High School Mathematics-Physics SMILE Meeting 1997-2006 Academic Years Miscellaneous Materials

07 April 1998  Fred Schaal [Lane Tech High School]
Fred discussed why ice cream doesn't 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.

16 March 1999: F. J. Schaal [Lane Tech HS]
He was working with the Boy Scouts, and they had a egg and a bottle. They had the egg sucked into the bottle, and he was exploring ways of getting the egg out of the bottle, next week he as going to show us the bottle (if he could get the bottle from the Boy Scouts).  04 May 1999: More on the egg and the bottle. He was thinking of way to get the egg out of the bottle that is was sucked into. Starting a fire so as to build pressure to push the egg out?? If the pressure is too great the bottle will explode??? Jet-x rocket fuel...maybe the model rocked fuel that was around a while back could be lit and push the egg out.

Someone commented that just blowing into the bottle might give enough pressure to force the egg out?

16 March 1999: Don Kanner [Lane Tech HS]
He brought back something that was done in the 70's. He hung a dry cleaner bag that was turned into a ribbon by nothing and twisting. He also had a FIRE EXTINGUISHER ready and a bucket of water to catch the drippings of the burning plastic rope. As it burned the drippings turned blue (better combustion) and made a sound as it fell. The pitch as estimated to be around 6-800 cps and as it fell the pitch increased. Another facet was that there seemed to be a strobe of the burning flame as it fell. The blue flame also seemed to be oscillating??? Why?? Doppler was not an issue since the falling flame was perpendicular to us??? It seems that a dry cleaner bag works best

14 September 1999: Carl Martikean [Wallace School, IN]
read us an amusing story in which guiding principles of physics/chemistry are used to lead to answers to the question: Is Hell Exothermic or Endothermic? Fun and interesting!  See the website http://www.pinetree.net/humor/thermodynamics.html.

09 November 1999:  Ann Brandon (Joliet West HS)
held up a liquid crystal thermometer in the form of a thin aluminum plate shaped like a very broad, inverted U, (about 12 cm long x 8 cm wide, with 2 cm "legs") with strips of liquid crystal film mounted on its top surface. Ann pointed out the patch of color on the strips of film, indicating room temperature. Two shallow dishes were placed on the table, and cold water was placed in one, hot water in the other. Ann put the thermometer down so that one aluminum "leg" rested in the hot water and the other in cold water. As we gathered around, we could see the temperature-indicating color patches on the strips moving until they formed a straight, diagonal line connecting the hot end to the cold end. What a beautiful, graphic, convincing way to show linear temperature drop from heat source to heat sink for uniform thermal conductivity through the aluminum! (A Giveaway from an ISPP meeting at DePaul!) Thanks, Ann!

22 January 2002: Bill Shanks (Joliet Central, retired) Solar Heating/Cooling (a favorite subject of Leo Seren's)
Bill and others mentioned various matters.

• He suggested using a water reservoir [2 meters in diameter, of weight about 30 tons] to store heat energy in the home, to make it warmer in the winter and cooler in the summer. These reservoirs, and even smaller ones, are common in the state of California, where a state income tax credit for passive solar heating and cooling systems existed for years. Roy Coleman said that one friend in California had built an above-ground swimming pool for this purpose.
• Another plan involved plastic sheeting and piping around a house, with either pumps or gravity feed.
• A further suggestion involved cold air intakes for fireplaces and furnaces, as well as dampers that automatically close when not needed.  The cold air intake is a major component in reducing infiltration of Radon Gas from the ground.
• Solar heating and cooling by blowing air over rocks put underneath a house.
• Buckminster Fuller's Dymaxion House in Dearborn Michigan [http://www.hfmgv.org/dymaxion/].
  "The Dymaxion's round shape minimized heat loss and the amount of materials needed, while bestowing the strength to successfully fend off a 1964 tornado that missed by only a few hundred yards. And the Dymaxion only weighs about 3000 pounds versus the 150 tons of an average home!"  Source:  http://www.thirteen.org/bucky/house.html. See also http://en.wikipedia.org/wiki/Dymaxion_house.  There was some discussion as to whether damage in the tornado is caused primarily by the wind itself, or by the debris that is carried in the tornado.  Both are obviously important.  The first effect was illustrated some time ago in SMILE by Bill Blunk by driving a pencil though a sheet of plywood with a CO₂ fire extinguisher.

