Announcement

Al Tobecksen [Richards HS],
a long-term SMILE participant and mentor, was recently killed in an automobile accident. We will always remember Al for his light-hearted and dedicated approach to teaching. His wife Therese Tobecksen [ST Anthony School, Calumet City], also a long-term SMILE participant, has asked that I put this poem in our write-up:

Achievement
-adapted from Robert Lewis Stevenson

Successful teachers are those who have lived well, laughed often, and loved much;
who have gained the respect of their colleagues and the love of children;
who leave the world better than they found it---whether by a hovercraft, water balloon launcher, or other science "toys";
who never lacked appreciation of earth's wonder or failed to express it;
who looked for the best in others and gave the best they had!

She said that she would never have seen Al "wearing his teacher hat" if she hadn't seen him in SMILE. We'll miss you every day, Al!

Mathematics-Physics High School SMILE Meeting
26 September 2000
Notes Prepared by Earl Zwicker

          OUR NEXT MEETING...
                ...will be October 10, 2000
          4:15 p.m.
          111 LS

Porter Johnson (IIT Physics), Roy Coleman, and Ed Scanlon (Morgan Park HS)  met with the SMART group for a few minutes in another location, so they could focus on their mission.  In particular, they discussed the Policy on Student Acceptable Use of the Chicago Public Schools Network, as described in the code of conduct available at http://www.cps.edu/Documents/Resources/StudentCodeOfConduct/Section2_StudentCodeofConduct.pdf

Fred Schaal (Lane Tech HS)
presented "92s to the Rescue." He gave one hand-held TI 92 to Betty Roombos (Lane Tech HS) to enter commands and data. The LCD display of the TI 92 was projected onto the screen for all to see. Fred placed on the board: a/sinA = ? - referring to the Law of Sines. He instructed Betty how to draw a triangle and label its vertices with angles A,B,C, and the sides opposite with a,b,c. Betty was a whiz, and with Fred's further direction she soon had the angle A labeled with its value of 41.99o, and the side a = 2.28 cm, taken as a "measured" value. The ratio R = a/sinA was calculated as 3.41 cm. Then, as Betty dragged the top vertex, C, around the screen of the TI 92 (as one does with a mouse on a PC), the triangle changed its linear and angular dimensions, and the changing value of R was seen to range from 3.10 to 4.77 and higher. When the sizes of angles were measured to be in radians instead of degrees, the range of values of R continued to be the same. Beautiful! What a great way for students to develop an intuition for the Law of Sines and what it tells us about the geometry of plane triangles. Thanks, Fred, for phenomenological math!

Walter McDonald (sub - CPS)
set up before us a torsion balance, and gave us a handout (Microsoft Encarta Encyclopedia) describing its uses. Walter told us he had found Joel Hofslund's (Kenwood HS) mini-teach on the SMILE website, and decided to see if he could detect the gravitational force of attraction. A thin rod with masses at each end was suspended from its center by a fine wire about 40 cm long. The rod was free to rotate in a horizontal plane about the wire as a vertical axis. If it rotated, the wire would twist, setting up a torque. When Walter moved another pair of masses near those at the ends of the rod, the rod rotated AWAY from those masses, indicating repulsive force rather than an attractive one caused by gravitational forces! This stimulated discussion, with some of us pointing out that electrical forces between like charges would produce repulsion, and that is probably what we were seeing. Others pointed out that electrical forces are very much stronger than gravitational forces. Earl Zwicker (IIT physics) placed information from a physics text on the board, showing that two 1 kg masses one meter apart would attract each other with a gravitational force of 6.7x10-7 N or 1.5x10-7 lb! Very small indeed! Walter succeeded in refreshing our thinking on this problem; thanks, Walter!

Marilynn Stone (Lane Tech HS)
made an inclined plane by placing a book on the table and leaning a grooved plastic (about 1 ft) ruler against it - using tape to fasten its lower end to the table. She placed a steel ball (a little over 1 cm diameter) in the groove at the top end of the ruler and released it. It rolled down the groove, onto the table, traveled horizontally across the table, rolled off the edge, and fell to the floor. Marilynn took the horizontal distance from the bottom of the ruler to the edge of the table to be 0.5 m. By measuring the time it took the ball to roll off the edge of the table (0.54 s) we could calculate the horizontal speed:

 vx = d/t = (0.5 m)/(0.54 s) = 0.93 m/s.

