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BALLOON DEMONSTRATIONS, science classroom
Physics Instructional Research Association, PIRA

From the PIRA FTP site at
ftp://ftp.phys.ksu.edu/pub/pira/news+info/balloon.txt

Collected from the TAP-L discussion group (Teaching Apparatus in Physics) tap-l@listserv.appstate.edu

Info:
http://www.wfu.edu/physics/pira/tapl/PIRATapL.html about TAP-L forum
http://listproc.appstate.edu:8000/guest/listutil/TAP-L Archive


Date: Wed, 15 Feb 1995 13:04:37 -0500
From: MAIULLO@r***.edu
Subject: Balloon Demonstrations

Hello fellow Tap-ler's:

I'm doing a demonstration show on friday night, and I wanted to do a series of demonstrations using balloons as the basis for each one. Example: Balloon in bell jar, pull vaccuum, watch expand. or, balloon in liquid Nitrogen, etc.........

Does anyone out there have a demo that they think is really neat using a balloon? Either post it here, or, send it to me direct at maiullo@r***.edu,. I have about 10 or so already in mind, and would love to see some novel ideas come through the network. Wouldn't make a bad article, once I got them all collected, would it Roger?

Thanx again,
Thanx in advance,
David M.




Date: Wed, 15 Feb 1995 13:27:08 -0500
From: "Lecture Demo" brett@w***.edu
Subject: Re: Balloon Demonstrations

Dave -

How about the water balloon heat capacity demo?  Fill a balloon with
water and hold a lit match or candle up to the surface of the balloon.
It will easily withstand the flame because of the high heat capacity of
the water.  You can even hold it over your head while you torch it if you
want some drama.  A candle or match works best since it burns cooler than a
butane lighter; you can use a lighter but it will sometimes burn through
after prolonged heating.  Use a good balloon and fill it pretty full so
that the skin is stretched thin, but if you get soaked I don't want to
hear about it.  Wouldn't mind seeing it, though.

                                                     Brett




Date: Wed, 15 Feb 1995 13:49:23 -0500
From: FNILON@P***.EDU
Subject: Re: Balloon Demonstrations

Dear Dave:

        Balloon electroscope:  charge 2 balloons on opposite ends of a string
and hold the string in the middle.  Charge a balloon and put on the wall,
podium, or whatever.  You can also raise a little hair holding a charged
balloon over someones head.

        Change of phase in CO2:  Place a small pellet of dry ice in a small
test tube and cover the top with a balloon (deflated).  Inflate the balloon by
warming it in you hands until the dry ice has sublimated.  Immerse the test tube
in liquid nitrogen and dry ice will form on the sides of the test tube and the
balloon will deflate (and sometimes get sucked into the small test tube.

                Best wishes on you lecture
                Frank N.
                Pomona College




Date: Wed, 15 Feb 1995 14:38:07 -0500
From: William Beaty 
Subject: Re: Balloon Demonstrations

BALLOON-COATED BOTTLE INTERIOR:  I recall a demo in T.P.T. where a balloon is
quickly stretched across the mouth of a flask containing a small amount of
rapidly boiling water.  The flame is then removed, and as the flask cools,
the balloon is sucked entirely inside until it "coats" the inside of the
flask.  When offered as a pre-made item, the balloon-coated flask is
immensely befuddling.  How the heck did that balloon get in there?!!!

William Beaty  voice:206-762-3818
EE/Programmer/Science exhibit designer        http://amasci.com/
Seattle, WA 98117                             SCIENCE HOBBYIST web page





From: Steve L. 
Subject:      Re: balloons tricky problem

   If we assume that the balloon is moving slowly near the surface of the
planet, where the gravitational field (measured by g) is uniform, the
density of the atmosphere is constant, and the effects of air resistance
are smaller than the buoyant force, then the upward acceleration of the
balloon is proportional to g.

