
This question is a profound one and surprisingly difficult
to answer in
a way that covers all the possibilities. The following definition works
most of the time:
Something is considered alive if it could have done in the past, or can
do now, or should be able to do in the future, all of the following
"life processes".
Growth: it gets bigger and more complex with time.
Metabolism: It uses up energy to convert molecules to other molecules
and obtains energy in a similar way.
It absorbs material from its environment.
It excretes wastes to its environment.
It reproduces, makes more of its own kind.
It responds to its environment.
It adapts, changes its own structure in response to changes in the
environment.
It exhibits homeostasis, that is it maintains some properties of itself
constant despite changes in the environment.
It transports materials from one part of itself to another.
Some, but not all, living things move.
Some, but not all, living things senesce, that is show aging.
Over the course of generations, living organisms evolve.
Not all of these processes have to be present at the same time, but in
general at least one of them should always be present, probably the most
important being metabolism. For example, a young child cannot
reproduce, but is alive since he/she will be able to after reaching
adulthood. An old woman past menopause can no longer reproduce but is
alive since she could in the past. Grass is alive since it shows all
the life processes. Astroturf is not alive since it never reproduces.
Fire exhibits almost all life processes but is not alive since it does
not evolve.
Traditionally a person "died" when transport stopped, that is when the
heart stopped and blood stopped flowing, but this is no longer used
since in many cases the heart can be restarted and life continued. In
some cases death is taken to be when the person stops responding to the
environment, that is when the brain ceases function and cannot be
restarted. Determining the instant of death of a person is very
difficult. It depends on which life process(es) are required to be
present and on what scale. Hours after a person is declared dead many
of the person's cells function essentially normally even though the
whole person can never recover. It may be in the future that a person
is only truly dead if no cells remain "alive" and the person can no
longer be cloned!
Rick Lampe, a biologist, replies:
Hickman, Roberts and Larson (Integrated Principles of Zoology, 2001) answer this question by saying that living systems have a unique chemical organization, unique hierarchical organization, reproduction, genetic programs that enable fidelity in inheritance yet make it possible to change, a characteristic life cycle and the ability to interact with their environment.
Maleki Ray, a high school student, asks:
I'm trying to see if sound waves created by a computer (monotonous ring) could be redirected/misdirected/etc. by using wind created by fans (the purpose is to see if wind could misdirect sound waves). The fans would be lined up on one side of the testing area while a row of microphones aligned perpendicular to the fans record the sounds. The recordings are then placed into a program in the computer which displays the frequency and its value in decibels. I'm just trying to figure out if this is a logical experiment at all, and if using fans is the correct way to provide the interference necessary to answer my question. If there is another way to do this experiment by using different equipment or using a different setup please let me know. Any and all advice would be greatly appreciated.
Joe Traylor, a physicist, replies:
Malek, you pose a very interesting experiment! Yes, I recommend you try to do it. A couple of suggestions: make the source sound a pulse instead of continuous tone for part of the experiment. Then, you might try to see if there is a time delay for sound moving through wind as compared to that in more steady air. Questions to investigate: Does wind affect the velocity of sound? The frequency of sound? The loudness (amplitude) of sound? And, is moving into the wind different from moving with the wind, although these may be harder to do experimentally with fans and mics. The real underlying question is this: Does motion of the molecules in a medium affect the travel of waves in that medium? While I think there may be theoretical answers to those questions, it will be fun for you to investigate. Go for it!
PS. If you're looking for books on sound, check out the new 2002 3rd edition of The Science of Sound by Rossing, Moore, and Wheeler from Addison-Wesley. Pg. 53 talks about your subject.
Tom Hendricks, a microbiologist, asks:
A colleague of mine and I have a
dispute about designing experiments. He states that if you are just looking for
main effects, it is just as good to change one variable at a time as it is to
run a factorial experiment. I believe that the factorial experiment will give
you the main effects cleared of interactions, in other words the effect is valid
at multiple levels of the other factors. Who is correct?
Bob Blodgett, a psychologist, replies:
The issue, it seems to me, is
related to the analysis issue of experimentwise error that accrues from doing
individual tests each of which is evaluated for significance at 5%. That is the
design and analysis problem that the factorial design addresses with the
understanding that there are limitations on the number of factors that should be
used for sheer comprehensibility of the design. If multiple, single variable
experiments are conducted to test the same hypothesis, the potential for error
in the experimental procedures is increased in the same manner as is
experimentwise error in analysis. If we consider the potential for error in the
experimental procedures is compounded by experimentwise error in analysis, the
probability of a type-1 error increases dramatically. Consider the errors that
occur in replications (which is encouraged far too little by journal editors
these days) of experiments that yield different levels of significance in
analysis. Of course replications of experiments has different scientific
implications than does multiple experiments testing the same hypothesis. In
short, don't do it! Use the factorial design. That's my two cents worth of
advice for the day.
Harry Shingleton, a parent, asks:
I have children in secondary school
but have had a wholly classics education (which may explain my appalling
keyboard skill which cramps my style as you will quickly find out). I find
though that my son (aged 12) has a promising mathematical mind and a potential
for complex math. We frequently discuss astronomy and science subjects and I
wish to encourage him to a higher level of insight.
Shawn Stone, a physicist, replies:
We describe quantities in the universe with units. For instance, 3 meters for distance (m), 10 kilograms for mass (kg), and 5 seconds for time (s). The units for energy (e) are called the Joule which in these fundamental units 1 Joule= 1 (kg*m^2)/(s^2). The speed of light is a constant c= 3X10^8 m/s. The equivalence of mass and energy is some what of a misstatement since they do not have the same units. To make them equal we need a factor of c^2. This makes the units of e=mc^2 match up (both sides have (kg*m^2)/(s^2)). That answers the c^2 question as far as why it must be c^2 arithmetically.
The physical reasons for e=mc^2 are much more complex. It boils down to what two people observe when they are moving relative to each other. As an example, a person is on the ground (not moving relative to the ground) is watching a person in a train passing by at some constant speed. The person in the train drops a ball. Both people observe the ball falling, but both would describe what is happening a little bit differently. The person on the train sees the ball fall in a straight line, the person on the ground sees the ball move in an arc with the train. Even though they describe the motion differently both must agree that the laws of physics are obeyed. Using there observations they both can describe where the ball is and how fast it is moving relative to them. And they both would be correct. Where relativity really comes in is when the train is moving at speeds near c. Since the physics must be the same for both observers the speed of light must be c for both observers. Then when we consider what energy the person on the train measures the ball to have vs what energy the person on the ground measures the ball to have we come up with e=mc^2 (from the math it is like a proportionality constant). This is very general and glosses over a lot. But I hope this may help a little.
Dana asks:
A friend of mine says that a glass of soda sitting on a table in warm weather actually gets cooler through condensation on the glass. So lets say the the glass of soda is at +3 degrees C and the temperature of the air is +30 degrees C. Will the glass of soda become cooler for any period of time? I say no. Can you answer this for me please. Thank You.
Steve Tonsfeldt, a physicist, replies:
Your question was whether a glass of soda sitting on a table in warm weather actually gets cooler through condensation on the glass. You are correct and your friend is wrong. If your friend were right, such a process would violate the second law of thermodynamics and in the vast realm of experience, no violation has ever been seen. Condensation releases heat when it occurs, so it goes the other way. Evaporation is a cooling process, so that if the glass were surrounded by a damp cover, like some canteens are, evaporation of water cools the canteen. Dogs panting and people sweating are similar examples.
Roger Durham, a grade school student, asks:
How do sharks smell underwater without water going up their noses?
Carolyn Ashbaugh, a biologist, replies:
Sharks need to get water
"up their noses" in order to "smell". Sharks can
detect tiny quantities of substances in the water, but only if the substance
comes in contact with special chemosensory structures which are located in
something similar to a "nose". The "nose" of a shark
is not used for breathing, so it is not like getting water up your nose when you
go swimming. Human noses are good at (but not nearly so good as a dog's
nose) detecting chemicals or aromas (smells) in air.
A shark is not obtaining oxygen through its "nose"; instead, it takes
oxygen from the water using its gills (which are completely separate from its
"nose"). The air around us is approximately 20% oxygen. Oxygen
in oceans and lakes is usually measured in parts per million. There is
very little molecular oxygen in water when compared to air, and fish obtain
oxygen very differently from air breathing creatures. A shark uses its
"nose" for detecting chemicals (or substances like blood) which may
mean that a meal is nearby; it uses its gills for taking in oxygen.
Jono, a high school student, asks:
If you were traveling at the speed of light carrying a flash light and turned it on what would happen to the light coming out of the flashlight?
Steve Tonsfeldt, a physicist, replies:
Your question is a classic, in that it is exactly the question Einstein himself asked. The answer is not a common sense thing however. The answer is that in your reference frame you still measure the light to proceed away from you at c, 300 million meters per second. ALL OBSERVERS in so-called inertial reference frames, which are those moving at constant speeds with respect to each other, all measure the light to be moving at speed c. Since speed c is distance divided by time, that means that every one of these reference frames will measure different lengths and time intervals, all of which is called the special theory of relativity. The truth of the constancy of the speed of light has been experimentally checked by many experiments, originally by the Michelson-Morley experiment and the anti-common-sense result has been confirmed over and over again. You might want to look in the library for some physics books that go into this in more detail. Happy learning!
James, a middle school student, asks:
Why does a salt water solution take longer to freeze than a sugar water solution or plain tap water? When I tried this experiment the salt separated from the water but the sugar stayed dissolved. Why didn't it separate? I have looked under water soluble solutions but I can't find the answer?
