Rio Americano High School Physics
Show & Tell Demonstrations
Presented by Dean Baird
at Meetings of the Northern California/Nevada
Section of The American Association of Physics Teachers
"Science Standards Alert," April 1997
WILL YOUR STUDENTS PASS THIS TEST?
1. The internal motion of atoms within matter is kinetic energy,
which we observe as
I. Heat.
II. Sound.
III. Internal Energy.
A. I
B. II
C. III
D. I & II
E. II & III
F. I, II, & III
2. (True or False) Radio waves have kinetic energy.
3. Electric current is
A. the rate at which electric charge flows.
B. a flow of energy due to the motion of electrons.
C. whatever you want it to be, based on your own personal feelings
and experiences.
D. whatever the Standards Committee in your district says it is.
"CORRECT" ANSWERS:
1. D
2. True
3. B
This is my interpretation of of the Draft Physical Science
Content Standards being developed by WestEd. I've listed the
specific standard below.
K-12 Concept 3A
Any moving object has kinetic energy. The internal motion of atoms
within matter is also kinetic energy, which we observe as heat
or sound. Temperature is a measure of the average kinetic energy
per molecule in matter. All forms of radiation (e.g., light, radio
waves) have kinetic energy. Electric current is a flow of energy
due to the motion of electrons.
"The Laser Beam Viewing Tank," November 1996
Construction Instructions.
Suggested Demonstrations
Fill the tank to a 5" depth of water. Stir in a small small
sprinkle of a few flakes of powdered milk. Be conservative on
that powdered milk; you'll tend to add too much. You need enough
to scatter the laser beam but not so much that the beam is diffused
before getting across the tank.
1. See the Light
Shoot the beam through the tank and marvel at the visible beam.
2. Refraction
Aim the laser beam downward toward the air-to-water boundary at
a convenient oblique angle of incidence. The laser angle and the
beam (in the water) don't match!
3. Total Internal Reflection
Aim the laser upward toward the water-to-air boundary. Marvel
at the splendid TIR.
4. "Optical Fiber"
Vary the angle of incidence in the demonstration above. The kids
really dig this one.
5. Gradual Refraction
Drop a layer of sugar cubes in the tank and let them dissolve.
Do not stir. Send the beam through the tank and observe
gradual refraction due to the index gradient.
6. Diffraction
Tape a diffraction grating to the side of the tank. Shoot the
beam through the grating and marvel at the three or five beams
that emerge in the water.
7. Whatever else you can think of...
"Physics
is a Mind-Expanding Subject (Illusion)," April 1996
This is a lecture hall version of a demonstration from The
Exploratorium's Science
Snackbook. This large audience version was presented to
me by fellow SCAMPI mentor Dennis Hudson. A printed or drawn spiral
pattern is attached to an electric screwdriver and spun like a
propeller in front of the instructor's face. The instructor allows
the pattern to spin for 20 seconds or so, then abruptly moves
it away and stands stone-faced before the class. The audience
will see the instructor's head expanding or contracting depending
on how you spun the pattern. Expanding is better. Very Dramatic!
Don't try to "enhance" the effect by making a funny
face (it won't work). And don't move. The motionless stone face
is all you will need.
"The Photoacoustic
Effect," November 1995
Again, a demonstration with SCAMPI origins. You need a photographic
flash unit (or camera with a flash unit). Listen to the sound
of the flash when it goes off. Not much sound there. Now hold
it against a dark (preferably black) fabric and listen to the
flash. Wow! Try it against something white and shiny. Hmm. You
may not believe the results or the explanation. The explanation
is that black, coarse surfaces absorb more radiant energy than
light, shiny ones do. As a result, dark materials undergo a rapid
increase in temperature and a correspondingly sudden thermal expansion.
It is the rapid expansion that causes the relatively loud sound.
"The Paper
Magnet," April 1994
Orient a piece of 8.5"x11" paper horizontally (landscape).
Now divide it into four equal horizontal lanes (this can be done
by folding it in half twice). If the top lane is #1 and the bottom
is #4, then write N's and S's in the lanes as follows. In lane
1, put an N and an S at opposite ends. Leave lane 2 blank. In
lane 3, put an N, S, N, S (the first N is at the left end, the
final S is at the right end, the center S and N close to each
other in the middle. In lane 4, it's N, S, N, S, N, S, N, S. Now
fold it in half and half again (the long way) so that lane 1 and
lane 2 are on the outside (showing). You can rip it in half so
that you have two monopoles showing. But if you hold one half
so that a "monopole" is showing and refold it, an N
and S appear. Your audience will feign amazement. Explain that
you can cut the magnet as many times as you want, but you'll never
get a monopole. Rip the paper magnet your holding in half and
flip the halves over, revealing two N-S paper magnets. This always
seems to get a reaction as if you did something truly magic!
By the way, Ann Hanks of American River College reports that the
magnetizers manufactured by Electro Technical Products (and sold
by the big supply houses) are wired backwards. The hole into which
you're instructed to place the north pole of your magnet
will magnetize south and vice versa. When she called to
report this to the manufacturer, they responded that this is done
so that customers' newly induced magnets will have north poles
that attract the north ends of compass needles. When their devices
were wired correctly, they say, customers complained that their
north poles attracted the south end of compass needles. This is,
of course, what they should do. Ann suggested we might contact
ETP to share our professional opinions with them. Their phone
number is (312) 561-2349 and their FAX is (312) 561-3130. Their
snailmail is 4642 North Ravenwood; Chicago, IL 60640-4592.
"Aristotle's
Statement of Newton's First Law," November 1993
This was presented as a multiple choice question. The audience
was allowed to guess who (Aristotle, Galileo, Newton, or Andria
Erzberger) said: "It is impossible to say why a body that
has been set in motion in a vacuum should ever come to rest; why,
indeed, should it come to rest at one place rather than at another.
As a consequence, it will either necessarily stay at rest or,
if in motion, will move indefinitely unless some obstacle comes
into collision with it." Believe it! Or read Physics,
Book IV, Chapter XI for yourself. Aristotle was actually arguing
against the possibility of a vacuum in this context, not eloquently
characterizing the nature of inertia. Nevertheless, it brings
to mind Alfred North Whitehead's assessment that, "Everything
of importance has been said before by someone who did not discover
it."
"The Newtonian
Shot: A Dart Gun Demonstration," April 1993
Start with two toy dart guns (the REAL ones with hard-stem darts,
not those floppy "safety" darts). Tape a marble-sized
lead weight to a suction cup on one of the darts. Now load the
two guns: one with a regular suction cup dart, the other with
the weighted dart. From a significant height, aim both guns toward
the ground and fire them simultaneously. It's best if you poll
students before carrying out the demonstration. The surprising
results should catalyze a healthy discussion on Newton's second
law.
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Copyright 1999 by Dean Baird. All rights reserved