- Ask a Scientist! -continued-
Carole Milner, a college student, asks:
What is the difference between hair and fur?
Rick Lampe, a biologist, replies:
In a technical sense, fur is a type of hair. Mammals are the only vertebrates
with hair. Hair, however, serves various functions and so appears on mammals
in various places and in varying thickness. The so-called fur, is made up of
thick insulative soft hairs, called "under-fur" that trap air in an insulative
layer around the body. The longer hairs, called guard hairs, are protective of
the underfur. They also provide the color pattern of the organism whereas the
underfur lacks as much coloration. Underfur is common in mammals living in
temperate to polar climates. It may be shed during warmer seasons.
Hope that this answers your question.
A. NONYMOUS, a teacher, asks:
What is a molecule? I know the book definition,
but it's hard to explain that to a beginner student
of science. Can you break it down into terms that
a young mind can understand?
Jon Hutchins, a chemist, replies:
A molecule is made up from two or more atoms. For example, a water molecule has
one oxygen atom and two hydrogen atoms joined to it, one on each side. So what
is an atom? Basically it represents the smallest possible amount of an element,
of which about 90 exist in nature. As an analogy, what is the smallest
population of people (other than zero) which can exist somewhere? Answer
one,right? What is the smallest amount of an element? Answer: one atom. Half an
atom is no longer an element, just as the cut-off arms and legs from a person
are no longer a person. Molecules, similarly, are the smallest possible amount
of a compound (like water) which can exist. If you cut up a water molecule, it
is no longer water.
Michele MerrillFro, a middle school teacher, asks:
Originally from a student: How many elephants are there in
the world? (they didn't specify type, or captivity status)
Which animal is the most endangered?
Thank you!!
Jack Mellen, an animal ecologist, replies:
Estimates of elephant populations are not very accurate. A most conservative
approach estimated African elephants at about 300,000 in 1990. However other
estimates for the same year suggest possibly as many as 600,000. Regardless,
there has been a significant decline in populations of African elephants since
1980 when their number was estimated at 1.3 million. The population of Asian
elephants in that same year was 40,000 of which as many as 13,000 were
in captivity.
John Traylor and Jen Pol, high school students, ask:
What happens to the alpha particle after alpha decay? How can you have
an anti-neutral particle (antineutrinos)?
Joe Traylor, a physicist, replies:
1. In alpha decay a single particle composed of two protons and two neutrons
is emitted from the decaying nucleus. The particle is, in fact, identical to
the nucleus of a helium atom. On decay, the alpha comes flying out of the
decaying nucleus at very high energy (usually). It travels until it collides
with something --anything-- in its way, most often another nucleus or atom.
Because the alpha has so much enegy AND two positive charges, it can and does
rip the electrons off the atoms it collides with. The electrons are
attracted
to the doubly charged alpha and try to follow it in its path. This effect is
why alphas are so destructive; they rip electrons off --that is, ionize--
many
atoms in their path, leaving the atomic (chemical) structure of the material
damaged.
Finally they run out of energy from all those collisions. That allows
the
elctrons to "catch up" with them, and two will join them and form a neutral
helium atom inbedded in the material.
2. Yes, the term antinetrino does strike confusion in many people. How about
anti-photon? that one is just as hard to understand! The explanation is
becuase the term "anti" is applied to several attributes of particles, not
just
charge. For example, you may have heard of the attribute "spin" as described
for particles. The name came from a simple model of thinking of the particle
as
spinning like a top. Turns out that the amount of "spin" a particle can have
is
quantized, that is, a definite quantity or amount. In fact, it's so
important
that all known particles are described to have spin in either half- or whole-
single units of exactly the same amount of angular momentum or spin.
Particles
with 1/2 units (electrons, protons, neutrons, etc.) behave one certain way
and
the integer, whole unit ones behave VERY differently. The very amazing
property
of superfluidity results because the helium atom acts as a "whole-spin"
particle.
At any rate, we see that there are several other properties than charge.
