Re: [asa] Easy to show experiments

  Here are some nice, simple experiments for kids (or adults) which taken
together don't prove atoms, but sure point in that direction.

  1) Get a big plastic syringe (no needle) and fill it with air. Plug the
end. See how far you can compress it.
  2) Try this after filling the syringe with other gasses, such as helium
(from a balloon you purchase) or carbon dioxide (which you can get by
mixing baking soda and vinegar in a glass -- the reaction will create CO2
which, being denser than air, will drive the air out of the glass).
  3) Fill the syringe with various liquids such as water, oil, vinegar,
and prove to yourself that your really can't compress liquids the way that
you can compress gasses. (This comes as a surprise to many people, who
don't realize that molecules in a liquid are already packed close together
and touching each other).
  4) Get a styrofoam cup of liquid nitrogen (or get a hunk of dry ice);
put it in a garbage bag and seal it. Let the liquid nitrogen or dry ice
turn into a gas and measure how much the volume expands. (By taking the
cube root of the volume expansion, this even allows you to calculate how
far apart the atoms are from each other, in terms of atomic diameters, in
a room-temperature gas.)

  Now combine the above activities with the following activities:
  5) Get a large cup full of ping-pong balls and an equally large cup full
of small marbles or bee-bees. Mix them together. The final volume will
be LESS than two cups because the smaller spheres can fit in spaces
between the larger spheres.
  6) Now get two graduated cylinders. Get 50 milliliters of water and 50
milliliters of isopropyl alcohol. Pour them together. The final volume
will not be 100 ml, but about 98 ml. Same principles, but on the
molecular scale.

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  Also, with some searching on the web, you can find pictures and videos
from various research groups who have trapped single atoms (or small
numbers of atoms) in magneto-optical traps. You can literally see,
individual specks of light from laser photons scattering off individual
atoms in the trap. In other words, thanks to magneto-optical atom traps,
the old claim that "you can't see a single atom" has been false since the
early 1990's. Is that cool, or what?!

Loren Haarsma

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Received on Wed Sep 12 13:45:53 2007