High School Physics SMILE
07 April 1998
Notes taken by Alex Junievicz/Porter Johnson
Announcements by Porter Johnson [IIT]
1. There will be another web exploring session this semester:
Saturday, 02 May 1998
9:00 - 11:30 am
Life Sciences Building Room 206
[3101 South Dearborn]
All teachers and students are invited to attend.
You can read about it on the web page
[or, you can click over from the SMILE home page: http://www.iit.edu/~smile/]
Announcement by Jane Shields [Chicago Academy]
The lesson on Bernoulliís Principle given last time was taken from the book
Science and the Bible by Donald B Deyoung 
[Baker Books; P O Box 400; Grand Rapids MI 49516]
Comment by Porter Johnson: check out Amazon.com [on-line book vendor]
Bill Lilly [Kenwood High School; Math Dept]
He demonstrated the capabilities of the CBR [Calculator-Based Ranger], which is a sonic motion detector that provides information in digital and easily convertible form. The device is made by Texas Instruments for use with their calculators TI-82, 83, 85, 86, or 92. The price is $90, and seems to be dropping with time. The "innards" of the device are the same as a Polaroid auto-focus system. The apparatus was demonstrated by hanging a bottle on a swing and swinging it back and forth as a pendulum. He was able to obtain [interpolated] numerical values of x, v, and a at time intervals of about 0.1 seconds, so that motions could be studied quantitatively, and graphs easily generated.
Richard Goberville [Joliet Central High School]
He showed very small balancing birds, which are available at about 12 per dollar from the following source:
4206 S 108th Street
Omaha NE 68137-1215
In addition, he showed a "Centripetal Force Puller" which consists of two masses attached by a string, with a collar around the string for "twirling" the lighter mass about a horizontal plane. The light mass is about 20 grams, whereas the heavier one at the base is about 120 grams.
The light mass was rotated in a circle of about one meter, with the time for 10 complete revolutions being 6.1 seconds. Thus the period of revolution is T = 0.61 seconds. Using the formula T = 2 p /w , we determine the angular velocity to be 10.3 radians/second.
The net [centripetal] force on the 20 gram mass is
F = m w 2 r = 1.1 Newtons.
This force of 1.1 Newtons balances the 120 gram weight hanging at the bottom, so that the numbers are consistent.
Fred Schaal [Lane Tech High School]
Fred discussed why ice cream doesnít get really hard in "frost free" freezers. The process of refrigeration inevitably generates "frost", and the frost-free freezers have an automatic defrost cycle every 8-12 hours. A fan blows against the cooling coils during the cooling cycles, and during the defrost cycle the transfers the moisture to a condensing region outside the frost chamber. Simple, yet elegant, non? Frost-free refrigerators are far less energy-efficient than their simpler counterparts, since there are heaters as well as coolers present, and the defrost cycle is intrinsically wasteful. Still, they are very convenient in practice.
Estelvania Sanders [Chicago Vocational High School]
She had an interactive lesson on using the caloric, sugar, fat, NaCl [salt], and cholesterol content of milk, pop, shakes, and various "Dagwood style" do-it-yourself sandwiches to evaluate foods, by combining weighted combinations of the contents of the various ingredients. Estelvania did this demonstration with full signing, using signs for the ingredients, including "pop". This lesson was very interesting, but it made us all very hungry to be dealing with food just before quitting time.