Steve Tonsfeldt, a physicist, replies:
Your chemistry question is a good one and the answer depends on what the chemists call colligative properties, or properties that depend mostly on the ratio of the number of solute particles (sugar molecules or sodium and chlorine ions) to the number of solvent particles (water), and NOT on the particular chemical identity of the solute (whether it is sugar, salt or whatever). For your situation involving the freezing of the solutions of salt (NaCl) and sugar, consider what the water molecules have to do, in order to bond together in that hexagonal pattern that we see so well in snowflakes. The molecules of sugar get in the way to delay this happening and we get a certain amount of freezing temperature lowering, compared to plain tap water. With salt, the Na and Cl detach and become ions and you have TWICE as many obstacles for the water molecules to overcome, compared to the case for sugar. Therefore the freezing point depression for ordinary salt will be twice that for the same concentration or molarity of sugar solution. I would say that the ability to visualize things on the molecular level is a skill worth cultivating and that starts by asking good questions such as you have!
Michelle, a high school student, asks:
I
am starting an experiment this year in my school's research program and I have a
few questions that I hope you can help me with. I am going to have four groups
of rats: Group "A" will be put into a stimulating environment- a lot
of colorful toys, and things to climb on and play with. Group "B" will
also be stimulated, but they will be older than group "A". Group
"C" will be younger, but they will not be stimulated. Group
"D" will be older and not stimulated. To find out if the stimulated
groups are better learners, I will have them run through a maze and time them.
The faster times will be the smarter rats.
Here are my questions: 1. How many rats should I have
in each group? (I was thinking three) 2. How many times should I run them
through the maze? I know I would have to do it several times to see if the rats
learn where to go, but I do not know how soon and how often.
Jeanne Tinsley, an experimental psychologist, replies:
This sounds like a very interesting project which you are beginning. I will try to answer your questions. 1. You should try to have 5 or 6 rats in each group. Many experiments will use as many as 10 in a group. For your young rats, you should place them in the stimulating environment as soon as they are weaned. 2. How long it takes the rats to learn the maze will depend on how complicated the maze is. You could set a fairly long period of time for a trial and remove the rat after the time is finished – whether the animal has reached the end of the maze or not. You want to keep running them through the maze in a series of timed trials until they have learned it very well. You could set a criterion for this –perhaps 5 consecutive trials less than a particular time(probably just a few seconds). Your rats will need a reason to travel through the maze quickly. One of the easiest ways is to make them hungry and give them a very small food reward at the end of the maze. An easy way to make the rats hungry without hurting them is to feed them as much as they want to eat for one hour after you have run them through the maze. Then remove all of the food. Make sure the rats have water available at all times. Then the next day when you are ready to run the rats through the maze again, they will not have eaten for 23 hours and will be hungry. They will be motivated by the small food reward at the end of the maze. If you are going to run each rat in a block of trials each day (lets say 5), you need to be certain that the food reward is fairly small so the rat’s appetite is not satisfied. Noyes pellets work will for this. Good luck with your project.
Tessa, a middle school student, asks:
Why can you only see the red dust around the moon when there is a lunar eclipse? Why is the dust a red color when there is a lunar eclipse? Can there be other colors then red in the dust around the moon when there is a lunar eclipse? What would happen if some astronauts went up a few days before a lunar eclipse and waited? What would they see and would they see the red dust?
Shawn Stone, a physicist, replies:
The moon is not red because of dust during a lunar
eclipse. In fact, the dust of the moon is quite gray all the time!
Brenda Jennings, a parent, asks:
What is the definition of a true amphibian? Would a frog still be classified as an amphibian since it loses its ability to breathe in water as an adult? And if so, how would a frog be classified?
Rick Lampe, a biologist, replies:
Yes, frogs are amphibians. They spend part of their life in a stage that is totally in water and a second stage in which they are able to live on land. However, this second stage is still tied closely to the availability of water. The outer covering of amphibians in quite pervious to water and thus an amphibian can dry out quickly if it does not protect itself. There are three major grouping within the class Amphibia. One is the grouping including frogs and toads. Another includes salamanders and the third is a lesser known group consisting of a legless organism that lives in tropical soils. It's called the caecilian and is quite unusual.
Chris, a high school student, asks:
In Young's Double-Slit Experiment, it was shown that bright and dark bands were formed on a screen after passing through the double slits. We know that light is not a continuous wave, but rather made up of photons. Why do some photons go one way while the other photons move in a different direction?
Steve Tonsfeldt, a physicist, replies:
You have asked an excellent question that many other people have come up with. Richard Feynman once said something to the effect that the double slit experiment contains the fundamental mystery of quantum mechanics.
The first point to make is that our concepts of wave and particle are somewhat contradictory (complementary, as we say in physics). A particle is a point, just like you were told in geometry, but it has no dimensions! Awful hard to make a period for this sentence with no dimensions. On the other hand, an example of a perfect wave is y = sin kx, a pattern that extends from minus infinity to plus infinity. Again, it's hard to imagine any real object that can do that. So we need both particle and wave properties to describe real-world things and events.
The essential thing about light is that it travels like a wave and hits like a particle. So in transit the light wave passes through essentially both slits and yet when it comes to the screen, a tiny spot is made as a record of the detection of a photon or particle. This experiment has been done many times with extremely low intensity light and the researchers have seen the interference or diffraction pattern build up slowly, spot by spot, impact by impact.
Such behavior violates our so-called common sense, yet we must remember that our language and concepts reflect our experience in the macroscopic, everyday world and maybe should not be expected to apply to other realms of investigation. That's why experiments are so valuable in physics. We ask nature itself how it operates.
I hope this discussion helps. Please feel free to get back in touch. There are many excellent little books to read more about this topic.
Crystal M., a high school student, asks:
We were going over intermolecular forces in chemistry and my teacher mentioned the London Dispersion Forces. The question is, what is the reasoning behind why they are named the "London" dispersion forces?
Jon Hutchins, a physicist, replies:
London dispersion forces, the weakest type of Van der Waal's forces between atoms or molecules, were described using quantum mechanics by physicist F. (Frank?) London, I would guess about 1930.
Brenda, a high school student, asks:
Why does hammering on a magnetized rod make the rod lose its magnetism?
Steve Tonsfeldt, a physicist, replies:
Hello Brenda! Your question is a good one and it
might be good to look up a photomicrograph of a ferromagnet in order to see the
microscopic crystalline structure. Ferromagnets can be iron, steel, magnetite,
cobalt, etc. and are all characterized by the existence of magnetic domains,
little islands of order, in which tremendous numbers of atoms have their spins
aligned in the same direction. Knowing that current loops are the cause of
magnetism, that makes each domain a little magnet in its own right. If the iron,
for example is unmagnetized, all of these little domain magnets are randomly
oriented and cancel each other out. If there are more pointing in one direction
than the other, then it is a "permanent" magnet. However these little
magnets can be randomized by either hammering on the magnet or by heating the
magnet above a characteristic temperature called the Curie temperature (after
Pierre Curie, the researcher). For iron this is 770 deg. C.
Magnetism is a fascinating subject and I hope you look
up more on magnetic domains and ferromagnetism in particular. Enjoy!
Teresa Nichols asks:
Here is the problem. I understand that TMG(trimethylglycine) is Betaine, and the HCL supplement is Betaine HCL. How much betaine does TMG contain? Are there other things related to it---like Hydrochloride? How much betaine is in a betaine HCL 10 grain capsule? What are the equivalencies between the two?
Jon Hutchins, a physicist, replies:
According to the Merck index, betaine has a FW = 117.15, and the HCl compound has a FW = 36.5 higher, or 153.65, so 117g of betaine or 154g of betaine.HCl contain about the same amount of stuff. The grain is about 64.8 milligrams.
Shirley
, a parent, asks:
I need to find out what you would mix with baby oil to color it...I have a
project that I need to use oil to preserve the object...Now I need to have a way
to color it, but with what? If I use food coloring it beads up, if I use oil
based paint, a settlement settles to the bottom, not staying mixed, &
becomes cloudy, unless I used the wrong proportions.
Dennis Dykema, professor of art, replies:
Your question is a bit of a
puzzler. I can understand why food coloring wouldn't work as it is a dye in a
water based liquid. Of course it will bead up in an oil based liquid. Other
colorants like oil based paints achieve their color by the dispersion of finely
ground solid pigments. These, as you've noted tend to settle because they are
heavier than the oil, and occlude the clarity of oil because of their opacity.
I
remain a bit puzzled by your question, but suspect that you might have the best
luck if you seek out someone who specializes in fiberglass fabrication. Such a
manufacturer might be able to steer you to the dyes which are used to color the
two-part resins which are the basis for fiberglass. You may remember 30 years
ago or so, that craft stores sold kits which could be used to make clusters of
plastic grapes or plums. These kits included dyes which were mixed into the
resin along with the catalytic hardener. I think that sort of things has gone
out of style, (thankfully), but I'm sure some major craft suppliers might be
able to provide you with these dyes.
Andrea, a high school student, asks:
I'm a sophomore in an honors chemistry class. I was doing some lab work on the molar volume of hydrogen gas for a project. My partner and I had a lot of trouble completing the lab work, but we finished it except for a section on the Ideal Gas Laws. We were wondering if there was a chance that gases may not be ideal at low temperatures or high pressures. I think that they might be but I'm not quite sure and she also had no idea! I was wondering if you could help explain this to me?
Steve Tonsfeldt, a physicist, replies:
You are 100% correct in your suspicion that the ideal gas law breaks down for
low temperatures and/or high pressures. Let's go back to the three assumptions
for the ideal gas model.
1. The gas is assumed to
be composed of individual particles (atoms or molecules) whose actual dimensions
are small in comparison to the distances between them. (Note that this
assumption gets progressively worse as pressure increases or temperature
decreases - the atoms or molecules get closer together.)
2. These particles are in
constant motion and therefore have kinetic energy.
3. Neither attractive nor
repulsive forces exist between the particles. (This one is violated big-time at
low temperatures because many gases liquify, which means that the attractive
force between the atoms or molecules wins out over the random or thermal energy.
Also, at high pressures for any gas, there will be enough repulsive collisions
between the atoms or molecules that will modify the pressure.)
