High School Mathematics-Physics SMILE Meeting
1997-2006 Academic Years
Waves

25 November 1997: Bill Blunk [Joliet Central HS]
A Simple demo of wave beats using pop bottles.

Having the bottles filled more than half and blowing over the tops produces a tone, the frequency of which can be changed by adding or subtracting some of the H2O in the bottles. One person can excite the two bottles, but it is much more practical for two people, each with one bottle.

Comments were made that an echo at a time of about 40milliseconds [ms] later is acceptable, whereas echoes at time delays of 200 ms are aesthetically detrimental. A live room with a short echo is appreciated while echoes over time intervals greater than 100 ms cause the sounds to seem dissonant to the listener. Also, piano tuners use harmonic resonance to tune a piano in the higher octaves, [ http://hyperphysics.phy-astr.gsu.edu/hbase/music/pianof.html#c1] and they can resolve differences of 1/5 cps using beats.

01 May 2001 Fred Farnell (Lane Tech HS, Physics)  What happens when waves meet?
put some paper cups on the floor and stretched a slinky™ across the floor, which was held at its ends by two assistants.  An assistant, by rapidly moving his end of the spring back and forth once {transverse to the direction of the stretched string), sends a transverse wave pulse toward the other end. When the other end was held fixed, the wave was seen to reverse its orientation and direction after reflection at the fixed end.  The cups were put parallel to the stretched slinky on both sides of it, and the goal was to set up waves that would knock down all of the cups.  This was seen to be difficult, if not impossible.  Then, the assistants set up waves coming in simultaneously from each end, so that we could see the slinky before, during, and after the overlapping intersection of the wave pulses in the middle.  Very interesting, Fred!

22 April 2003: Ann Brandon [Joliet West HS, Physics]      Waves and Resonance
Ann led us through three exercises to illustrate wave properties:

 Ann, you struck a resonance with our thoughts! Very nice!

Don Kanner [Lane Tech HS,  Physics]           A Quick Connection 
Don  was inspired to think about Physics when he saw a girl with a pony tail hairdo running into the wind and away from him.  The girl's ponytail moved in a circular pattern on the left side, and then swished to the right side to move in a circular pattern there.  Why didn't rotate up and down, instead? Don felt that the eddies in the wind produced this "resonant oscillation", similarly to those in the collapse of the Tacoma Narrows Bridge in November 1940 (see the SMILE writeup for 25 February 2003:).  Don felt that "somebody" should obtain a DVD recorder and make digital images to illustrate various principles and concepts of physics.  Is this practical?

Thanks, Don.

12 April 2005: Ann Brandon [Joliet West HS, physics]              Making Waves
Ann
showed us her home-made device for showing modes of vibration of a string.  The device contains a dry cell battery pack, two DC motors, a potentiometer, string, and two plastic rods attached to a wooden base.  The motors are anchored to the plastic rods and attached to drive opposite ends of the string..  Transverse vibrations of the string are induced, with the tension in the string varied by stretching it. For details and a photo see the notes from the Math-Physics SMILE meeting of 22 April 2003. As the tension in the string is increased, the velocity v of transverse vibrations also increases.  The frequency f of transverse vibrations is determined by the (fixed) rotational frequency of the motors.  Because of the relation v = l f, the wavelength l increases in this case. We thus get fewer nodes on the string when we increase the tension. We produced stable oscillations with 1, 2, 3, and 4 internal nodes on the string.

Ann will bring materials for us to construct several of the devices at our next meeting,.  Great physics show! Thanks, Ann.

26 April 2005: Ann Brandon [Joliet West HS, physics]              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.  Good job, everybody! Special thanks to Ann.