"I wanted to remind you of the high school modeling workshop this summer, sponsored by ISU and the Illinois Board of Higher Education and held at Dominican University in River Forest 7/11-29/2005. This is a great program that will transform your teaching--it really changed how I thought about curriculum and content--and participating teachers will receive $2400 plus a bunch of equipment. More details are here http://cmsi.cps.k12.il.us/ViewNewsDetails.aspx?pid=1797&id=267.. It'd be great if there was a strong CPS presence at this, so please let me know if you need help with applications or your school to make this happen."
Ann Brandon [Joliet West HS,
Workshop on Standing Wave Machine
Ann held a workshop in which 8 participants constructed the standing wave machine, which she showed us at the last SMILE meeting, mp041205.html. Good job, everybody! Special thanks to Ann.
Fred Schaal [Lane Tech HS,
Follow-up Questions on Book by Michio Kaku
As a follow-up of his comments about this book at the last SMILE meeting mp041205.html, Fred asked two important questions concerning developments in twentieth century physics. Here are his questions, as well as the answers, given on-the-spot by Porter Johnson.
Babatunde Taiwo [Dunbar
Simple Electric Motors
Babatunde showed an electric motor that he had built according to the instructions obtained from Pasco Scientific Teacher Resource Guide [Investigation Seven: Making a Model Motor from Scratch, pp T-285,286], using a D-cell battery, about 1.5 meters of magnetic wire, a battery holder, masking tape, a strong magnet, and a two paper clips. The following explanation is excerpted from that source:
"Stored chemical in the cell established an electric pressure difference which pushed charge through the coil -- but only if the coil is oriented so that scraped ends are in contact with the clips. (If the insulated half of one end is in contact with the clips, no charge can flow.) Using the Right Hand Rule for Motors (7.11), once can predict the direction of the force on the wire on the two sides of the coil, and therefore which way the coil will rotate."His students were able to construct a simple electric motor, complete with field magnet, rotor, and commutator, in one class period by following these instructions. For details on a very similar procedure, see the lesson given by Lee Slick in SMILE on 11 November 1997 [ph1111.htm], and those given by Ann Brandon in SMILE on 23 March 2004 [mp032304.html].
Earl Zwicker informed us that descriptions of both of these experiments have appeared in The Physics Teacher TPT:
Average Rolling Time
|05 cm||2.25 sec|
|10 cm||2.36 sec|
|15 cm||2.18 sec|
|18 cm||2.18 sec|
So far, so trivial! Fred assumed that the marble was perfectly round, and that it rolled without slipping down the inclined plane. Under these conditions, the component of acceleration down the plane, which is inclined at angle q above the horizontal, is
An related question posed by Porter Johnson:
Q: What happens when a tire is rolled without slipping at an oblique angle down an inclined plane?"A excellent experiment to challenge physics understanding. Thanks, Fred!
Don Kanner and Bill Blunk [Joliet West HS,
You Can't Win at Tug-of-War just by Pulling Harder
Don and Bill stood facing each other, each holding one end of his own spring scales. The other ends of the scales were then hooked together between them. They pulled in opposite directions, Don attempting to get and maintain a scale reading of 50 Newtons (about 12 pounds) and Bill tried to maintain 100 Newtons (about 24 pounds). Don merely chased Bill across the room with increasing speed -- or did Bill pull Don! They always had about the same scale reading, despite their efforts. It may have been an exercise in frustration for them, but it was quite entertaining for us. Why did they fail? Isaac Newton and his laws of motion have something to say about this. Don't they?
It was an excellent Katzenjammer Kinderen comedy routine, which served to illustrate the consequences of Newton's Laws.
By chance, are you twins? Thanks, Don and Bill.
Bill Shanks [Joliet Central, physics --
Meeting of the Board + A One
Bill recently was driving North on Interstate 75 in Georgia, on a quiet section between Macon and the metropolitan Atlanta traffic snarl. Suddenly, he saw a large wooden board moving through the air in front of him, coming right at him. Fortunately, he was able to swerve to avoid major impact, receiving only a minor dent on the right front bumper. After this moment of terror had passed, Bill began to wonder whether he had just been lucky, or whether there had been time to react to the situation. Aha! Another good physics question! The board might have been lying on the road initially, where it would be struck by a big truck and knocked high into the air. If it rose to an approximate height h = 3 meters above the roof of the car before Bill saw it and it began to descend, a time t ~ 0.8 seconds would elapse before it came down to the level of the roof:
Excellent real-life physics experience! Thanks, Bill.
Comment by Porter Johnson: By contrast, an object dropped from a viaduct above the road is even more dangerous, since you probably won't see it until somewhat after it is dropped, and at that point it is moving more quickly through the field of view.
Bill showed his newest flashlight acquisition -- a one-watt LED diode white light flashlight that he had obtained at Sam's Club Joliet (about $13). After we darkened the room, Bill turned on the light, which seemed to be quite bright. He removed its lens and reflector to expose the bare LED, practically a point source. We looked at the light through the "slits" formed by our fingers, and were able to see diffraction patterns, with the red, green, and blue colors separated!
Nifty gadget! Thanks, Bill
See you at our final meeting of the year, 10 May 2005.
Notes prepared by Porter Johnson