Antiparticles can have the opposite of any of these attributes. Example: the
neutrino and the anti-neutrino have opposite spin. As they move in space
they
"spin" oppositely: one clockwise (so to speak) relative to the motion, and
one
counterclockwise.
Thanks for your very important question! I hope you will study it
further;
this gets just plain exciting the more you are able to understand.
Todd Mackey, a high school student, asks:
In class we were talking about the four phases of matter. As
you know, the particles, even in a solid, are still moving to
a certain extent. A student asked, "If we ever reach
absolute zero where all movement of particles stops, will this
create a fifth phase of matter or will it still be called a
solid even if the particles have stopped moving?"
Mark Biermann, a physicist, replies:
First of all, be prepared for the kind of answer that some people find
frustrating in that I am not actually going to answer the question that was
asked. The reason for this "sidestepping" is straightforward and is this:
it
is dificult to speculate about what will happen to matter at absolute zero
because, to the best of my understanding of physics, it is impossible for
matter, or anything quite frankly, to exist at absolute zero. The reason for
this is all wrapped up in relativity and quantum mechanics. So, since I'm
not actually going to answer your question, I should at least let you know
why it is effectively unanswerable. Here goes.
As you pointed out in your question, all matter is still moving, even if
it is in a solid. The individual atoms that make up the solid are vibrating
about their fixed, average position within the solid. The warmer the
temperature of the solid, the stronger are these vibrations. Obviously, as
a material reaches absolute zero these vibrations would have to stop. Any
motion at all would indicate the presence of heat energy, which is
inconsistent with being at absolute zero. But it is this requirement for a
complete lack of motion that leads to a complication. One of the most
intriquing aspects of the theory of quantum mechanics is Heisenberg's
uncertainty principle. This uncertainty principle is widely misunderstood
and misapplied, but it is of great relevance in the present context. The
most
basic form of the uncertainty principle establishes a relationship between
the
position of an object, such as an atom, and its momentum. In essence, the
result is that if one of these quantities is known exactly, we can know
nothing about the other quantity. Now look at this result in reference to a
material at absolute zero. If we can stop all the motion of the matter then
we know its momentum exactly. That is, since momentum is defined as mass
times velocity and the velocity of a stationary object is zero, the momentum
of matter at absolute zero is zero. But if we know the momentum of the
matter exactly, we know nothing about its position. The matter could be
anywhere in the universe. This makes it difficult to measure the temperature
of the matter in question. In short, quantum mechanics leads us to the
result that the Heisenberg uncertainty principle precludes the existence of
matter at absolute zero because absolute knowledge of momentum leads to
meaningless information about position.
One other point is worth mentioning. You might want to think about the
role of relativity in all of this. According to Einstein's theory of special
relativity, matter is just another form of energy. So, if matter is present,
energy is present. But energy is exactly what we can't have around if we
want to lower the temperature of an object to absolute zero. Now we are
really stuck. If matter is energy, and the presence of energy means the
matter is not at absolute zero, then the only way to get the matter to
absolute zero is to remove all of the matter. Given this problem, and that
arising in the context of quantum mechanics, one can see why any ideas
concerning the phase of matter at absolute zero is pure speculation and
probably not of much value.
Joe Traylor, a physicist, also replies:
Todd, there is another way to think of absolute zero: not that it
it means that there is *no* energy left, but rather than it means
there can be no more energy *removed* from the material. Becomes a
"ground state of energy" rather than "no energy."
In fact, you are already familiar with thinking this way. You
commonly think about the ground state of an atom as having the
electrons in the lowest possible energy state. You certainly did not
think the electron was sitting still in the atom!
Absolute zero is like that. Even at absolute zero, the electrons
in an atom would still be orbiting the nucleus, so there would still
be motion! True, there be no motion of one atom relative to its
neighbor, but inside the atom itself there's lots going on. Even at
absolute zero.
Megan Olerich, a middle school student, asks:
What are your feeling about the hole in the Ozone
Layer and how it is slowly getting bigger?