   Let m = mass of the rubber balloon itself, V = the volume of the balloon
(assumed constant), d(air) = density of the atmosphere, and d(gas) =
density of gas inside the balloon.  Then the downward force on the balloon
is mg + d(gas)Vg, and the upward buoyant force is d(air)Vg.  The upward
acceleration then turns out to be

        a = ((d(air) - d(gas))V - m)g/(m + d(gas)V)

(Too bad we can't write proper equations on the net...)  Anyway, if
air resistance is neglected, the upward acceleration is proportional to g,
and a balloon will rise more slowly if g is the only thing that changes.
Even allowing for a lower atmospheric density as a result of a smaller g,
the upward acceleration decreases with decreasing g.  I haven't worked out
the case with air resistance yet.




Date: Wed, 15 Feb 1995 14:38:36 -0500
From: William Beaty 
Subject: Re: Balloon Demonstrations

Here's one from Daedalus in Britain: a cardboard box which is not stable,
and falls over, even though it is a perfect cube.  In reality, the box is
brown paper stretched on a frame, and has a large helium balloon in one
side, so that it's center of gravity is shifted to OUTSIDE the base of the
box.

Another: creating neutral density with carrots and duct tape.  Tie a stick
of carrot (etc.) to a helium balloon, and eat it shorter until the balloon
just hangs in the air without rising or falling.  If you bite too much,
add weight by sticking patches of duct tape to the balloon.  A roomful of
these is great fun.  If you make a custom mylar-bag balloon, fill it with
helium, then cover it with duct tape until it's buoyancy is neutralized,
you can play catch with it and show that air has considerable mass even
when weightless. 

Here's one that a friend found: SOUND LENS.  A balloon acoustic lens. 
Normally a balloon is under pressure and has a higher index of acoustic
refraction than the surrounding air, so it bends sound waves and behaves
as a lens.  Sound from distant sources will be focused behind the balloon. 
Practice with a balloon and a microphone, and you'll soon be able to
listen in on distant conversations. Use a balloon and a tiny loudspeaker,
and you'll be able to project a sound beam to an individual listener. Blow
up your balloon so the rubber is really tight, this compresses the air
more. 

William Beaty  voice:206-762-3818
EE/Programmer/Science exhibit designer        http://amasci.com/
Seattle, WA 98117                             SCIENCE HOBBYIST web page





Date: Wed, 15 Feb 1995 14:46:21 -0500
From: EBERT@U***.EDU (Ron E. - UC Riverside Physics Department)
Subject: RE: Balloon Demonstrations

David, how about sticking a long darning needle through a balloon without
busting it?  [go through the soft areas: through the fill-spout and the
"nipple" -bill b.]

Or a 2 to 1 mixture of hydrogen and oxygen in the balloon,
which has a tube in the stem that has a wire connected to a small
Tesla coil. The Tesla coil is turned on by a remote foot switch
(loadest bang you ever heard.)

Or tie a small weight to the end of the balloon and suspend the balloon in
an air jet, tilting the jet away from a vertical angle.

Ron E
UCR Physics Department







Date: Wed, 15 Feb 1995 14:46:45 -0500
From: cbettis@***.edu (clifford b)
Subject: Re: Balloon Demonstrations

>
While you have the dry ice and the balloon:

Put some in a balloon, tie off the ballon and weigh it on a balance,
watch the "weight" change as the dry ice sublimes. When the balloon is
fully inflated it can be used as a sound lens (I usually use a weather
balloon for this). The effect is most striking if you use a fairly
incoherent source of sound (e.g. running water).

Cliff





Date: Wed, 15 Feb 1995 14:47:31 -0500
From: EBERT@U***.EDU (Ron E. - UC Riverside Physics Department)
Subject: RE: Balloon Demonstrations

Fill a balloon with helium and tie it to a weight. Put the balloon on
a cart and then place a large bell jar around the balloon. When you
shove the cart forward, the balloon moves forward, contrary to
what you would expect.

