14 September 1999

Notes taken by Earl Zwicker

Carol Zimmerman [Lane Tech HS]
set up a piston/cylinder arrangement made of glass, like a syringe. The piston (rubber) trapped air inside, and air volume V could be measured directly (in cc) on the glass cylinder. Weights (known masses) were added to the piston to compress the air to a smaller volume, and keeping a record of weight and corresponding volume, one could use the equation for pressure: p = mg/a, and test the relation between p and V. Since g and a (piston area) are fixed, and m is added mass (observed), p is directly proportional to m. From Boyle's law, pV = const, a plot of m vs V should show a hyperbolic relation. When we collected data, it did! Carol said that in the classroom, plots of p vs 1/V resulted in a convincing straight line. Nice!

Walter McDonald [CPS Sub; Great Lakes Vet Ctr]
showed us a small apparatus with a wire coil and variable capacitor, and a 5.7 V 60 Hz power supply. He passed out copies of a lab experiment: The Q Meter and Measuring Inductance. Then he described some results he obtained. The series R-L-C circuit was to be tuned to resonance and voltage measured across the C.

Ann Brandon [Joliet West HS]
showed us a "ping pong ball cannon." A plastic water bottle (used by bicylers) has an opening which accepts a ping pong ball with slight friction. Two nails had been poked through opposite sides of the bottle, near its bottom, to provide a spark gap within the bottle. Ann added a small amount of methanol, placed the ping pong ball into the bottle's mouth, and connected a piezoelectric spark generator (such as used to ignite propane stoves) to the nail electrode. When she triggered the spark generator - POW - the ball flew out across the room! (Not enough force to hurt anyone however.) Can you think of physics and chemistry concepts that are illustrated with this? Neat!

Carl Martikean [Wallace School, IN]
read us an amusing story in which guiding principles of physics/chemistry are used to lead to answers to the question: Is Hell Exothermic or Endothermic? Fun and interesting!

Bill Blunk [Joliet Central HS]
showed us a pair of old tank (as in WW II) periscopes, and then held them sideways up to his eyes, so that he would see things as if his eyes were as far apart (about 0.5 m) as the objectives of the periscopes. He then asked us how this might affect the way we interpret what we see. After a few guesses, we were invited up to try the experiment for ourselves. Bill stood about ten feet in front of the observer, then extended his arm out toward the observer. Wow! It appeared as if his arm was very long, coming impossibly closer to the observer. Quite an effect!

Bill Colson [Morgan Park HS]
placed a disk on a phonograph turntable; the disk was a black-on-white drawing of an inward spiral (actually three spirals). As it rotated it gave the impression of a whirlpool spiraling inward. Bill told us to concentrate our gaze at its center for a while, then to look at one of two pictures he had on display. When we did this, the images in the pictures appeared to move. One was the "expanding universe," and the other of "clouds." Quite a sensory illusion! Of course, this leads to questions about what goes on in our vision and brain to lead to such effects? Any ideas? Bill passed out a 1981 paper, "The Jerry Andrus Tri-Zonal Space Warper", which described what he showed us, and more.