Physicists and chemists
describe the deviation from ideal behavior in tables or graphs of the
compressibilty or compression factor Z, which is defined as PV/nRT (= 1.00 for
ideal gas) and usually plot Z versus P, the pressure that is measured
experimentally. The net result to remember is that the product PV does not have
the same value for all gases, nor is the pressure dependence the same for
different gases, because the interatomic or intermolecular forces will be
slightly different. Nevertheless, the ideal gas law is a good first
approximation if the conditions are not too extreme.
Heather, a high school student, asks:
If I'm looking at a plant and see that it's green, I know that I see it as green because it contains chlorophyll, a pigment that is green because it absorbs all wavelengths of the visible light spectrum except green, which it doesn't absorb well--am I right? Well, what is it that causes chlorophyll not to absorb green light? And if I see all other colors because they absorb every color in the visible light spectrum except that which I see, what is it that enables them to absorb those particular colors? In other words, why are things good at observing certain wavelengths of light while reflecting and transmitting others?
Joe Traylor, a physicist, replies:
First of all, the color you see is a combination of MANY colors. The eye is an
"integrating device." That is, it combines its response to all the
wavelengths of light into one sum response called color. Thus, the green from
the plant really has MANY colors which your eye interprets as "green."
Now, about the absorption. This is really not as
difficult as you might think. Imagine an atom not as electrons circling a
nucleus, but rather as electrons in particular energy levels, each different
level having a slightly different configuration or some other feature. All atoms
will stay in the "ground state," the lowest energy state, unless
something causes them to be excited to a higher energy state. Light is one of
the things that can cause them to jump to a higher energy state. When that
happens, the light photons are absorbed, with all their energy going into
raising the energy of the electrons. You say, but when the electrons drop back
to the ground state, won't they just give off the same light again? Not
necessarily. Think of it this way: suppose the light that came in caused the
electron to jump from state "0" all the way to state "5" in
one jump. When the electron dropped back down, it might do it in steps: 5 to 3,
3 to 2, then 2 to 1, as an example. Result: different light emitted than
absorbed. By the way, the dropping down sequence often gives off infrared (not
visible) rather than visible light, so you don't see it with your eyes.
Lastly, why green? Very interesting question. Plants
have been made to absorb all across the visible spectrum so that they can use
all the light, not just the green center of the spectrum. Thus, they absorb red
and blue pretty well, and OK but less well in the green. Result: you see more
reflected green that other colors. This way, the plants can grow even in subdued
light that doesn't have much green! It's a benefit to us who try to grow plants
indoors with artificial, house lights that are strong in the reds and weaker in
the greens and blues. In the Fall, the same "green" plant turns red,
not because it has added the red, but because the green chlorophyll has gone
away. It was "red" all the time! The particular colors are determined
by the atoms that make up the molecules of the material as well as the way the
atoms are arranged on the particular molecules and the way the molecules bond to
one another. It's all rather wonderful for me and an exciting way to think of
the way nature is maximized to work together.
Bill Newsome, from Charlotte N.C., asks:
I work with a lot of steamers and boilers in the food equipment repair business and I have tried to find out the answer to this question for a long time. For every pound of pressure in a boiler..How many degrees of temperature rise is there for every PSI of pressure?
Steve Tonsfeldt, a physicist, replies:
For lower pressures, such as up to 20, 30 psi on the gauge, the Handbook of Chemistry and Physics has essentially 2.5 Fahrenheit degrees rise for the boiling point of water for every 1 psi increase in pressure.
Ryan, a high school student, asks:
I'm confused. Sound is a form of energy , I think, but it must travel through matter to diffuse. It exists as a wave like light does, but sound energy cannot "diffuse" unless accompanied by matter. Aren't there small particles in sound waves like photons in light waves? Also if I clap my hands in a vacuum, will the sound energy go through the vacuum and into any matter nearby? Or does the sound have to be made inside the matter?
Joe Traylor, a physicist, replies:
You are on track but have one error in your thinking. Yes, sound and light both
possess energy, but there is one very significant difference: sound is expressed
in the motion of particles. It REQUIRES particles. That is, the motion of the
particles IS sound. Yes, it is quantized, and the quantum is called the phonon
by analogy with the quantum of light, the photon. (Phonon is pronounced "foh-non"
and rhymes with photon.) So, sound is a disturbance of the positions of
particles. Sound propagates by molecules colliding with each other or by one
molecule pulling on its neighbor in solid materials. Light on the other hand is
a disturbance of the electric field, not the positions of atoms or molecules.
Thus, light can propagate in a vacuum where there is no matter. Electric fields
don't require the presence of matter. Sound can only exist in matter (any kind,
solid, liquid, or gas) and therefore cannot propagate in a vacuum. One more way
to say it: sound is mechanical, and light is electrical.
Lastly,
you asked about clapping in a vacuum. Good trick if you could do it, but don't
try. Our bodies don't behave well in vacuum! But suppose you could. Yes, energy
would still go away from your hands, but in the form of heat, not sound.
Furthermore, the heat would be expressed in infrared light waves! No sound, but
rather light! The same thing happens when you clap you hands in air, but because
to sound is so loud, you hear it and never think about the infrared that went
away as well.
I'm
impressed that you are thinking about these things! Keep it up. The atomist view
of matter and the energy view of waves are very important. Congrats on wrestling
with such significant ideas.
Matthew Russo, a college student, asks:
What is the ionization of rain water as well as it's polarity? Also (this is what this is all about)...If rain water does not have a neutral ionization can a material or field with the reciprocal ionization repel or even disperse the rain water?
Jon Hutchins, a chemist, replies:
Water is a polar molecule, but has no net charge. It contains ions such as hydronium ion and hydroxide ion, also ions formed from dissolved atmospheric gases, such as carbon dioxide and sulfur dioxide. However, the charges on all the ions will cancel out. Water droplets could be given an electrostatic charge (using electrodes) and made to move towards an oppositely charged electrode. This is the principle behind the electrostatic precipitator, used to remove tiny dust particles from power plant smoke.
Stewart Henderson, a college student, asks:
I have been given a project involving analysis of low alloy steel. I have run AAS on these samples. I am however struggling to find a decent gravimeteric method to use to compliment this. Could you suggest some methods of determining the composition gravimetrically?
Jon Hutchins, a chemist, replies:
You don't say what metal you wish to analyze gravimetrically. Nickel can be done as the red dimethylglyoxime complex. I'm sure other methods exist for different metals. I would suggest consulting a standard analytical reference text, such as Kohltoff's book, which should be available in any college library.
J. Nicol, a parent, asks:
Would you please comment on the following.
1) Cup of water brought to boiling point in a microwave oven
2) Water reheated a few minutes later in the microwave oven
3) Water did not appear to boil during 2) above although the microwave on time during this period exceeded 100 seconds.
4) Assumed microwave damaged by condensation during 1) above
5) Carefully retracted the cup at arms lenght
6) Upon reaching the cooler air outside the mwave cavity, the cup of water in its entirity flashed into steam.
Question:- What is the approximate maximum temperature that water can achieve when heated in the above manner at normal atmospheric sea level pressure ?
Steve Tonsfeldt, a physicist, replies:
You had a very close call with your microwave experiment! So-called
"superheated" fluids are dangerously explosive and are sometimes
avoided by the chemists' use of boiling beads, little glass beads they put in
their beakers.
Are you familiar with the
fact that liquids are rather strange in that they can be both superheated above
their boiling temperatures and supercooled below their freezing temperatures and
still remain liquid? For example, according to the physics, clouds shouldn't
form under the temperature conditions that are known to exist in the air. But
they do form and so there must be a mechanism. It turns out that dust, soot, sea
salt particles or other foreign matter provides nucleation sites or condensation
surfaces for the water to attach to. Those instant heat packets that are sold
are a supercooled solution that quickly freezes, liberating heat, when you
disturb it by clicking a corner tab, making a nucleation site.
In the superheating of liquids
the vapor pressure inside the very small initial cavity that forms is
artificially low because it is surrounded on all sides by liquid and so any
cavity that does form tends to collapse. This allows an unstirred liquid to be
superheated above the "normal" boiling point. For smooth boiling to
occur we again need nucleation sites such as small pieces of sharp-sided glass
or bubbles of air. Perhaps like me you have seen a small stream of bubbles
rising from scratch marks in the bottom of a pan of water on the stove that you
are going to heat to a boil.
I would suspect that your cup has
a very smooth surface and that your initial heating of the water to a boil drove
out all the initial air bubbles in the water so that there were essentially no
nucleation sites. As with the heating pouches, any bumping can cause spontaneous
nucleation of bubbles big enough to survive and the vaporization proceeds
explosively. I have heard that water under carefully controlled conditions can
be heated to 200 degrees Celsius, 100 degrees above the normal boiling
point.
I am glad that you were not harmed and that you were
curious enough to ask about why it happened. I hope this has helped
and please get back to me if I can be of further help.
Ben Myers, a college student, asks:
As I understand it, we have three kinds of cones in our eyes that respond with small electrical discharges when they're hit with specific wavelengths of light--red, green and blue. Can we consciously (or unconsciously for that matter) tell the difference between an actual purple (pure, made up of only one wavelength of light) and a mixed purple (with two wavelengths that interact as in some Impressionist art where we get little dots of primary colors)? It would be interesting to see a close up of the waveforms (simulated, since it's not actually a wave or a particle) and compare them. I wonder if the two waveforms add exactly to equal that of the single waveform of purple? Perhaps it is that we don't actually have three kinds of cones --- just a smooth frequency response over the range of visible light? Makes you wonder about other things, too. Could we mix the right frequencies of infrared light to get something visible? Thanks for your help.
Bob Ferguson, a psychologist, replies:
Ben--this
is a really interesting question; I've had fun thinking about it. You've got
several questions embedded in what you wrote, so I'll try to get to them all.
First,
it really does seem to be the case that we have 3 types of cone receptors in the
normal human retina. Each type is sensitive to a range of wavelengths, but shows
maximum sensitivity at either 420nm, 534nm or 564nm. These are often called the
"blue", "green" and "red" cones, respectively, but
it would be better to think of them as being most sensitive to short, medium and
long wavelengths. There are lots of good, solid data to confirm these 3 types of
cones, but I won't bore you with that here. What's more interesting is how they
work to produce the experience of color.