Ron E





Date: Wed, 15 Feb 1995 14:55:06 -0500
From: Lecture Demo 
Subject: Re: Balloon Demonstrations

Dave -
Another balloon demo is the helium balloon in helium.  I do it with a
large glass battery jar.  Blow up a helium balloon so that it's buoyant in
air, then put it inside the upside-down glass jar and let it float to the
top.  Then squirt some helium into the jar until it displaces the air. 
The helium balloon then sinks to the bottom as it's no longer lighter than
the "air" in the jar.  If you pick the jar up, the balloon will float at
the bottom of the jar on the air/helium interface.  Tip the jar to let the
helium escape and the ballon rises back to the top of the jar. 

If you don't have a large-enough glass jar, you can remove one side of a
cardboard box and replace it with a piece of acrylic or other plastic
sheet.  Just make sure to seal all the edges with some duct tape etc. so
the helium won't leak too fast.

                                            Brett




Date: Wed, 15 Feb 1995 14:55:31 -0500
From: cbettis@u***.edu (clifford b.)
Subject: Re: Balloon Demonstrations

One more thing I do to explain the sound lens is use an oscilloscope
and microphone to measure the speed of sound through the CO2 filled
balloon. I then calculate the index of refraction and focal length
(at least for the higher frequencies).

Cliff





Date: Wed, 15 Feb 1995 15:03:10 -0500
From: EBERT@U***.EDU (Ron E. - UC Riverside Physics Department)
Subject: RE: Balloon Demonstrations

Expanding universe demo - connect a balloon to an air supply. As
you slowly inflate it, paint dots on it in different colors. Every dot
moves away from every other dot, emulating the behavior of galaxies
in our universe.

Ron E.
UCR Physics Department






Date: Wed, 15 Feb 1995 15:54:13 -0500
From: Richard_E_BERG@u***.edu (rb22)
Subject: Re: Balloon Demonstrations

Dave, et. al.:

For this demonstration you need two identical balloons (about 12 inch maximum
diameter models), a plastic tube a few inches long of diameter such that the
balloons can be blown up and connected over the end of the tube, and a wire
hose clamp.

Connect one balloon to one end of the tube, blow it up to about three inches
in diameter and clamp it so no air can flow out of the balloon.  Blow up the
second balloon to about six inches in diameter and slip it onto the other
end of the tube.  No air can flow between the balloons because of the hose
clamp.

What will happen when the clamp is removed:
(a) Will the smaller balloon become smaller and the larger balloon larger?
(b) Will they become equal in size?
(c) Will they stay the way they are?

Let the group vote, then perform the experiment with the smaller balloon on
top.  Suggest that the reason for the resulting effect is that when the
clamp is removed gravity pulls the air downward.  After the boos and hisses
subside, tell them the real reason, if you can think of one.

Dick B.






Date: Wed, 15 Feb 1995 16:01:46 -0500
From: chuckr@W***.edu (Chuck R.)
Subject: RE: Balloon Demonstrations

Fill a balloon with a gas that has a molecular weight greater than air.
Don't blow it up all the way.  If you leave it set, air molecules will
diffuse into the balloon and it will get bigger.

===============================================================
Charles R.
Department of Physics FM-15
University of Washington
Seattle, WA 98195
===============================================================




Date: Wed, 15 Feb 1995 16:02:08 -0500
From: William Beaty
Subject: RE: Balloon Demonstrations

On Wed, 15 Feb 1995, Ron Ebert - UC Riverside Physics Department - 909 787 5730
 wrote:

> Expanding universe demo - connect a balloon to an air supply. As
> you slowly inflate it, paint dots on it in different colors. Every dot
> moves away from every other dot, emulating the behavior of galaxies
> in our universe.

And the opposite, while not exactly a physics demo, is also fun: Totally
inflate a small balloon, then write on it in ink, in the smallest writing
you can manage.  When deflated, the writing becomes unreadably small. 
Kids can then use a 50x microscope to decode it.  Make your own microscope
slides?  Send secret messages and drawings? 