Jon Hutchins, a chemistry professor, replies:
The latest I have read about ozone depletion in the upper atmosphere is that
the rate of loss of ozone seems to be slowing down. If this is true then the
Montreal Protocol (an International Agreement banning CFC use) is having some
effect. However, other things beside CFCs may continue rising. Also, the
estimates for complete restoration of stratospheric ozone without any new
ozone-depleting agents being added to the atmosphere are of the order of 100
years.
Thanks for submitting your question. I look forward to addressing any more
questions you may have on this or other subjects.
Wind Goodfriend, a college student, asks:
The question is: A long time ago I heard that when shuffling a deck of
cards,
it takes exactly seven shuffles to fully randomize
the deck from where it started . Is this true?
By "shuffling," I assume he/she meant the standard way of
cutting the deck
into two sections and "bridging" them back together. Thanks!
Tim McDaniel, a mathematician, replies:
What a great question! Let's assume that when you shuffle a deck
of cards, you are mixing them up "at random," with nothing systematic
or planned going on. So the cut of the cards and the subsequent
shuffle is imperfect and, therefore, pretty much random.
It is not really technically true that "...it takes exactly seven
shuffles to fully randomize the deck from where it started." Instead,
it has been determined that one shuffle mixes ("randomizes") the cards
up pretty well, two shuffles mixes them up better, three shuffles a
little better, four a little better, etc. By the seventh shuffle, the
deck is mixed up pretty darn well. In fact, while any number of
shuffles greater than seven will mix the cards up a bit better (make
it a bit "more random") than otherwise, this increase is teeny-tiny
and insignificant. In fact, if you add up *all* the improvements you
get from the eighth shuffle on, even this "sum of improvements" is
teeny-tiny and insignificant and not worth the effort of the extra
shuffling.
The researchers figured this out by using a technique called
"Monte Carlo Simulation." Instead of actually physically shuffling
cards, or working out 100 percent of the surprisingly complex and
way-nerdy math involved, they empirically observed how the cards get
mixed up when a deck is shuffled in a typical fashion. They then
programmed a computer to simulate this shuffling, and let it run for a
while and perform thousands and thousands of sets of simulated
shuffles. For each set of shuffles, the computer evaluated and
recorded how "random" the cards were after the first shuffle, the
second, the third, etc. They then used this data to generalize how
random the cards would typically be after a first shuffle, a second
shuffle, blah blah blah. The rationale behind this is that if you (or
a computer...) try something a ton of times and pay attention to what
happened, then you're going to end up having a pretty good idea how
the something works in general.
From a theoretical (and therefore, pretty cool if you're a math
nerd like me) perspective, as the number of shuffles approaches
infinity the deck approaches being truly "fully randomized." But in
the real world, seven shuffles is good enough. After seven shuffles
the "Law of Diminishing Returns" kicks in to such a great degree that
the benefits of additional shuffling are not worth the cost of
physically doing the shuffling.
This rule does not apply to hustlers/magicians who can shuffle
decks of cards systematically. For example, a few magicians/hustlers
can perform a "perfect shuffle," where the cards are shuffled together
*precisely* and *always* one-at-a-time. That's not random; it's
systematic! After a few perfect shuffles (sorry, I can't remember the
exact number required) the deck is back to where it originally began!
Pretty nifty, huh? I know two expert card manipulators (one fellow
math/stat geek colleagues and one magician) who can do this. They're
way-cool people, but I'd never play poker with either of them.
By the way, this was discussed in surprisingly long article in
the New York Times a few (6 or so) years ago; these same general
results were cited, without some of these details. Of course, since
it was in the NY Times, it *must* be true! QED ;)
Mark Ciagne, a college student, takes issue with our answer to the riddle
below:
In response to the riddle about Art. The point in which you
know he is lying is when he said he was tracking a polar bear in the dead of
winter.
Everyone knows bears are hibernating in the winter.
Our ever patient cadre of Scientists replies:
Not so, Mark! Polar bears spend most of their time on the drifting pack ice,
feeding and resting, but (except for pregnant females) spend only brief
periods in their dens unlike most northern climate bears.