You are absolutely right that it's possible to create 2
identical appearing color patches, one from monochromatic light and one from a
combination of two or three wavelengths. For example, a patch of nearly
monochromatic yellow can be shown side by side with a patch that has no yellow
at all, instead it's a combination of red and green light (yes, red &
green), and if you get the balance of red & green just right, the 2
resulting patches will appear the same to the human observer. (BTW, such pairs
are called metamers.) Why? Because the wavelength of the monochromatic yellow
light is close enough to the "red" and "green" cones that it
simulates both of them to fire. In fact, that's how the visual system normally
codes for yellow: red + green cones firing. So, if instead we simultaneously
stimulate the red cones with red light & the green cones w/ green light, we
get the impression of yellow. As far as the visual system is concerned, IT'S THE
SAME THING!!! [Somebody should make a TV commercial using that line. ;-) ]
That's also how TV screens work. They produce tiny dots
of red, green and blue light which are so small that they seem to blend together
to a viewer seated at a normal distance. Note that the wavelengths don't really
combine--they remain separate & distinct. By varying the brightness of the
red, green & blue dots on an area, the screen produces all of the colors
that the camera sees.
Here's the simplest way to think about all
this--wavelength is a physical dimension of light that can be measured by
technology. Color is a purely subjective experience in the head of an observer.
The two are certainly related, but not the same thing. So, if a light came on in
the forest, but no one was there to see it, there would be no color.
Anthoy de Lorenzi, a parent, asks:
Looking for cleaner faster transportation in the future, has any scientist used reverse polarity as a new concept for a car or train? The way magnets repel from each other you would think there was a way to make a floating car with no friction that would not use gas. For example, what if there were big enough magnets under a special car or train and other magnets in the road or track? Is this feasible?
Shawn Stone, a physicist, replies:
You ask a very good question. Scientists have been using the repulsion of magnets for many years now. Japan has put magnetically levitated trains to use for 25 years without any accidents. Since there is no rail friction, the trains can travel at a very high rate of speed (up to 200 mi/h). This still takes energy however to get them going and keep them going (we still have to slow the train down and deal with air resistance etc.) The energy savings of magnetically levitated trains is significant using 60% less fuel per passenger than an automobile and 70% less than an air plane. Florida, Texas, and California are constructing Mag-Lev rail lines as we speak. As for cars, we are a long way from that I believe. I hope this answers your question.
Crystal M., a high school student, asks:
I was wondering how Avagadro's number was calculated and who calculated it (because I know it wasn't Avagadro).
Jon Hutchins, a chemist, replies:
According to my old P. Chem book, Robert Brown (Brownian movement fame) calculated it in 1827. The modern derivation I have runs to 3 pages, and involves calculus. I don't have time to digest it and send a simplified proof, but I can send you a Fax of the derivation, if you send me a Fax number (hutchins@bvu.edu). Click here for more details on the History of Avagadro's Number.
Shawn Stone, a physicist, also replies:
Thank you for your question. It is a good one and I had to look it up myself. In 1865 the Austrian chemist Johann Joseph Loschmidt used Maxwell's kinetic theory of gases and Avogadro's principle (gases of equal volume contain equal numbers of molecules) to arrive at 6.X10^23 particles. Since it followed from Avogadro's principle it was called Avogadro's constant.
Buddy Smith, a college student, asks:
Dumping large amounts of raw sewage into rivers or lakes often leads to massive fish kills, although sewage itself is not toxic to fish. Similar fish kills also occur in shallow lakes that become covered in ice during the winter. What kills the fish? How might you reduce fish mortality after the accidental release of raw sewage into a small pond containing large bass?
James Hampton, a biologist, replies:
Glad to read of your interest in fishkills. As I
understand it, the two phenomena, sewage kills and winter kills are related by
oxygen content. Fish absorb oxygen through their gills from the water. The
oxygen in the water is only a small fraction of what is found in the atmosphere
and it is the contact of atmosphere and water that maintains the oxygen content
of water. In winter, the ice covers the lake eliminating the contact between air
and water, diminishing the oxygen content of the water. This is why the
Department of Natural Resources wants to put an aerator in Storm Lake (in the
town where I live), to keep the ice open and give contact between water and
atmosphere. Large sewage dumps pose a similar problem since the sewage contains
a large number of oxygen consuming bacteria. The bacteria use up the oxygen and
the fish suffocate in a manner of speaking. Similar effects occur in some lakes
in the fall as the decomposing algae serve as food for oxygen consuming
bacteria, again diminishing the oxygen available to fish. Some kind of aerator
would help with a fish kill in any of these cases (similar to what most people
do in their fish tanks--you could use a fish tank to simulate some of these
conditions) but the best thing is just to avoid the sewage spill in the first
place.
One last comment, some sewage dumps kill the fish
outright because of the content of the sewage itself. Don't forget fish are
breathing that stuff, but only when the sewage is at a very high concentration.
Liz N., a high school student, asks:
The question is: In a lab, we put about a tsp. of CaCl subscript 2 and half a tsp. of NaHCO sub. 3 and 10ml. of phenol red, which is a pH indicator. When all three were mixed in a sealed plastic bag, a foamy yellow substance formed, the bag became warm, and it filled with carbon dioxide. After the reaction finished, the foam died down and a yellow liqiudy substance was left. My question is, what was the substance that was formed? My teacher doesn't know (this is a biology class) but says it was probably NaCl, Ca(CH) sub. 2, or CaCO sub. 3. She thinks it is probably not the second one. I know that the phenol red indicates pHs between 6.8 to 8, and it changed from red to yellow in the experiment. So basically, we mixed three substances which gave off carbon dioxide, heat, and a new substance, which is what? Please answer this as soon as possible! It is very important. Thank you!!
Jon Hutchins, a chemist, replies:
I am assuming the phenol red is in water, otherwise this gets more complicated. The final yellow color tells you that the final solution is acidic. This is due to the excess calcium chloride, which can react in water to form Ca(OH)Cl + HCl. The HCl reacts with the basic sodium bicarbonate to liberate carbon dioxide and form sodium chloride. So your final mixture contains NaCl, carbon dioxide, and something like Ca(OH)Cl.
Dave Williams, a teacher, asks:
What does the insulation R-value (R-factor) stand for? How can I use this information to calculate how much heat is lost from a Hot Water Heater over a period of time? I would like to calcuate how much energy a 4500 W water heater uses in one day to keep the water at 147 F as compared to 120 F and how much less it would take to use a timer to turn on the water heater at 4:00 AM, turn it off at 8:00 AM, and back on again at 3:00 PM for supper, etc. to show my students that is less energy to get a programmable thermostat instead of leaving the heater on all day.
Steve Tonsfeldt, a physicist, replies:
Hello Dave! The R-value for insulation is the
English system unit for thermal "resistance" to heat flow. It is the
reciprocal of the heat flow (in Btu) through 1 square foot of the layer per hour
per degree Fahrenheit of temperature differential. In other words:
heat flow rate (in Btu/h) = area A (in sq. ft) x delta T
(temperature differential in Fahrenheit degrees) / R (in sq. ft deg. F/
Btu/h).
In order to do your calculation comparing energy used
to keep the water at 147 deg. F vs. 120 deg. F, you will have to estimate the
room temperature so you can calculate delta T for both cases and also estimate
the insulation area A and the R-value of the insulation.
For your calculations involving use of a timer to turn
the heater on and off, you would need to use calculus to integrate the heat flow
rate equations because temperature will depend on time. Please contact me if you
need any help in setting up the equations. Perhaps the important point to make
with your students is that the heat flow rate into the room is all waste heat
and that it is proportional to T(hot water)-T(room) and that it is obvious that
reducing T(hot water) by shutting off the heater reduces the amount of waste
heat.
Hope this has been of some help!
Scott, a middle school student, asks:
Would it be possible to use ocean water when running steam turbines to create electricity? If so, could the heating of the water be adapted to condense the salt from the water, leaving fresh water which could then be used for irrigation or something else? Why is it so difficult to take the salt out of ocean water so that the fresh water can be used for other things?
Steve Tonsfeldt, a physicist, replies:
Hello
Scott! You have some very good questions about use of the ocean as an energy
source. For any heat engine to work, you must have a high temperature input
reservoir at temp. T-hot and a low temperature exhaust reservoir at T-cold, so
you would probably have to use a deeper, colder water region and a warmer,
shallower water region as your heat reservoirs. The next problem would be to
find a working fluid appropriate for your heat engine. Ideally it would be some
substance that would vaporize at the temperature of the warm water and condense
at the temperature of the cold water. Scientists have considered possibilities
like this, but the main drawback to getting energy from the ocean temperature
differences is that the efficiency of the heat engine would be very low because
of the small temperature differences available. Talk to your science teacher for
help in making the calculation, but for the most efficient heat engine possible,
the Carnot engine, efficiency = T-hot - T-cold divided by T-hot, where the
temperatures are absolute temperatures in Kelvins.
Your question on the process of distilling fresh water out of
sea water is also a good one. Unfortunately it is very expensive in terms of
energy at 540 calories per gram of water. Various desalinization plants around
the globe have found it more efficient to use osmosis techniques for separating
out fresh water. Ask your chemistry teacher for details on how osmosis works -
it is a fascinating phenomenon! Hope
this has been of some help.
Kirsty MacArthur, a middle school student, asks:
When is there the highest level of oestrogen in the menstrual cycle?
Jerry Poff, a biologist, replies:
In order to answer the question we have to assume the menstrual cycle is 28 days long. That is not necessarily the case but it is an average length. If we make that assumption the estrogen(oestrogen) level is the highest on the 12th day after menstruation begins and a day or two before ovulation. Thanks for the question!
Jeff Smith, a high school student, asks:
Is there any way to tri-sect an angle?