William Beaty  voice:206-762-3818
EE/Programmer/Science exhibit designer        http://amasci.com/
Seattle, WA 98117                             SCIENCE HOBBYIST web page






Date: Wed, 15 Feb 1995 16:18:02 -0500
From: MAIULLO@r***.edu
Subject: Re: Balloon Demonstrations

Everyone:  Thanx for the tremendous response to my request for "balloon"
demonstrations.  Some of them I had already thought of, but there's always
lot's of great variations in everybody's descriptions of what they do, and
some I can't wait to try.  Keep them coming!!

Dave





Date: Wed, 15 Feb 1995 16:35:11 -0500
From: William Beaty 
Subject: Re: Balloon Demonstrations

Variation on the balloon electroscope:

Add weights (carrot?) to a helium balloon to make it neutrally-buoyant (or
slightly heavy)  (in a low humidity environment) rub the balloon with fur,
wool, etc. to electrically charge its entire surface. Now each of two
"players" also uses fur to charge a spot on one or two balloons held in
the hands.  Then play slow-motion pingpong, using the neutralized balloon
as the ball. 

Something similar can be done with a single air-filled balloon and two
hand-held balloons, all which were given extreme surface charge.  Use the
two hand held balloons to levitate, or even "juggle" the single balloon. 
This can be quite hilarious, as the demonstrator gains and loses control
over the balloon, while running all over the stage and crashing into
things. 

Another one pops into mind which I have not tried.  Charge the surface of
a dark colored balloon, write a large character upon it with a dry
finger, then clap some chalkboard erasers near the balloon.  Xerography
effects will create a dark character upon a light background.

Adhere a small mirror chip to a balloon, use the mirror chip to bounce a
laser beam to a distant screen, then hum, yell, sing, etc. at the balloon.
You should get spirograph patterns as multiple resonances create Bessel-
function-type patterns all over its surface.

Hold an electrically charged balloon near your mouth as you blow bubbles
with a bubble ring, and the bubbles will end up with an opposite charge
from the balloon.  They will be strongly attracted to the balloon, and
can be held suspended by keeping the balloon overhead (at least as long
as there is no motion of the air)

Build a transparent enclosure with an open top, place a cake of dry ice
within, allow it to fill with CO2, then drop fully-inflated balloons in.
They should sit on the transparent gas.  I haven't tried this one, but it
DOES work with soap bubbles.  If balloons end up being too heavy, this
can be cured by inflating them with a helium/air mixture to lower their
densities.

Fill one balloon with helium, another with sulphur hexaflouride.  Breathe
from one to talk higher, from the other to talk lower.  If you cannot get
these gases in safe, high-purity form, then don't take any chances in
breathing them!

Draw a face upon a helium balloon, then use fur to charge only the area
of the face.  Suspend it from a string.  Do the same with a second
balloon, but hold it by hand.  The balloons refuse to speak with each
other, since the suspended balloon will rotate its face away from the
approaching charged balloon.  A "Friendly" version of this can be had by
charging the surface of the suspended balloon OPPOSITE the face, so the
face will rotate to face the oncoming hand held balloon.

William Beaty  voice:206-762-3818
EE/Programmer/Science exhibit designer        http://amasci.com/
Seattle, WA 98117                             SCIENCE HOBBYIST web page




Date: Wed, 15 Feb 1995 16:35:39 -0500
From: William Beaty 
Subject: Re: Balloon Demonstrations

On Wed, 15 Feb 1995 MAIULLO@ruthep.rutgers.edu wrote:

> Everyone:  Thanx for the tremendous response to my request for "balloon"
> demonstrations.  Some of them I had already thought of, but there's always
> lot's of great variations in everybody's descriptions of what they do, and
> some I can't wait to try.  Keep them coming!!
>
> Dave
>

Make sure to try all these in advance, since I'm just pulling some ideas
out of the air as I go along, and have no idea whether you might encounter
difficulties when you actually try to perform them! 