08 October 2002: Bill Blunk [Joliet Central, Physics]     Molecular Shish Kabob
Bill showed us the Matter Model Kit [ME-9825; $64.00; to see an image click here], which he obtained from the 2002 Pasco Physics and Data Collection Catalog [http://www.pasco.com], which contains the following information:

• Dynamic Model of Solid Materials
• Excellent Visualization of Wave Motion
• Easily Assembled into a Variety of Configurations

Includes:
• 40 atoms
• 60 heavy springs (high spring constant)
• 60 light springs (low spring constant)
• 30 nuts (for increasing the atom mass)
• 1 brass rod (for longitudinal waves)

Typical Applications:
• Normal Forces -- Students can better understand normal forces when heavy objects are placed on the Matter Model and they can see the deflection of the atoms in response.
• Modeling a Solid -- By constructing a matrix of spheres, students can build a model of matter that is dynamic and responds to external forces similarly to real solids.
• Wave Properties -- Students can investigate wave properties including reflection, wave speed and standing waves.
• Atmospheric Pressure -- By placing the atoms on the included brass rod and holding it vertically, students can better understand why atmospheric pressure and altitude are inversely related.

04 November 2003: Larry Alofs [Kenwood HS,  Physics]        Why measure resistance?
Larry set up the mini-camera system obtained recently from All Electronics Corporation [http://allelectronics.com/].  He hooked it directly into the projection system built into the classroom, and it worked perfectly. He focused it on the screen of a digital Volt-Ohm-Meter [VOM], which he set to measure resistance.  With all of us now able to see its readings, Larry  then went through several exercises to show why it is important to be able to measure resistance, as well as how to measure it.

• Light Bulbs.  He measured the resistance of a 40 Watt light bulb (cold), and obtained 27-30 W [Ohms].  By contrast, when the bulb is in full operation with a 120 Volt source, the calculated resistance would be R= V²/P = 360 W. Its resistance should increase with temperature by an order of magnitude during the process of heating.  For comparison, he measured the (cold) resistance of a 60 Watt bulb to be 17 W. The steady state value with a 120 Volt source should be  R = V²/P = 240 W, corresponding to a power of 60 Watts.
• Jeep tail light bulb.  We could easily see (using the camera) that there were two filaments in the bulb, corresponding to (cold) resistances of 2 W and 0.7W, respectively.  The thicker filament, with lesser resistance, is used for the (brighter) turn signal or brake light, whereas the thinner filament, with greater resistance, is used for the (less bright) tail light.  Once again, these resistances are significantly less than those for full operation, but their measurement does serve as a test of whether the filaments have been burned out.  In practice, it is crucial to know whether a tail light bulb is bad, or whether there is a defect in the circuitry.
• Jeep Temperature Sensor. This device contains a thermistor made of semi-conducting material, for which the resistance decreases with increasing temperature. It is used to measure the temperature of the engine coolant, and it is connected to the onboard computer to permit adjustment of the fuel mixture.  The following numbers were given in the service manual for the vehicle:

  Temperature	Resistance
  100 °C	185 W
  20 °C	3400 W
  -40 °C	100 kW

  Larry measured the resistance with his meter to be 2300 W, which seemed reasonable, since the room was warm. Then he held a match under the sensor, and we observed its resistance to decrease to around 1700 W, with the temperature estimated to be around 40 °C. The sensor device seemed to be working properly. Does anybody wish to purchase a spare? For more details on engine coolant temperature sensors see Tech to Tech:  http://www.asashop.org/autoinc/may98/techtotech.htm and Coolant Temperature Sensor Circuit: http://www.autoshop101.com/forms/h32.pdf#search=%22Coolant%20Temperature%20Sensor%20Circuit%22.
• Throttle Position Sensor.  This device contains two potentiometers driven by the same shaft, which monitors the throttle position and sends the information to the  engine onboard computer, as well as to the transmission. Larry showed that the resistance changed continuously from 2300 W to 4300 W, except that there were "jumpy" readings at the high end. This variability causes the onboard computer to recognize this as a failure, and to go into a "safe mode" of operation.  For additional information see Throttle Position Sensors: http://en.wikipedia.org/wiki/Throttle_position_sensor  and  Tech Tips: Throttle Position Sensor:  http://www.fierofocus.com/articles/tt-throttlepossensor.html.