Tim McDaniel, a mathematician, replies:
As
you know, to "tri-sect" an angle is to divide it into three precisely
equal parts (i.e., into three angles whose sum is equal to the original angle
itself.) Can it be done?
Mathematicians
have proven that there is no way to tri-sect an angle by construction. "By
construction" means you're allowed to use something to write with (pen or
pencil), an unmarked straight edge, and a compass. Notice I did not say,
"No one has yet figured out how to tri-sect an angle by construction";
instead, it has been proven that it cannot be done by construction!
However,
you can tri-sect an angle using a computer and appropriate program. You can also
tri-sect an angle without a computer by hand using an implement known as an
"Archimedean Spiral." Notice that in each of these cases you are
violating the constraints associated with "by construction" that I
discussed above.
Thank
you for the great question! Keep them coming!
Dali, a college student, asks:
I want to make a medium similar to the Rembrandt medium. This includes boiling linseed oil with an oxidizing metal of low melting point which used to be lead. This made the oil dry faster. Can I use another metal instead of toxic lead?
Dennis Dykema, an artist, replies:
I'm not sure I can be of much help here. Many years ago I mixed up this medium,
and I remember it as a dreary and time-consuming affair for a small amount of a
really great medium. Knowing the toxic features of lead, I'd never do it again.
A look at the periodic
table should suggest some possibilities, but with my limited knowledge of that
table, I'd suspect that there aren't any metals with the properties needed for
this medium. Aluminum melts at a much higher temperature, and gold and silver
are too expensive, (among other things). Zinc is the only possibility I can
think of, though even that may have too high a melting point. Sorry I can't be
of more help.
I'll add this though, with
the thought that you might be willing to try a substitute. NOTE: you can stop
reading here if you're a purist, and go out a buy a very good ventilation system
for when you're cooking the lead based brew.
Otherwise try Liquin, a
product by Windsor and Newton. It works well in making a paint with nice
brushable qualities, it accelerates drying time, and retains a reasonable
flexibility of the paint surface. I go further by mixing Liquin, Stand Oil, and
Damar Varnish in a !:!:! ratio.
Kim Griffith, a high school student, asks:
Can a solid freeze? How? What are some examples? How does this change happen? Do the particles change in any way?
Steve Tonsfeldt, a physicist, replies:
Hello Kim! For the purpose of chemistry and its characteristic energies, the atoms are the building blocks that are unchanged in any physical change such as freezing. Usually we use the term freezing to describe the process of going from the liquid state to the solid state, from where the atoms or molecules are free to slip and slide around, to where the atoms or molecules are "locked in" to specific geometrical arrangements, such as in a crystal. But, depending on pressure and temperature, different solid structures are possible for the same atoms. Perhaps this is what you had in mind when you asked whether a solid could freeze. For example, water ice can exist in a large number of solid phases, depending on temperature and pressure. Likewise pure carbon can exist as graphite (like your pencil "lead") in a low pressure and temperature environment such as the surface of the Earth and as diamond under conditions of higher temperature and pressure deeper inside the Earth. I hope that this helps answer the questions you have posed!
Heidi asks:
Can you tell me as much as you know about the BRADFORD METHOD? It's used for protein determination and for protein quantification. I specially want to know in which cases it's not possible to use this method.
Jon Hutchins, a chemist, replies:
Regarding the Bradford method: I think you would need a water soluble protein. Otherwise you could do a total nitrogen determination by the Kjeldahl method. You need reagents (see Bio-Rad supply company) and a color measuring device (eg: a Spec 20 spectrophotometer) operating at 595nm. A procedure is given on p.20 of Experimental Approaches in Biochemistry and Molecular Biology by Zeidan and Dashek. Publishers Wm. C. Brown (1996). Good luck!
Dana Beeman, a middle school student, asks:
What can you tell me about the different chemicals in bleach? I couldn't find much at the library.
Jon Hutchins, a chemist, replies:
Bleach is basically a water solution of sodium hypochlorite (Na+ ClO-). Hope this helps.
Jared Minnick, a high school student, asks:
I have been looking like crazy to find a definition of a "heavy metal". I have looked at numerous inorganic and other chemistry books, dictionaries, encyclopedias etc. and the closest I could come was "a metal that has a high molecular weight". This is not in depth enough for my needs. What separates a heavy metal from other metals? Are their specific differences other than weight? Thanks.
Tim Ehler, a chemist, replies:
By definition, heavy metals are considered heavy because of their higher molecular weight. The heavy metals, those primarily near the bottom of the periodic table, exert their action primarily by inactivating enzymes; enzymes catalyze reactions by binding a reactant molecule at an active site. Most enzymes have amino acids with sulfhydryl (-SH) groups. Heavy metal ions have the tendency to tie up these groups rendering the enzymes inactive. One specific example is that of mercury, formerly known as "quicksilver", poisoning. Mercury ions will react with the sulfhydryl groups of an enzyme causing a change in the enzyme's physical shape. This change in shape will destroy the enzyme's active site rendering it inactive. Fortunately, there are antidotes for mercury poisoning.
Heavy metals are also perhaps the most common of all water pollutants. The most frequently encountered heavy metal elements are those of lead (Pb) and mercury (Hg). Some less common elements include cadmium, chromium, nickel, and copper. Most often, it is inadequate disposal of wastes from mining or industrial activities that causes these metals to find their way into water supplies.
Karen, a parent, asks:
We tried an experiment with 2 jars of water each containing the same quantity of rock candy. One jar sat on the table, unstirred, and the other was heated. Of course the heated one showed a quickend dissolving of the solid. Why? Is it because the hot water molecules are bombarding the solid more frequently, rather like more surface area exposed? Is it because the heat breaks the bonds between the molecules? I'd like the question answered with regard to the molecular activity so an 8-year-old can grasp it.
Shawn Stone, a physicist, replies:
Rock candy is a large crystal of sugar. The molecules of sugar are loosely held together by a type of molecular bond called an ionic bond. When the water is heated this gets the molecules of water to start jiggling around much faster and harder than cold water. These water molecules now are moving fast and carry a lot of energy with them (this is known as heat). When they run into the rock candy, they have enough energy to knock some sugar molecules loose (more molecules than the cold water). Also, this happens at an increased rate since the molecules of water are moving around faster.
Carlos, an Italian pharmacist, asks:
Hi.
I'm writing from Italy. I am a pharmacist and today I had to prepare a water
solution of citric acid 10%. The only two compounds were water and citric
acid. We have some books to help us in this situation and looking up
citric acid I found that in diluted water solution citric acid transforms itself
into ossalic acid by fermentation. I would like to know
1- If
this is true? and, if true,
2-
Under which concentration does this happen?
3- How
fast is this process?
4- What
are the conditions that help or disturb this process?
Thanks for the help.
Jon Hutchins, a chemist, replies:
I think you are talking about conversion of citric acid to oxalic acid. Fermentation requires some living organism (microbe). If this is not present (sterile solution) citric acid should be stable. After all, it is present in many fruit juices. Oxalic acid, incidentally, is toxic, so fermentation is to be avoided. The reason fermentation of dilute solutions may be a problem is pH. Lowering pH by using stronger solutions probably slows down fermentation.
Sara, an 8th grade student, asks:
What is the meaning of 'rate' in physical science?
Steve Tonsfeldt, a physicist, replies:
Rate involves two changes. Usually changes that occur as time passes are easier to understand. One example would be speed, which is the rate at which distance changes as time changes, and is therefore defined as the change in distance divided by the change in time. However, rates or changes can occur when variables other than time change, such as the concentration of one substance in a solution changing because of the addition of another substance of varying amount. Or one could talk about the change in average height for the countries in Europe as one goes from North to South there. There are many examples that one can come up with. The main point to remember when someone talks about "rate" is that one thing is changing because something else is changing. Hope this has been of some help!
Ashlee, a parent, asks:
Is light from a fire matter?
Shawn Stone, a physicist, replies:
Thanks
for your question Ashlee, it is a very good one.
What defines something as matter is the property of mass (how
much stuff they are made of). We can tell that everyday objects have mass
because we can touch them and see them. They are quantifiable to us and so we
have no question that they have matter (mass). For light, things become a little
bit harder to measure. We do know that light can be considered to be made of
particles called photons. However, we do not have an instrument that can measure
the mass of a photon directly. This is where things get a little bit
complicated. It was Einstein who discovered an equation that helps matters a
little, E=mc^2. This is a relation that states that energy is mass multiplied by
the speed of light [c] squared. It effectively finds that matter is energy and
energy is matter. You know that from sitting next to a fire that you feel warm
much like the Earth is warmed by the sun. This light carries energy, and must
contain some mass (matter) according to E=mc^2, but we have not been able to
experimentally verify (measure) this yet.
I hope this was not too complicated. If you have any
other questions, please do not hesitate to ask.
Tami, a college student, asks:
Why do you think people view psychologists as being different from scientists?
Bob Ferguson, a psychologist, replies:
First, what evidence do you have that they do? Personal experience? Common Sense? Anecdotes? As I see it, contemporary psychology is centered around the notion that these are not reliable sources of information if we really want to understand human behavior. Instead, we need to do systematic observation under controlled conditions (can you say "experiment"?) where alternative hypotheses can be ruled out. And therein lies part of the problem, as well as part of the answer to your question. Many of the most interesting & important questions about the human condition are not especially amenable to controlled experimentation (for example: What went wrong at Columbine?). This leaves the door wide open for all kinds of speculation, much of which can never be tested, but is very popular on talk shows and in popular bookstores. Combine this with the fact that anyone who is willing to write or talk about human behavior is often regarded as a 'psychologist', & I think the outlines of an answer to your question begin to emerge.
Finally, one last factor probably also plays a role--a phenomenon from social psychology called the 'availability heuristic', which simply says that we often base our judgements about people or events on those instances which are most 'available' to us--i.e., the ones that are most memorable. And who are the most memorable 'psychologists'? Freud, Jung, Joyce Brothers, Dr. Ruth, and Bob Newhart (at least for those of us old enough to remember his TV show). Most of these are not even psychologists, and none are typical of the profession, yet they define psychology for much of the population.