The
pregnant bears come ashore to dig their dens in November, then give birth to one or two tiny cubs in December or January. The mothers nurse and care for the
young until March or early April, when they emerge from the dens. After several days getting used
to the outside environment, including short trips to strengthen the cubs, the families leave the dens.
They move back to the sea ice to hunt ringed seals and other prey. The cubs stay with their
mothers, learning to hunt, for about the next two and a half years. So, in all
likelihood the polar bear Art Bragg tracked and killed was either male or a non
pregnant female.
The BVU students in Heritage Hall riddle us thusly:
Art Bragg claimed that, while on an African safari hunting a
vicious lion, he slipped and broke his foot. Not to be put
off, he managed to continue on long enough to track the lion
and kill it. Then he said that while he was at the North
Pole during the dead of winter, he caught a terrible cold,
but was still able to track and kill a polar bear. Then,
to top it off, while in a small boat off the coast of
Florida, he was able to catch and land a shark, in spite of
the fact that his arm was badly sprained. Although Art's
tales are hard to believe, on what point do you know he's
lying?
Our staff replies:
Nice attempt to trick us! Less experienced scientists might fall for your
trap and argue that 'you can't catch a viral cold at the North Pole' but we
know better! True, Art Bragg probably wouldn't catch that cold from
smooching a polar bear but he might very well catch it from an amorous
encounter with a fellow member of his party who brought the cold along
with her. The cold virus can survive quite handily inside a warm
body. Our conclusion? Art Bragg may very well be telling the truth!
A BVU student asks:
What are Napier's Bones and how do you use them to do division?
Ken Schweller, a computer scientist, replies:
Well, we are going to cheat on this one . It so happens that 'Dr.
Math' at Swarthmore College has recently addressed this same question. You
can see what he had to say by clicking
here.
Thomas Schunk, a BVU alumnus (1990), asks:
Lets say that you are traveling in a car at the speed of
light and you turn on the headlights, what happens? Also what happens when you
beep the horn? Also, what happens if you hit a deer? Does the deer ever see
the headlights before it gets hit?
Mark Biermann, a physicist, replies:
Questions concerning the speed of light are at the heart of the
Special Theory of Relativity, as first described by Albert Einstein early
in this century. Before dealing with the "what if's" concerning a car
traveling at the speed of light, it is worthwhile to make it clear that, to
our best understanding of the physical world, it is impossible for a car
to travel at, or greater than, the speed of light. As a matter of fact, in
our current understanding of the physical world, it is impossible for
any matter to achieve a speed greater than or equal to the speed of light.
So, while the USS Enterprise of Star Trek fame uses "Warp Drive" and
"Subspace" to get around this speed of light barrier, and the Millenium
Falcon of Star Wars fame uses "Hyperspace" to do the same, we mere mortals
on present day earth or stuck with the ultimate speed limit, the speed of
light.
One more preface to answering the core of your question. The "speed of
light" can be somewhat ambiguous. When someone talks about the "speed of
light" being faster than any matter can travel, the individual means, or
should mean, the "speed of light in a vacuum." The speed of light in a
vacuum is about 300,000,000 meters per second. This quantity, usually given
the symbol "c," is the ultimate speed limit I referred to earlier. The
speed of light is actually lower in any material. While light travels only
slightly slower in air, in glass light is traveling at about 200,000,000
meters per second. In a diamond, light is traveling at only about
120,000,000 meters per second. (There is one type of material in which
the speed of light can be great than its vacuum speed, a highly ionized
gas called a plasma, but I won't get into the details on that.) So keep
in mind that whenever I say the "speed of light" I mean the "speed of light
in a vacuum."
The Special Theory of Relativity states that no matter what, the speed
of light in a vacuum is a constant. This makes it different from other waves
and matter. Say you are in a car and you throw an apple core forward. The
total speed of the apple core would be the speed of your car, plus the
speed of the throw. Not so with light. Independent of the speed of the
source, light will travel at c, the speed of light in a vacuum. So, if a
hypothetical car were traveling at the speed of light, flipping on the
headlights would do nothing to help visibility. The car would be traveling
as fast as the light and the light would never "leave" the headlights. The
poor deer who is about to be clobbered would receive no warning at all.