William Beaty  voice:206-762-3818
EE/Programmer/Science exhibit designer        http://amasci.com/
Seattle, WA 98117                             SCIENCE HOBBYIST web page





Date: Wed, 15 Feb 1995 16:36:29 -0500
From: John M. 
Subject: RE: Balloon Demonstrations

Hello out there! I just joined the list-server today so I don't know if
anyone recently suggested this experiment. Mix a small amount of cupric
chloride ( or Lithium chloride, Barium Bromide, something colorful when
it burns) with a little methanol and put it inside a large balloon. Fill the
balloon with Hydrogen and attach it to a heavy weight using along string.
Attach a candle to a long pole and ignite the balloon. It explodes and
shows the color of the chemical inside.

John M.
Univ. of Fl, Dept. of Physics





Date: Wed, 15 Feb 1995 16:36:54 -0500
From: William Beaty
Subject: Re: Balloon Demonstrations

Take two circular sheets of mylar, one transparent and one aluminized,
seal them edge to edge, then inflate.  When under solar illumination, I
wonder if the inside mirror curve is uniform enough to light fires at its
focus.  If 100-meter mylar sheets were employed, you could go into
competition with that French research station with the giant mirror.  Or
roast REALLY BIG hotdogs on a sunny day...

William Beaty  voice:206-762-3818
EE/Programmer/Science exhibit designer        http://amasci.com/
Seattle, WA 98117                             SCIENCE HOBBYIST web page




Date: Wed, 15 Feb 1995 16:44:51 -0500
From: Richard_E_BERG@u***.edu (rb22)
Subject: Re: RE: Balloon Demonstrations

There is a great little paperback book which is probably exactly what Dave
is looking for, if one can get it quickly.

Glenn McGlathery and Larry Malone:  Tons of Scientifically Provocative and
Socially Acceptable Things to Do with Balloons under the Guise of Teaching
Science.  Copyright 1991 Libraries Unlimited, Inc.  Available from TEACHER
IDEA PRESS, A Division of Libraries Unlimited, Inc., P. O. Box 6633,
Englewood, CO 80155-6633.

Contains 83 experiments covering nine broad areas of science.  Written for
elementary and middle school students, but many of us never got beyond that
point.

Dick B.



Date: Wed, 15 Feb 1995 16:45:19 -0500
From: William Beaty
Subject: Re: Balloon Demonstrations

A friend, Jim Burrows of THE SCIENCE CLUB outreach company, uses a balloon
demo as one of the few safe explosions that kids can do.  Inflate a
balloon, tape a short length of fine steel wire to its surface, connect
this wire to the bare ends of some heavy "zip cord," speaker wire then
connect the other end of the cord to a 6V lantern battery.  The thin wire
gets red hot and bursts the balloon.  The best source of thin steel wire
is steel wool (use the grey kind, and the ultra-fine XXXX type works
well.)  To assure a good contact between the steel and the copper, wrap
the steel fiber around the copper wire then clamp it with an "alligator
clip."  I've always wanted to rig up a bunch of these with various balloon
sizes and have a computer and an interface card do the popping
automatically.  Then I can write a program to play the balloon-popping
version of THE WILLIAM TELL OVERTURE !  I'd need a couple of hundred
balloon-circuits though... 

William Beaty  voice:206-762-3818
EE/Programmer/Science exhibit designer        http://amasci.com/
Seattle, WA 98117                             SCIENCE HOBBYIST web page





Date: Wed, 15 Feb 1995 19:26:47 -0500
From: wayne@p***.us (Tony W.)
Subject: Re: Balloon Demonstrations

Blow up 4 balloons to the same size.  Rub them with a rabbit
fur.  They hover away from each other.

Take a lit match and hold it in the center of the group after
they have been charged. The balloons will come together again.
THe fire is a source of free ions that will neutralize the
charges on the balloons.

After the balloons have been charged, spray a mist of water
on the balloons.  The water vapors allow for conduction of charge
to neutralize the balloons.