So, IF it's true that psychologists are viewed differently from other scientists (and that's a testable question), these may be some of the explanations.
Corinna asks:
Do you think that stabilized oxygen can be used in place of iodine or chlorine to purify water? Is it safe used in conjunction with a .01 micron water filter?
Jon Hutchins, a chemist, replies:
Ozone (O3) is widely used to disinfect water, especially in Russia, I believe. It is made by an ozone generator which requires electricity and air, but no other chemicals. I would not describe ozone as stabilized oxygen, actually it is destabilized. Some oxygen releasing agents (oxidizing agents) may well be useable for disinfecting, but I don't know the specifics. Obviously the byproducts would need to be non toxic.
Louise McCarney, a college student, asks:
Why does blowing on a lighted candle, if blowing hard enough, put it out? What is the flame and what are the conditions necessary to sustain the flame? How does blowing on the flame alter these conditions so that the flame is no longer sustained?
Steve Tonsfeldt, a physicist, replies:The question about why blowing hard toward a candle will put it out is a very good one! Most people are already thinking about eating the birthday cake under the candles. Candles have a lot of chemistry and physics in their operation. Michael Faraday gave a whole series of lectures entitled "The Chemical History of a Candle" in 1848 in the famous Christmas lectures at the Royal Institution in England. If you are interested in the topic, it is covered in a book in the Scientific American Library series called "Fire" by John Lyons, W.H. Freeman Pub. As for the question, recall that a candle is solid and needs to melt (which takes energy) and that capillarity takes the liquid up the wick to the point where the liquid is vaporized (which again takes energy) and this vapor is burned in the flame. You can prove this by blowing out the candle and quickly hold a lighted match not to the wick, but above the wick. The candle will relight! So the heat from the flame is necessary to do these conversions and also to provide the activation energy for the combustion reaction itself. If you blow gently , it will burn brighter because you are feeding in more oxygen, like a bellows at a furnace, but if you blow too hard I think you blow the heated air away from the wick and the temperature drops below the combustion temperature. Hope this helps! It's a very good question about a fascinating phenomenon.
Laura Mangan, a high school student, asks:
My I am doing a paper on beer for chemistry and I need the chemical compound for it, and I can not find it. I also am showing the difference between beer and non-alcholic beer and having no luck. Jon Hutchins, a chemist, replies: Beer contains a huge variety of compounds, derived from grain, from yeast, and from hops. I suggest looking at a science encyclopedia if you need further details. The major constituent is water, with about 4-5% ethyl alcohol. This last material is mostly removed in non-alcoholic beer. Marisa Szeps, a grade school student, asks: My science project has to do with attracting and repeling forces due to electrical charges. I inflated two balloons and attached them to string. I hung both from a door jam. I rubbed each of them ten times against my hair. They should have attracted but I could only get them to repel. Why? Why? What influences the electrical charges and can you suggest a way to make it work? Steve Tonsfeldt, a physicist, replies: Marisa, your balloons acted properly by repelling each other because since you prepared them the same way, they had to be of the same charge, and like charges repel. I think they were both negatively charged. To see why, let's start with this. Materials are made of atoms and atoms are usually neutral - they have as many electrons as protons. However the outer electrons are held less tightly and are most easily shed. The process is not entirely understood, but different materials (different atoms) have different attractions for these outer electrons. For example, if you lay a piece of Saran wrap on a metal bowl, it will cling, because electrons are transferred from the plastic wrap to the more-grabbing metal. Rubbing really only effects things in increasing the area in contact and not much else. Anyway, by comparing different materials placed in contact, a so-called triboelectric sequence can be generated. The following list is taken from Physics, by Eugene Hecht, 1994, Brooks/Cole Publishing: asbestos, rabbit fur, glass, mica, wool, quartz, cat fur, lead, silk, human skin or aluminum, cotton, wood, amber, copper or brass, rubber, sulfur, celluloid, India rubber Of any two materials from the list placed in contact, the first becomes positively charged and one listed anywhere after it becomes negatively charged. Since human skin and the furs(human hair also?) are before rubber it looks like they become positively charged and your rubber balloons become negatively charged. In order to get attraction you need to rub one balloon with sulfur or celluloid to make it positive, so that it will then attract your negative balloon. Give it a try and good luck!Fran Knobel, a parent, asks:
My son recived an "E" on his science fair project. His teacher said, "Your project was more of a survey than a scientific project. You did not have an independent/dependent variable." Please explain these variables. His project was "Which Greens Do Kids Prefer"--Spinach, Broccoli or Green beans." 25 girls and 25 boys, both between the ages of 6 and 12, were asked. Bob Ferguson, a psychologist, replies:I'm thinking about tracking systems for the theatre, that is using an array of antennae to measure the level of a radio signal coming from an RF transmitter, then compairing and triangulating to get the location. I think i'd need three antenna for a 2D space and 4 for a 3D space.
Joe Traylor, a physicist, replies:
Yes, there are atmospheric effects, but they are not likely to be a problem for you in theater. Relections from walls, steel superstructure, etc, may be more of a problem, but even then may be accounted for during your calibration exercise. The difficulty is that, due to reflections and the resulting interference caused by them, that the signal strength from a transmitter can vary *greatly* as the person moves from spot to spot on stage. This is why typical auditorium wireless PA systems usually use two antennas instead of one; when one receives a weak signal, the second may receive a stronger one. The weakened signal can occur just because the speaker turns his/her head.
Triangulation is the basis of GPS, the global positioning systems, so you're on the right track.
As I recall, you are at ISU. No doubt the ISU library has a bunch on this. I suggest you check it out. Check out the ARRL Handbook and look under vhf and uhf, and on the web, www.arrl.org. Search the technical area.
Don Hall asks:
Does sodium have a frequency? Can it be manipulated by ultrasound? 33mHz? Can sodium be mutated into another form? chlorites? This is a project to rid brine content of drilling water.
Jon Hutchins, a chemist, replies:
Sodium ion can be removed from water by ion exchange, reverse osmosis, distillation, possibly by complexation. Changing another sodium salt (eg a chloride) to a chlorite really does nothing to the sodium, only the anion. I'm unsure about the ultrasound question.
Sara McKean, a high school student, asks:
In what stage of pregnancy is the gender of the baby determined?
James Hampton, a biologist, replies:
The gender of a human baby is determined at the moment of conception. Human sex determination is based on the complement of sex chromosomes. Females have two copies of the X chromosome in addition to 44 non-sex determining chromosomes (autosomes). Males on the other hand have only one X chromosome and have a Y chromosome that includes genes to make them male. When eggs and sperm are produced, collectively called gametes, they receive only one of the sex chromosomes. Since women have only X chromosomes that is all that eggs can have. However, males have both X and Y so half of sperm contain the X chromosome and half contain the Y. If the egg is fertilized by a sperm containing the X chromosome, then the baby will be a girl and this is determined from the moment of fertilization. On the other hand if a sperm carrying a Y chromosome gets to the egg first, then the zygote and resulting baby is male.
This method of sex determination is not universal. There are almost as many methods of determining sex as there are possibilities. Some species, like many birds, have females that are heterogemetic W & Z chromosomes while the males are homogametic ZZ. Some creatures like crocodiles have sex determination based on the temperature of the egg while it is incubated, one sex coming from cool eggs and the other from warmer eggs. There are many shellfish that start out life as one sex and change to the other as they mature. Finally, there are some fish that can be either male or female depending on the environment in which they find themselves.
Shannon Hill, a middle school student, asks:
I am doing a science project to see if adding horse manure to a compost pile will speed up the process of the decomposition of the material within the pile. My project is all set up and going, but I am unsure how to go about measuring decomposition in a scientific way. There are two piles, each with soil, egg shells, potatoe and apple peelings, and a coffee filter. One of the piles has the added horse manure. Please help. Thanks.
Chad Scholes, a biologist, replies:
There isn't a simple way to measure decomposition. I will mention several things that may be useful to you for your experiment. Decomposition is dependent upon living things feeding on the material. Compost piles typically have many types of organisms that are associated with them. Macroscopic organisms such as earthworms, millipedes, mites, and other invertebrates are important initially in breaking down the large pieces of material into smaller ones. When the pieces are smaller then fungi, protozoans, and bacteria will do most of the work. Therefore, observations of the organisms associated with the decomposing material can indicate the rate of decomposition. As organic material decomposes, the structure, texture, and color of it often changes. Frequent observations and pictures will help you document the rate of decomposition. One easy way to measure this might be to measure the height of the pile of material, assuming that you do not disturb it. Decomposition usually results in the production of many gases. Two of the gases that will be produced are carbon dioxide and methane. If you have your compost piles in a type of container you could cap them and measure gas production (possibly with a balloon) as an indicator of rate of decomposition. One of the problems with capping your compost piles is that the organisms doing the decomposing need lots of oxygen to do a good job. Some organisms can decompose without oxygen, but it is usually slower and much smellier. Compost piles are usually fertilized and inoculated with organisms to help begin decomposition. Which of these do you think your horse manure will do?
Jean Bogart, a middle school student, asks:
The question is: I am an 8th grader who is fascinated by artificial intelligence. For my science project this year, I'm considering coding a very crude, simple chatterbot. Anyway, do you know what language would be best to program in (preferably an easy version of BASIC if possible?), how I could get started, and where I could find some source code to use as a template? (Or will I have to start from scratch?)
And if this is too difficult to be attempted, I apologize for wasting your time. I actually designed a similar program last year--without any adult help--and the results were less than encouraging. However, I did manage to create a very simple conversational program using an old Apple IIe and a whole lot of code in BASIC.
My research led me to this page (I believe you teach courses in artificial intelligence, or something of that kind). I hope you can answer my question, since this has been my dream project for quite some time.