Without warning, it would be pulverized by a car traveling at an incredible
rate of speed. The light being produced in the headlights couldn't outrun
its source and so the car and the light would arrive together. Frankly,
if the deer has to go, it is probably just as well that it doesn't know the
car is coming.
As far as what happens with the sound from the horn, it is worth noting
that sound needs a medium to travel through. So, while light will travel
through a vacuum, sound will do no such thing. Sound needs something
to travel through; air, water, rock, etc. Assuming that this hypothetical
car is somehow going at the speed c through a hypothetical medium that would
carry the sound waves, the sound waves could propagate away from the car. Since the speed of sound in air is about 344 meters per second, or about
1 million times slower than c, the car is obviously traveling faster than
the speed of sound. The people inside the car would probably not hear
the horn, since they would outrun the sound. People in front of the car
would certainly not hear the sound until long after the car had gone past.
The same applies to people on either side or behind the car. But in
actuality, no human would probably be able to hear the sound. Due to
the high rate of speed of the car, the sound of the horn would undergo a
Doppler shift that was so great that the sound would no longer be audible
to humans. Maybe a dog might be able to hear it, but that is a subject for
another time.
Judy Ferguson, a parent, asks:
During the winter after an ice storm, how come when a bird
lands on a telephone wire it doesn't twirl around on the wire?
James Hampton, molecular biologist, replies:
Because birds tape sandpaper to the bottom of their feet in the winter?
Jack Mellen, an animal ecologist, replies:
The physics of this have to do with keeping the center of mass in proper
alignment with the center of balance or center of support. If the two
become misaligned a torque is created that will tip a bipedal organism over.
The physics of this should be addressed by a physicist.
When standing, birds and other bipedal organisms keep from falling over by
constantly readjusting their centers of mass to be over their centers of
balance. (They do this by sensing that they are in fact falling over--a topic for another
question.) Birds do this primarily by moving their necks. Among vertebrate
animals, bird necks are relatively long compared to their body lengths. This
may be an adaptation to their bipedalism. By moving their heads and necks they
shift their weight and realign the two centers.
An interesting counter question is how does one know that birds don't lose
their balance? If they fall they are likely to just look like they are taking
off!
And by the way, I have seen several dead, apparently lightning struck
blackbirds twirled under the wire indicating perhaps that only live birds are
capable of maintaining their balance!
Paige Havens, a grade school student, asks:
Why do spinning tops not fall down?
Joe Traylor, physicist, replies:
Paige,you've asked a very advanced question! And, although it's
such a common event that spinning tops don't fall, it's not at all easy to
understand. But let's try.
First before we think about spinning, think about objects moving
straight ahead, like a car or a bicycle. They are hard to stop --even
harder when they are heavy or moving very fast. Physicists call the
property of their motion "momentum," and heavy objects moving fast have a
lot of it. To stop the object, you have to remove all that momentum.
Spinning objects have another *kind* of momentum, namely "angular
momentum" from angular or rotational --spinning-- motion. Think of the
merry-go-round on a playground: get it going fast (rotational speed) with
lots of kids on it (heavy) and it's hard to stop because it has so much
angular momentum. A spinning top has lots of angular momentum.
Now comes the interesting part. If the top is leaning as it spins,
it has a natural tendency to lean further due to its weight. But, because
of its angular momentum, the weight pulling down makes it *rotate* rather than
fall! That is, the new motion, instead of falling, is to rotate! push it
down, and it moves forward! Try to lift it, and it will resist you!
Here's why: trying to change angular momentum by pushing in a certain
direction *always* causes a change to the side rather than in the direction
you push. (The fancy word for "to the side" is "perpendicular.")
Angular momentum is a very interesting subject. It's the basis of
why gyros work to help steer airplanes and ships, it keeps the Earth always
lined up with the North Star at "north," and it helps atoms line up beside
each other in certain arrangements.
An anonymous reader asks:
So--how come I can't ask a psychologist? If they promise
not to use a couch, don't they count as scientists?