20 April 2004: Monica Seelman [ST James Elementary School]         Bubble Trumpets and Bubble Recipes
Monica pulled out a Bubble Trumpet, which she had obtained from Tangent Toy Company: http://www.tangenttoy.com/trumpet.html. (3 page handout)  She had learned about this device from the article Playthings of Science by Fred Guterl, which appeared in the December 1996 issue of Discover Magazine: http://www.discover.com/issues/dec-96/. When she dipped this device into the bubble solution, and then held it up and blew hard on the mouthpiece, a froth filled with bubbles was produced.  By contrast, when she repeated the procedure and blew slowly but steadily, a single large bubble came out of the trumpet.  She then asked the following questions:

• Why do individual free bubbles form a sphere?  The reason is that the sphere is the surface of minimum area for a given volume.  The bubbles contain a certain amount of trapped air, and form the spherical shape to minimize the surface free energy, and therefore the surface area.
• Why do bubble intersections occur at an angle of 120°?  Again, to minimize the surface free energy.
• When we watch a bubble, we may see many colors in its surface.  Why?  Certain wavelengths (colors) of reflected light interfere destructively, and thus the total reflected intensity is weak.

Thanks for delving into the mysteries of bubble science, Monica!

09 November 2004: Bill Shanks [New Lenox Environs,  at large]           Water Source Detector?
Bill brought in a device with prongs that required batteries, which can be inserted into a soft medium or fluid It looked like a very large black plastic fork, with two metal-pointed tines.  The device has the labels Well, Medium Well, Medium, Medium Rare, Rare, and Very Rare.  It is not used to determine the source of water, but to give some indication as to the temperature.  The device, a Thermal Fork, was obtained at Walgreens for about $10.  How does it work?  The following answers were given:

For additional information see New Types of Food Thermometers:  http://www.amazon.com/Taylor-1482-Digital-Fork-Thermometer/dp/B00009WE44.  A Very interesting question, Bill!

10 May 2005: Larry Alofs  [Kenwood HS, physics]               Stirling Engine
Larry show us the AJS 66415 Stirling engine model https://www1.fishersci.com/Coupon?cid=1341&gid=2368582&details=Y, which he had obtained from Fischer Scientific: https://www1.fishersci.com/. The following description is given:

"Heat from a small candle sends this Stirling engine model into oscillation almost immediately. Easy to construct, this unit demonstrates the Stirling engine principle. A test tube acts as the cylinder and four marbles work as a transfer piston."

For additional information on Stirling engines, see the American Stirling Company website:  http://www.stirlingengine.com/

Physics at work!  Thanks, Larry.

29 November 2005: Fred Schaal (Lane Tech)               Conserving the Heat of my toes
Fred recently broke his leg and has had a cast. How should Fred keep his toes warm with just the little "boot" that is provided to put over his stockinged foot?. He put a stocking cap over his toes, with a plastic bag over the cap, the entire "apparatus" being held in place with a bungee cord. Very enterprising, Fred!

24 January 2006: Roy Coleman (Morgan Park HS, retired!)              Color changes
Ann Brandon is a "cover girl" on the 75th anniversary issue of the The Physics Teacher! Roy has been judging science fairs the past week, and ran across a problem with zeroes, specifically a girl who stated that there are currently 750 people in the world who speak English. A couple of weeks ago a student asked why wetting a cloth with water darkens the shade of the color! For a partial answer see the website:  How does water change the apparent 'darkness' of many objects? by MIT physics graduate student Jason Goodman: http://groups.csail.mit.edu/graphics/pubs/wet_materials_egwr99.pdf. This is a deceptively simple question, one for us to think about and discuss in later meetings!  Thanks, Roy!

21 March 2006: Bill Colson commented on the Mr Calm - Mr Angry optical illusion at the last meeting. Bill had gone to one of the web sites included in the newsletter. Bill said that the writer of one of the web sites explained that each image is overprinted with features at different resolutions, presumably features appearing and disappearing as you get closer to or farther away from the image.