Thanks! :)
Ken Schweller, a computer scientist, replies:
Thanks for writing Jean. You came to the right place. My hobby is constructing conversational bots and I have created them in many languages, including BASIC. One of my bots who goes by the name of 'MrChat' is especially notorious. He has appeared in two books already.
 |
Outline
of "High Wired: On the Design,
Use, and Theory of Educational MOOs" University of Michigan Press, 1997. Contains a chapter by Ken. |
 |
Andrew Leonard's book Bots devotes a chapter or so to Collegetown's MrChat programmed by Ken Schweller |
MrChat will be appearing by himself in a full chapter interview in a new book out Fall 1999. You can learn to program a bot like MrChat by visiting the CollegeTown Virtual Community at Buena Vista University and applying for membership. Once you log onto CollegeTown you can proceed to Ken's Office to talk to MrChat or to the TV Studio where you can ask to have your own bot which you can then program. This bot is created using a special object oriented programming language called MOO code. If you log onto CollegeTown contact Ken (me) for further details. Press here for further instructions on programming a conversational bot and here for details about the Loebner Contest, an annual contest pitting bot against bot to see which appears most intelligent. Caution: None of these bots has come anywhere close to passing Turing's Test which challenges a user to pick which of two conversationalists is a bot and which a human simply on the basis of keyboard output. All conversational bots use simple pattern matching, key words, and random responses to create the illusion of intelligence but they understand little or nothing about what they are saying.
Ajit Dubhashi, an electrical engineer, asks:
I am an electrical engineer so perhaps my question is really stupid. I need to have a surface completely free of silicone. We suspect that the surface has a thin film of this on it which causes poblems. Is there a simple quick test that can be performed on the surface such as 'add a drop of alcohol, add a drop of XYZ and look for change in colour etc' ? We have tried using UV light that causes the material to flouresce but this is difficult for thin films. Thanks for your help.
Jon Hutchins, a chemist, replies:
Probably the standard way would be infrared analysis, using some surface technique involving bouncing IR across the surface, and seeing what wavelengths are absorbed. I don't know of any simple chemical test (silicones are pretty unreactive), however, a physical test involving wettability might work. Sorry, don't know the details. Finding a very good clean solvent to remove the oily silicone layer is, of course, important. Good luck!
Joanne H. Davis, a teacher, asks: The question
is: We are currently building series circuits. The light source we are using is a LED. The
energy source is two "d" cell batteries connected in series. When we hook in one
LED it works fine. However, when another LED is added, the batteries will not carry the
load. Why does it take so much voltage to run a LED?
Joe Traylor, a physicist, replies: You've asked a
good question that has a subtle answer. It is not that the battery can't "carry the
load" but rather the LED itself causes a voltage drop that is more than half of the
battery's voltage. Therefore, two of them in series require more voltage than a 1.5 Volt
cell can deliver. Voltage is a funny concept. A good way to think of it is the ability to
cause current to flow. Thus, a 3 V battery can push current twice as strongly as a 1.5 V
cell. Now, LED's are like a tall hill. It takes a minimum push (voltage) to get up the
hill, called a threshold voltage. The particular value depends on the materials used to
make of the LED, but typically they are between 0.6 and 0.9 V. Less than that threshold,
and no current flows. More than that, and yes, it flows and lights the LED. Put two of
them in series and EACH requires that much of a threshold voltage. A typical 1.5 V cell
will likely not have enough push to do them both, but one D-cell should be able to light
one LED. But you say, you've already tried two batteries. Now you may have a second
phenomenon going on. Were the batteries new? (I mean, brand new from the store.) As carbon
batteries get old --both in age and in use-- the internal resistance of the battery
increases dramatically. Alkalines not as bad, and lithiums less yet, but all do it to a
degree. If you measure the voltage of the battery with a voltmeter, it will probably read
1.5 V. But, in a working circuit with current flowing, the resistance of the battery
itself eats up much of the energy, and the effective voltage available to the rest of the
circuit may be much lower than 1.5 V. (This is the reason car batteries don't work well in
cold weather; the internal resistance increase as temperature decreases.) Suggestion: to
confirm what I've said, try two NEW batteries in series with two LEDs. The voltages of the
two batteries will add and make a total of about 3 V and should light both LEDs. Good
luck! Second suggestion: Try one battery and two LEDs, but this time wire the LEDs in
parallel. If both light, your battery has enough ummph to carry the load.
Kara Ellis, a teacher, asks: Can you explain, in third grade
terms, the process of the Earth revolving and rotating around the Sun? My students are
having some difficulty with the concept that the Earth revolves, the Moon orbits around
the Earth, and the Earth and moon together orbit the Sun. Can you help us out?
Mark Biermann, a physicist, replies: The motions of the moons about
planets and of the planets about the sun is one of the most fundamental questions in all
of science. It is not surprising that your students are having some trouble with the whole
concept because aspects of this question have been challenging scientists for thousands of
years, and many questions still remain. When you ask about the "process" of the
Earth revolving and rotating there are two basic aspects of the question that must be
dealt with: what is happening and why it is happening. Let's look at the "what"
part first. Our solar system consists of all the objects that orbit, or revolve, about the
sun. The sun is a star and is incredibly large compared to the other objects in our solar
system. The primary objects in the solar system, besides the sun, are the planets and the
moons that orbit the planets. Not all of the planets have moons, and some planets have
many moons. It turns out that the earth has one moon. Venus, which is about the same size
as the earth, has no moons, and Mars, which is much smaller than the earth, has two moons.
This is just the way things are in our solar system. One can picture all of the planets
lying in one plane that passes through the sun. That is, if you were to set the sun on a
table (you would need a big table), all of the planets would pretty much lie on the same
table top. Being one of the planets, the earth travels in an orbit about the sun on the
same table top as all of the other planets. The path that the earth follows as it
revolves, its orbit, has the shape of a slightly flattened circle, called an ellipse. The
earth's orbit is very close to a circle, but is not quite a circle. The earth moves along
this oval path all of the time and repeats one full circle each year. So, it takes 365 and
a quarter days for the earth to get back to the same place in its orbit. In the same way
that the earth orbits about the sun, our moon orbits about the earth. The orbit of the
moon is an ellipse, an oval that is not quite a circle. If we go back to thinking about
the table top, the path of the moon does not quite lie on the same table top as the path
of the earth. For half of the moon's orbit it is above the table top, and half of the time
it is below the table top. Note, however, that this tilt is actually quite small. Since
the moon orbits about the earth, it follows the earth along in the earth's orbit. The moon
always stays centered on the earth and since the earth is moving, the moon must follow
along with it. The moon only takes about 29 days to complete one full orbit about the
earth. Thus, while the length of a year is based on the time for the earth to orbit the
sun, the length of a month is about the length of time it takes to moon to orbit the
earth. The motion of the earth about the sun, and of the moon about the earth goes on
constantly. At certain times, the moon can get between the sun and the earth. The moon is
about 400 times closer to the earth than the sun and so it is never in danger of getting
lost to the sun. However, when things line up just right, the moon can block our view of
the sun from earth. We call this a solar eclipse, since the moon is blocking, or
eclipsing, the sun. If the earth gets between the sun and the moon, which happens fairly
often, we get a lunar eclipse, since the earth blocks the sun from the moon. While all of
this is going on, the earth continues to spin on its own axis like a top. However, the top
is slightly tilted. Go back to the table top idea. The earth is revolving, or orbiting, on
the table top. However, it is not spinning straight up from the table top. Like many
spinning tops, the earth leans a little bit to one side as it spins. The spinning of the
earth is what gives us day and night. When the side of the earth someone is on is facing
the sun, that person has day. When the person is facing away from the sun, that person has
night. If the earth were pointing straight up from the table top as it spins all the
people on the earth would have the same length of day and night. That is all people would
have 12 hours of day and 12 hours of night in every 24 hour day, because 24 hours is how
long it takes the earth to complete one spin. Because of the tilt in the earth's spin,
only the people on the equator have 12 hours of day and 12 hours of night all of the time.
All the other people on the earth have longer days during the summer and shorter days
during the winter. Well, this has gotten quite long. But before I quit I should say a
little about why the sun and the earth and the moon move the way that they do. The whole
solar system is held together by a force called gravity. Gravity is one of only 4 basic
forces that we know about. Gravity exists between any two objects that are made of matter.
It is always a force that wants to pull the objects together. So, it is gravity that holds
you to the surface of the earth and it is gravity that holds the moon to the earth and the
earth to the sun. Many other details can be discussed, such as why things formed as they
did in the solar system and why the orbits have the shapes that they do. These are rather
complicated so I won't go into them now. However, if you want me to do so, let me know and
I will be happy to try. I hope this at least starts to answer your question. It is a great
question and I hope you keep on thinking about it.
Kim Ringeisen, a parent, asks: Which is heavier, cold water or
hot water ? If hot water is heavier, why does cold water lay lower than the hot water
layer in the oceans? I believe that hot water is heavier due to its expansion - it has
more mass, but sinks because it is more dense - is this true?
Mark Biermann, a physicist, replies: You have posed a very good
question. Water is a unique substance in the way it changes with changes in temperature.
Most liquids follow a simple pattern: as the temperature of the liquid increases, the
liquid expands. The other way of saying this is that as the liquid cools, it contracts. As
the liquid contracts, it becomes more dense. That is to say, more mass gets packed into a
smaller volume of space. So, a cube of a liquid with dimensions of one inch on a side will
contain more mass if it is more dense than another liquid. The more dense liquid will thus
have more mass per volume, and, hence, more weight per volume. This will cause it to sink
below a liquid that is less dense. For most liquids, then, the rule is simple. The colder
the liquid, the more dense it is. Thus, the coldest part of the liquid is always at the
bottom. But then there's water. Over a wide range of temperatures, water acts like most
other liquids. From 100 degrees Celsius (212 degrees F) to 4 degrees C (39.2 degrees F),
water will contract as the temperature drops and expand as the temperature rises. However,
from 4 degrees C to 0 degrees C (32 degrees F) water does just the opposite. As the
temperature of water drops from 4 degrees C to 0 degrees C, water actually expands. So,
water is most dense at 4 degrees C and water at this temperature will always sink below
water at any other temperature. The interesting behavior of water from 0 degrees C to 4
degrees C is why water always freezes at the surface. Water freezes at 0 degrees C (32
degrees F). Say we have a lake and that fall is going into winter. The air temperature is
cold enough that the water in the lake starts to cool. Water near the surface drops from
about 55 degrees F (13 degrees C) to about 46 degrees F. The cooler, denser water sinks
below the warmer water below it. But now the surface water cools even more. It drops below
that all important temperature of 39.2 degrees F. Now, as the water cools further, it
becomes less dense. Instead of sinking, it floats at the surface of the lake. When the
temperature of the surface water reaches 32 degrees F, it freezes and we get ice on the
surface of the lake. The sort of "backwards" behavior of the water just above
the freezing point makes this possible. I hope this answers your questions. Water is
certainly a wonderful substance. It's what makes the earth unique among the known bodies
in the universe.
