SMILE HS Physics 03-10-98

Prepared by Alex Junievicz

Note: Summer SMILE activities will not be supported by Eisenhower funds this year, but instead teachers and staff will be paid directly by the Chicago Public Schools. The program will operate in a different framework, lasting 3 hours per day [1:15 - 4:15 pm] for 4 weeks [06-31 July] and providing 2semester hours of academic credit. The classes will meet in the afternoons, so that CPS teachers can teach in summer school in the morning. There will be two sections of 15 teachers and five staff members each; one section will emphasize Physics and Mathematics, whereas the other will emphasize Biology and Chemistry. Teachers from grades K - 12 will be permitted to enroll in the courses, with preference be given to regular classroom teachers who have not previously been in the SMILE summer program. To get your name on the summer list, or to get an application for our database for a friend, please call Porter Johnson [312] 567-5745.

Larry Alofs [Kenwood Academy]

Re-designing a Boyle's Law experiment without Mercury. Instead he is using ethylene glycol (antifreeze), along with a tire pump and a pressure/vacuum gauge. Thereby, he can achieve much higher pressures than would be possible with a Mercury column of modest height.

Height of trapped air Gauge Pressure Total Pressure P 4 V
5.6 cm 50 lb/in2 65 lb/in2 364 rel units
6.5 " 40 " " 55 " " 358 " "
8.1 " 29 " " 44 " " 356 " "
10.2 " 20 " " 35 " " 357 " "
14.2 " 10 " " 25 " " 355 " "
23.9 " 0 " " 15 " " 359 " "

One must add atmospheric pressure to the gauge pressure to determine the total pressure P in the gas. Note that P ´ V is roughly constant as the gas volume is changed.

Another configuration with a thermal/ice water bath may be used to show Charles Law.

Earl Zwicker explained that a tire pump has a leather cup shaped seal , which is pushed up on the "up" stroke, and then on the "down" stroke it expands to provide a seal for the piston.

Porter Johnson: The most dangerous advice he ever received at a service station was that a low tire will "pump itself up" as you drive down the road, so that there is no need to pump up the tire. Actually, as the tire gets warm the pressure inside will increase, and an under-inflated tire will get dangerously warm because it is less rigid and there is more rolling friction. Heat, in turn, is the primary cause of tire failure.

Editor’s Note -- Many gas stations have gone to the coin-operated compressors over a tank style—in part because people filling bicycle tires can be injured if the tire explodes when it is pumped to a ridiculously high pressure with a "tank" compressor.

Bill Blunk [Joliet Central HS]

Electrostatics - a way of calculating electrostatic forces in the spirit of charging "pith balls", using balloons charged with fur, which repel one other. Then measure the distance of separation at equilibrium and the mass of each balloon. With d = .8 meters and masses of 2.5 g (.0025 Kg) , we get about 1.3 ´ 10-6 Coulombs.

Roy Coleman commented that two one Coulomb charges separated by one meter repel at 1010 Newtons --to give a feel for the effect of a one Coulomb charge.

[Another comment was that students are quick to state that a solution is impossible because of missing facts, whereas the missing data is not necessary when it cancels out in the process of doing the math.]

Hoi Huynh [Clemente HS]

She used graph paper to illustrate the Pythagorean Theorem, and showed a demonstration of it using the areas of the regions on the graph paper. She extended the resulting angle figure, rotated the figure, and applied ways of resolving the differences.

In the diagram, the area of the big square is (a + b)2, whereas the area of each of the four triangles of sides a and b is ½ ab. The area of the inner square is c2 , and

(a + b)2 = c2 + 4 ´ ½ab ; or a2 + b2 = c2.

Comment by Porter Johnson: The Pythagoreans were an ancient Greek cult who explored the mystical wonders of mathematics, and who were forbidden to reveal their mathematical discoveries upon punishment by death.