Take a flip flash apart.  Cut out each flash bulb.  Hold
a balloon 10 feet away and rub it with a fur.  Hold one lead
from the flash bulb with a pair of pliers. Bring the other lead
close to the balloon. Charge will jump from the balloon to the
bulb and light it.  If the bulb doesn't light, then the bulb
charged too slowly (not enough current through it).  Just touch
the bulb to something grounded -like a sink faucet.  this
discharge will light it.

Take a 2 liter bottle, put a straw in it -a bendy straw.  Put a
balloon in it. Keep the mouth of the balloon exposed so you can
blow it up.  Inflate the balloon.  While it is inflated, remove
the straw quickly and keep the balloon over the mouth of the
bottle.  The balloon will stay inflated. (You can do similar
things with one of those (sun tea bottles.  Use the built in
valve instead of a straw.)

rest an 8 ft 2x4 on an old double convex lens.  Bring a
charged balloon close to the board and it will rotate.

Bring a charged balloon close to an empty drink can.  The can
will race to the balloon.

-tony
--




Date: Thu, 16 Feb 1995 10:02:25 -0500
From: Paul N. 
Subject: RE: Balloon Demonstrations

>Fill a balloon with helium and tie it to a weight. Put the balloon on
>a cart and then place a large bell jar around the balloon. When you
>shove the cart forward, the balloon moves forward, contrary to
>what you would expect.
>
>Ron E.

Don't forget the balloon in the car trick!

It might work with your demo bell jar if you can get enough acceleration.

Works like this:  Helium filled balloon tied to a string so that it is free to
roam around the car.  When you hit the breaks, you get pushed toward the front
of the car - the balloon gets pushed toward the rear.  Have fun watching them
explain that one.

Paul N.
Valparaiso University





Date: Thu, 16 Feb 1995 10:10:21 -0500
From: lauterburg@u***.ch (Urs L.)
Subject: Re: Balloon Demonstrations


Hello David,

As already mentioned by others I find one nice experiment making use of a
balloon to show how balloons filled with different gases
either focus or defocus sound waves. Fill the ballon with
Helium, CO2 or air. Place the balloon between a small speaker
and a microphone and measure the microphones output. I get best results
with a sine frequency of about 2.5 kHz. CO2 focuses the sound
and Helium defocuses, with air of course there is no difference.

And when you have a balloon filled with Helium, you can inhale some
of it and explain the experiment sounding like a little baby. Students
like it a lot. But probably this is an old one and therefore well known.

   greetings from Switzerland    Urs





Date: Thu, 16 Feb 1995 10:58:51 -0500
From: FNILON@P***.EDU
Subject: Re: Balloon Demonstrations

Dear fellow ballooner:
        Our astro professor likes to fill a luminous painted (spots) punch
ball with hydrogen and illuminate it with a black light:  the expanding
universe.  Then we do the big bang by igniting the balloon with a propane
torch (at arms length of course).
        You can also fill the punch ball with compressed air and do the
Newton's third law action-reaction.
        Put an tied and uninflated balloon in a vacuum chamber and pump out
the air.  Put a balloon on the end of a tube in a one hole bell jar and
pump out the air; or, stretch a rubber membrane across the bottom on the
bell jar and show how our diaphragm works.
                        2 more cents
                        Frank N.
                        Pomona College




Date: Thu, 14 Mar 1996 05:19:44 -0800 (PST)
From: William Beaty 
Subject: balloon 0-G boulder

On Fri, 8 Mar 1996 gaulf@w***.us wrote:

> Hello, I am a Lab.Tech. at Westmoreland County Community College.
> I set up the Chemistry and Physics Labs and also work with the Horticulture 
> Lab.
> This is my first message on Tap-l.
> 
> Has anyone ever tried to make a balloon from mylar ? I often see mylar 
> balloons being sold and wonder about what kind of mylar I would need and 
> where to find it.

Try a "space blanket."  This is an aluminized mylar sheet sold as an 
emergency heat-reflective blanket and usually found in camping stores 
and auto parts stores.  ("Heat" reflective???!)