Cory Loes, a college student, asks: If black is the lack of all
colors, and when a person uses bleach, bleach is suppossed to abstract all colours, then
why does an object turn white, instead of black? White is all the colors on the spectrum.
Maybe I am wrong, but just wondering.
Mark Biermann, a physicist, replies: You have gotten into a subject
that has caused much confusion over the years and for good reason. It can be a confusing
topic. The key to minimizing the confusion is to keep in mind a clear distinction between
two closely related, but very different, parts of this problem: color and pigment. Color
is best defined based on light itself which provides us with the information that the
brain needs in order to perceive color. White is in fact the color that you get when all
of the colors of the visible spectrum of light are combined together. So, white light is
the light produced by the sun and other sources that produce a continuous spectrum of
light that includes all of the visible colors. Now for the other part of this problem:
pigment. Pigment is a dye or something similar. It is added to cloth or paper or paint or
whatever to produce different colors. How does it produce different colors? Let's take the
example of a piece of red cloth. When white light falls on a piece of red cloth the
molecules of pigment in the cloth act in such a way as to absorb all of the colors of
light EXCEPT red. The red light is reflected off of the cloth and travels to the eye of an
oberver. For this reason, the observer sees the cloth as being red, because only red light
reaches the observer's eye from the cloth. And this is pretty much the way things go for
all different colors. The pigments in the materials selectively absorb some colors and
reflect other colors. The color we see for a given material depends on what combination of
colors of light have been absorbed or reflected. Now think about paints. I remember mixing
different colors of paint together to see what color I'd end up with. By mixing different
colors of paint, I was producing different combinations of pigments that absorbed and
reflected different colors of light. Different combinations of pigments produced different
colors of paint. However, one combination always produced the same result. When I combined
all of the paints together I always got black (or maybe a really dark brown). This makes
sense when we think in terms of what pigments do. Pigments selectively absorb certain
colors of light. If we combine more and more pigments together, more and more colors of
light get absorbed as a general trend. When all of the pigments get combined we are
getting the maximum absorption possible. All of the different colors of light are getting
absorbed and so, of course, the resulting paint looks black. In summary, a combination of
ALL the pigments leads to ALL of the colors of light being aborbed so that NONE of the
colors get reflected to your eye and you get black paint. Note that things actually get
rather complicated when dealing with pigments, but the general idea of the above argument
holds true. Now how does bleach fit into all of this? We use bleach to make clothing look
nice and white. To get something to look white, we want it to reflect as much of the white
light that shines on it as possible. Hence, we want as little absorption as possible. What
bleach does, then, is to remove as much PIGMENT from the material as possible. The absence
of pigment allows for all of the colors of light to be reflected from the material and so
it looks white. So bleach does not remove "color" from cloth. It removes pigment
from cloth. While combining all of the colors of visible light together does give you
white light, combining many different pigments together does just the opposite. If we want
something to look white we need to remove those pigments. That is what bleach is for.
Ben Meyers, a high school student, asks: I have a question about
your book. (Physics of stereo/quad sound) In section 6.5 you talk about column speaker
systems in which multiple loudspeakers reinforce each other to produce a more directed
wave. This happens because at certain angles away from directly in fromt of the column the
waves cancel with each other and in front of the column the two waves line up crest to
crest and trough to trough. That's the part I don't understand. Why do you get 4 times the
intensity directly in front of the column instead of just summing the intensities of the
two lou dspeakers? And is the energy that is directed away from the normal and then
canceled out ju st wasted? If it is... that's a bummer. Someone told me something about it
being in my trig/algebra class this year (some double angle identity thing) but i don't
remember. thanks.
Joe Traylor, a physicist, replies: Thanks for reading my book! It's
flattering to any author to have people read their work and ask questions. Your question
relates to how two (or more) waves interfere. You are right: the AMPLITUDES of the waves
just add or subtract. Thus, the resulting amplitude of the total wave is just the sum of
the amplitudes of the individual parts. However, the intensity of the wave is what our
ears respond to, and that depends on the SQUARE of the amplitude. That means that if two
waves of equal amplitude are perfectly in phase, the total amplitude is twice as great but
the intensity is FOUR times as great, since 2 squared is 4. When two speakers both give
off sound, there will be some places where the intensity is four times as great as one
speaker would make. (Or, if there are 10 speakers, there will be some spots where the
intensity is 100 times as great as from one!) In other places the waves will cancel each
other giving zero amplitude and zero intensity. (If you're interested, check out pages
12-14, 121-123 in the book.) The result is that you can combine several speakers in a
single cabinet to produce a pattern of sound that is very intense in some directions and
almost negligble in others. This effect is used to focus sound on an audience, rather than
sending it up or back where there are no people. You asked about the energy. Don't worry;
no energy is lost. If you calcualted the total energy produced, you would find it to be
the same as the total of each single speaker. The intense regions have high energy and the
quieter ones low energy, but the total over all directions is the same. So, you could
think of the focussing effect as focussing energy as well as focussing sound. Fascinating
topic! Glad you asked!
Leia, a grade school student asks: Why is the middle of the earth
so very hot that it melts rocks?
Joe Traylor, a physicist, replies: A very good question! The center
of the earth is so hot because of the enormous pressure that the outer parts of the earth
exert on it. You are familiar with the effects of gravity holding you down to the earth,
making things fall toward the earth when dropped, etc. Most people don't think about the
fact that the earth itself is held together by gravity! That means that the matter on the
outer parts of the earth is really pushing down on the insides, and that push causes high
heat. The same is true for every planet. A real life example of this: when a car drives on
ice, sometimes the weight of the car causes enough pressure to cause the ice to melt-- at
least enough to make a slick layer of water on top fo the rest of the ice. Makes driving
in icy conditions even worse. By the way, bet you didn't know: the very center of the
earth is actually solid, not liquid! Yes, most of the core is liquid, but at the very
middle it's thought to be solid again. The reason is the same: the enormous pressure. In
the very center, the pressure is so high that even at the high temperatures, the materials
are pressed together to be solid!
Garrett McLeish, a college student, asks: If a beam of light
shines on a sphere whose diameter is equal to the diameter of the light beam, is the total
surface of the sphere equally shadowed as it is lit? Is there an exact border where a
shadow (dark) and light meet? Are any reactions taking place at this border as well?
Mark Biermann, a physicist, replies: If a sphere is centered within
a beam of light that has the same diameter as the sphere, then one half of the sphere
would be illuminated and one half of the sphere would be in the dark. The side facing the
beam of light would, of course, be the well-lit side, and the side, or hemisphere, away
from the beam of light would be the dark side. As to how exact the division between light
and shadow would be, one has to consider a number of factors. The most important are
surface roughness on the sphere and the wavelength of the light. If the surface of the
sphere is quite rough then you would see a rather fuzzy line between light and shadow.
When dealing with light, distances shorter than a wavelength of light, which is quite
short, cannot be distinguished. Hence, even if the sphere were "perfectly
smooth" the division between light and dark wouldn't be more "exact" than
to within a wavelength of light. But since a wavelength of light is a fraction of a
millionth of a meter, being within a wavelength of light is still pretty good. Finally, I
am not certain what you mean by "reactions" that may be taking place at the
"border." Nothing particularly unique or interesting would necessarily occur on
the light/dark border. Of course, anytime light interacts with matter, something happens.
Whether it is scattering, reflection, refraction, dispersion, or absorption, the light and
the matter interact in many complex and interesting ways. The fact that these processes
may be occuring near the edge of a shadow is largely irrelevant, however. I hope I got at
what you wanted to know. Let me know if I goofed anything up and I will see what I can do.
By the way, when Professor Biermann speaks
up melting an 'ice cap' you musn't assume that the ice is necessarily made up of water as
we usually assume when we talk casually about 'ice'. The polar caps may be made up, for
example, of carbon-dioxide 'ice'. See a previous posting on this list about 'Water on
Mars' for more details.
Actually, there are 2 types of amnesia: antergrade & retrograde. The former is associated with Alzheiemer's disease, certain other brain dysfunctions, and certain types of rare neurosurgical procedures. It involves normal memory for old (pre-trauma) events but a lot of difficulty in remembering stuff that happened recently. For example, a newspaper may be re-read several times a day, with each reading a "new" experience.
x = x0 + v0x(t)
y = y0 + v0y(t) - (1/2)g(t*t)
where
x is the horizontal position
y is the vertical position
t is the time after the arrow is released or fired from the bow
x0 is the initial horizontal position
v0x is the initial speed in the horizontal direction
y0 is the initial vertical position
v0y is the initial speed in the vertical direction
g is the accelceration on the arrow due to gravity
There is another point that is important too. There are two parts to any shadow. In one part of the shadow, the light source is completely blocked. It is fairly limited in size and is called the umbra. In the much larger part of the shadow the light source is only partially blocked. This part of the shadow is called the penumbra. The effect of the penumbra is so small that it is often not even noticed when one is out in the sun. The penumbra of a tree provides little shade. One must be in the umbra to actually feel like one is in the shade, that is, in the tree's shadow.
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![[Photo of Shadows]](shadow.jpg)