High School Physics SMILE

Meeting 02.10.98

Notes prepared by Alex Junievicz

Comment: The next meeting is 24 February 1998 [Bridge Breaking Contest]

We will meet in the auditorium of the Hermann Union Building [HUB].

Bridge Web URL:
http://bridgecontest.phys.iit.edu/

Comment on James Coates article in Chicago Tribune: File names with a space created by some applications can be first renamed then deleted. For example, it is possible to create a file name with an internal space, which is difficult to delete. Of course, the DOS command del *.* will delete that file, as well as everything else in the [sub]directory.

James Chichester [Lincoln Way HS]

He brought in a product called Odd Balls, with ordering information

Orbix Corporation

6329 Mori Street

McLean, VA 22101

(703) 356-0695

The product is shipped as 3 balls of three different sizes, which become parts of spheres snapped together in the center by what looks like a doughnut. Each section is a different size. Unlike an orange, each slice is different.

-used to construct figures to show different colors

-used to show center of gravity of different figures

-used as an inverted pendulum (like a rocking chair) period varies with center of

mass

-parts of whole -- fractions

Designer: Dr Ben F Sherman [a retired Nuclear Engineer]

Porter’s comments: What happens when 2 cylinders intersect? They produce an intersection region that is rounded, but essentially becomes a square when looked at in a certain plane. The volume of that region may be computed as a single integral, and p does not appear in it.

V = -a ň a dx (a2-x2) = 4 a3 /3

Karlene Joseph [Lane Tech HS]

She brought in a project based on the book Why does the toast always land jelly side up?

by Robert Ehrlich.

"Make the rings by cutting 5 strips of construction paper of width several centeimeters and lengths, and lengths 15 cm, 20 cm, 25 cm, 30 cm, and 35 cm. Tape the two ends of each strip to make a circular ring and then tape each ring to a transparent base, so that the rings stand vertically next to one another in order from smallest to largest."

She constructed circular strips of paper taped on a overhead sheet, shaken on an overhead and the resonance of each was excited by shaking at a certain rate. There was a problem in that there were a number of frequencies that excited rings, and it seemed that the rings responded to a number of frequencies But harmonic caused various responses, hiding the true resonance. She used rings in increments of 5 cm. It seems that a different multiple might give better individual responses.

<--shaken-->***

*** but not stirred!

Larry Alofs [Kenwood HS]

Description of a 1973 Summer Project on resonance done with Jim Williams.

He described using a 1957 Ford blower motor to show resonance. He used a DC motor with a disk and something to cause it to be out of balance--in this case it was a screw placed on what was a squirrel cage made with only one disk left--and with a variable power source to vary the speed—i.e. the frequency of the vibration.

Now attach this to a 2"x4"x8’ board on one end and clamp the other to the table, at lower speeds the board will flex perpendicular to the wide side, and as speed is increased it will stop vibrating and as it still increased the board will vibrate in the axis of the wide side. Thus we can show the resonance of the board in each direction.

CENCO makes a speaker like device that could also cause a vibration, but his is a lot less expensive.

Comment by Porter: During the Franco-Prussian War a regiment marched across a bridge, and the bridge collapsed as they passed over it. Since then, marching soldiers always break their stride on a bridge.

Ann Brandon [Joliet West HS]

Demos of Gravity

1-with a cup with washers put on the side attached to the bottom with rubber bands, and if left in free fall the g is lost; thus the rubber pulls the washer into the cup.

2-with a cup full of water with a hole in it and dropped the water stops flowing through the hole when dropped because the water is no longer pulled out due to gravity.

Also, Ann remarked that Great America trip is NOT on the 11th because the park operators are imported from St. Louis, and they need the time to come from the other parks to operate the ILL Facility on the special days 12th and 13th.

Comments from the floor: A horse shoe magnet was attached with a metal plate just below, and far enough not to be engaged by the magnet is placed on a shelf just below the magnet. Now the system is dropped, and the magnet "without gravity" can pull up the plate with an audible "clink".

Final Reminder: The next meeting is in the HUB for the bridge contest. IIT students can submit a bridge, but it is in the College grouping. Student registration begins at 3:30, and judging is expected to start at 4PM. SMILE participants should be sure to sign the attendance sheet.