One thing I did: make a 3ft. tetrahedron balloon, inflate with helium and 
seal it, then apply enough duct tape to the surface to produce neutral
buoyancy.  I took some time with the duct tape and distributed it
uniformly over the surface in small strips so that no face of the balloon
was heavier than others, and the balloon would only barely rotate to a
particular orientation. 

The end result was a strange lumpy boulder with considerable mass but zero
weight: a zero-gee object!  The mass could be felt by shaking it, or by
playing a violent game of catch.  But when released, it would just hang in
the air.  The helium only escaped slowly, and I compensated by removing
duct tape.  The large diameter of the balloon made for considerable
buoyant force, with corresponding considerable duct tape mass.  It lasted
for several days before needing more helium. 

   ____________________________________________________________

It's not too hard to make a tetrahedron balloon using mylar and rubber 
cement.  Overlap and glue opposite edges of the sheet together to form a 
tube, with about 1.5" overlap for strength, and minimal rubber cement 
for low weight.  Strong bonds are made by lightly coating opposite faces 
with rubber cement, waiting a couple minutes for partial drying, then 
laying the glued sheets together.
               
           ___----___
         /            \
       /                \
      |                  |
     |      END VIEW     ||
     |       OF TUBE     || overlap
      |                  |
       \                /
         \____    ____/
              ----


You then flatten and glue one open end together to form a long
"pillowcase"  shape, sweep the bag through the air to inflate it, then
flatten the other end closed, but on a line perpendicular to the first
sealed end.  Flatten enough of this end so that the inflated part is
tetrahedral, trim the extra back to 1.5", and overlap/glue this joint
together.  
                          ____--/\
                  ____----      ||
            __----         __--|  |
           /           __--    |  |
          /        __--       |    |
         /     __--           |    |
        / ___--                |  |
       /==____                 |  |
              ----____          ||
                      ----______\/

Yes, the points of the tetrahedron are a problem.  You can fold them over
and glue the fold to the rest of the balloon, which makes the finished
shape closer to a lumpy sphere than to a tetrahedron.  Or make 2" mylar
disks, fold them into cones (filter-paper style fold) and overlap/glue
them to the points of the balloon.  Don't forget to leave one point open
for inflation. 


Challenge: determine the dimensions needed for the sheet so that a perfect
tetrahedron will be formed when the edges are glued together. 

William Beaty  voice:206-762-3818
EE/Programmer/Science exhibit designer        http://amasci.com/
Seattle, WA 98117                             SCIENCE HOBBYIST web page





Another one: put a penny in a balloon, blow up the balloon and tie it 
off.  Now shake the balloon to get the penny bouncing, then "swirl" the 
balloon in a circular motion, and the penny will begin rolling on edge.  
The penny orbits in the balloon with the inner balloon surface acting 
like a strange "gravity well."

Once you can produce the orbiting penny effect, lay your head on a table, 
hold the balloon in one hand and get the penny to orbit, then place the 
balloon on your ear.  The sound from the penny is fabulous!  Decreasing 
frequency motor noises from all directions!  Sounds like UFOs landing.

With skill you can pull this prank: Make two penny/balloons, orbit the 
pennies VERTICALLY, so the pennies roll up over the top rather than in a 
horizontal plane.  Now, approach someone from behind, get the pennies 
going fast, and clamp the balloons on either side of the head of your 
victim.  They will experience the ufo-landing noise, but coming from all 
directions.  This gets interesting reactions.  And gives the perpetrator 
a certain reputation!

Oh, I just had a thought.  It hasn't happened to me yet, but it's 
possible that the above prank could seriously backfire if the victim was 
wearing sharp earrings, or if the balloons were inflated to nearly the 
point of rupture.  Maybe it would be better not to take someone by 
surprise with this, since one of the balloons might pop!

William Beaty  voice:206-762-3818
EE/Programmer/Science exhibit designer        http://amasci.com/
Seattle, WA 98117                             SCIENCE HOBBYIST web page



Want books? Try searching amazon.com:

(try " science experiment project" too)

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