The height (y) of the table was measured to be 0.92 m, and y = gt2/2. So putting in values for y and g = 9.8 m/s2, we found the time of fall to be t = 0.43 s. When the ball fell off the table and was accelerated downward by gravity, it continued to move with the same horizontal speed as it fell, so it moved a distance

x = vxt = (0.93 m/s)(0.43 s) = 0.4 m 

from the edge of the table by the time it hit the floor. Marilynn placed a cup at that position, released the ball as before, and sure enough! - the ball fell into the cup! (Though it did bounce right out, due to elastic forces!) Just to convince us, she did it again.

"Students are always surprised to see that it actually works, as predicted by the physics," 

Marilynn told us. Great!

Fred Farnell (Lane Tech HS)
walked carefully across the front of the room in front of us and asked,

"What would a graph of this motion look like?"

Using the same projection setup as Fred Schaal, Fred F. connected a sonic ranger (CBR) to a TI 83, and to the projector. He explained that a high frequency sound wave was sent out by the CBR, which would then be reflected from Fred's body back to the CBR where the reflected wave would be detected. Next, he walked carefully, as before, away from the CBR which put data about Fred's position (D) and speed (v) at various times (t) into the TI 83. He then caused the D vs t data to be displayed on the screen, and data points appeared to lie roughly in a straight line with positive slope. Using
y = mx + b

and a program in the TI 83, he found the best-fit values of m and b to the data and plotted it. It seemed like it was not a very good fit to us.

Next, Fred repeated the experiment, but this time ran away from the CBR. The D vs t graph of his motion appeared parabolic, typical of constant acceleration motion. When he found the best fit to the parabolic equation,

y = ax2 + bx + c,

and plotted it on the same graph as the experimental points, the result did not look like a best fit to many of us. He also tried fitting to an exponential equation, with the same kind of result. This leaves something for us to explain, but Fred certainly showed us what wonderful things can be done experimentally right in the classroom these days. Good phenomenological physics, Fred!

Bill Colson (Morgan Park HS)
gave us handouts containing an explanation for why dry air is heavier (more dense) than moist air, from Tom Skilling's weather page (website http://wgntv.trb.com/news/weather/) in the Chicago Tribune (http://chicagotribune.com . He wondered about any relevance of Avogadro's number to this. Ideas? [Comment by PJ:  Avogadro's number tells you how many molecules of an ideal gas there are in one mole of the gas, corresponding to a volume  of 22.4 liters at STP. The higher the molecular weight of gas, the heavier one mole will be, and thus the denser the gas. Water vapor [molecular weight 18] thus replaces nitrogen [molecular weight 28] and oxygen [molecular weight 32] molecules, to produce less dense air.  Thus, home runs in baseball are more likely on humid days!   

Ann Brandon (Joliet West HS)
blew on a Stadium Horn she had bought at K-Mart, and pointed out salient features of its construction. Then she showed us how one could make the same thing from an old film can and some PVC pipe. She blew on a version of that, and sure enough! - Ann showed us "sound" physics!

Larry Alofs (Kenwood HS)
held up a transparent plastic gadget called Mysterious Magnet Tube, from Science Kit ; telephone number 1 (800) 828-7777; website http://www.sciencekit.com (cat.no.46213, $12.95). Imagine a cylinder about 9-10 cm in diameter and 10 cm long with its open ends sealed off. Then place a smaller diameter (say 1.5 cm) cylinder coaxially with it, which pierces through the sealed ends of the larger one. In the space between the two are some iron filings. When Larry placed a cow magnet into the smaller cylinder which then could travel within the larger one, the iron filings lined up to trace out the shape of the 3-D magnetic field surrounding the cow magnet! Neat! We recalled the "poor man's" version made by Harry Hasegawa (ret- Lawndale Comm.Acad.) from a transparent soda bottle, a plastic tube, iron filings and some epoxy putty to seal it. Larry passed it around for us to play with. Thanks, Larry!

The good ideas keep coming!
DON'T MISS THE NEXT ONE!
SEE YOU THERE!!