Ken Schweller, computer scientist AND psychologist replies:
Your point is well taken! Experimental psychology is of course a science on
equal footing with the so called 'natural sciences'. Interestingly enough, if
we
reserve the word science for disciplines that employ the so called 'scientific
method' of hypothesis and experimentation then there are clearly two imposters
on
our list - computer science and mathematics. Neither relies on hypotheses,
experiments, data collection, and statistical analysis as their key methods of
investigation.(Someone else once quipped 'any field that attaches the word
science to itself probably isn't'.)
So, the reason computer science and math
are 'in' and 'psychology' is out is due strictly to the historical makeup of
Buena Vista University's Science Department. The folks listed are just those
that are currently members of that School of Science. Arguably, a better name
for our list might have been 'Ask a member of the School of Science', but, hey,
that doesn't sound half as cool.. Thanks for writing.
- Robbie Schweller, a high school student, asks:
If sound is just air waves that hit your ear and light is
waves too how come we can hear around corners but we can't
see around corners?
- Physicist Mark Biermann replies:
While sound waves and light waves are both "just waves," they are about
as different as two waves can get. Sound is a longitudinal wave, vibrating
along the direction it travels, and light is a transverse wave, vibrating
at 90 degrees to the direction of travel Sound requires a material to travel
through, such as air, steel, water etc. As a matter of fact, the more dense
the material, the better sound travels through it. So, sound travels faster
and with less loss through a steel rod than it does through air. Light on
the other hand can travel through a vacuum. Light does not require a medium
to travel through, which is why the light from the sun reaches us here on
earth even though it has to travel through over 100 million kilometers of
vacuum to do so. As a matter of fact, light travels best through a vacuum.
The speed of light is at its maximum value in a vacuum and its losses are
minimized in a vacuum.
All of which does not really answer your question. The answer to your
question lies in another difference between light and sound. The wavelength
of sound is much greater than that of light. Audible sound has wavelengths
in the range of about 1 meter. Visible light has a wavelength in the range
of one half a micron, where a micron is .000001 meter. Why does the
wavelength matter when it comes to hearing a sound around the corner?
Because we hear sounds around a corner due to an effect called diffraction.
Diffraction occurs whenever a wave passes through an opening or around a
barrier. When a wave diffracts, it no longer travels in a straight line,
but bends and curves and starts traveling in new directions. Which is the
key to hearing a sound around a corner. As the sound wave passes around
the corner, it diffracts because the corner acts as a barrier. The diffraction
effect at the corner causes some of the sound waves to "bend" and travel
down the hallway or street or whatever is perpendicular to the initial
direction of travel. So you hear the sound around the corner because
the sound wave diffracts as it passes around the corner and gets redirected
onto new paths.
So why doesn't light also get diffracted as sound does? Because of
the wavelength difference. It turns out that diffraction effects are the
most strong for a particular wave when the opening or barrier is about
the same size as the wavelength of a wave. Thus, everyday openings such
as doors, entrances to hallways, etc., are the perfect size to cause
dramatic diffraction effects in sound waves. With a wavelength on the
order of 1 meter, a doorway that is 40 inches wide is a great diffractor.
However, a 40 inch door way is a very poor diffractor of light. The
bending and redirecting due to diffraction will be about 1,000,000 times
weaker for light due to the very short wavelength. In order to see much
diffraction of light, one must use an opening that is about the same size
as the wavelength of light. Such objects are manufactured to have very
narrow openings and are referred to as diffractionn gratings. As you
would probably guess, an opening of about .01 mm does a pretty good job
of diffracting light, but a horrible job of diffracting sound.
Note the diffraction of light is a rather complicated effect and that
in order to see any kind of quantifiable diffraction effect, one usually
has to use light from a laser or another special source. The "why" on that
will have to wait for another time.
Bottom line: Sound is diffracted strongly by everyday objects because
of coincidence of nature that makes people use doors that are about the
same size as the wavelength of sound. Here's one to think about: Radio
waves can have wavelengths of about a meter. Will they be strongly diffracted
by a doorway?
If you have any questions, just post another request and I will answer it
as soon as I can.