Announcements

• Porter Johnson called attention to the website of Richard L Garwin, who gave a very interesting talk on Nuclear Terrorism at IIT on 05 November.  Details of his work can be found at The Garwin Archive website:  http://fas.org/rlg/. The following has been excerpted from materials from the report The Technology of Megaterror, which appears at http://www.technologyreview.com/articles/garwin0902.asp, linked to that website:

  "The loss of more than 3,000 people to al-Qaeda terrorism on September 11, 2001, brought to many Americans the sudden recognition that their country was no longer leading a charmed life. But a number of the nation’s security experts had seen it coming. In 1999, for example, a commission led by Senators Gary Hart and Warren B. Rudman examined U.S. security policies and, in a report published two years before the al-Qaeda attack, concluded, “There will.... be a greater probability of [catastrophic terrorism] in the next millennium. ... Future terrorists will probably be even less hierarchically organized, and yet better networked, than they are today. Their diffuse nature will make them more anonymous, yet their ability to coordinate mass effects on a global basis will increase .... The United States should assume that it will be a target of terrorist attacks against its homeland using weapons of mass destruction. The United States will be vulnerable to such strikes.”

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 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.

Karlene Joseph [Lane Tech  HS, physics]     New Pasco Track Accessories
Karlene obtained a new Pasco [http://www.pasco.com] Collision Dynamics Track [http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=51512&Detail=1], as well as various accessories.  In particular, she showed us a Picket Fence Gate, used to obtain data with the ME-8930 Smart Timer:  http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=51477&Detail=1, which nicely and accurately determines Time, Speed, Acceleration, and other quantities as well.  Using the same projection system as used by Larry Alofs,  she proceeded to test the reproducibility of the launcher and determined the time for the cart to travel about 20 cm, at about that distance from the launch point.  The times were recorded to be 0.9093 sec, 0.8497 sec, and 0.6181 sec, as an indication that the mechanical launch system is not completely reproducible.  We also observed that it took 1.3230 sec for the cart to travel a distance of about 50 cm .She then measured the speed of the cart using the picket fence, obtaining 44.4 cm/sec and 51.2 cm/sec for the two trials.

Karlene next set up the cart on a slight incline [standard blackboard eraser placed under one end of the track], released the cart from rest, and measured the speed of the cart:  6.4 cm/sec and 6.5 cm/sec after 40 cm, and 50.2 cm/sec and 50.5 cm/sec after 80 cm.  Then she measured the acceleration of the cart directly using the Smart Timer.  She obtained 12.4 cm/sec², in rough agreement with expectations with a 1% grade. The cart was then given a push up the track from the other end -- accelerations of -22.4 cm/sec² and -24.2 cm/sec² were obtained. (Should the accelerations be the same? Why?)  This asymmetry between going left and right was an indication that the track was not level.  We did corresponding measurements on the level track, obtaining - 2.0 cm/sec² and -8.1 cm/sec², for the two cases. We concluded that some friction was present, and that the track was not perfectly level, the two effects being of comparable size.

Beautiful data and nicely phenomenological, Karlene!

"F" Lee Slick [Morgan Park HS, physics]       Mnemonics
Lee reminded us of the use of mnemonics to simplify the memorization of details that are otherwise easily forgotten.  He gave us the following examples:

Mnemosyne, the Greek goddess of memory and mother of the nine Muses can help students of nature to remember the many details of our complex world . Her namesake, mnemonics, comes from the Greek word 'mnemon' which means mindful.

Gary Guzdziol  [Carol Rosenberg Specialty School, science]        Drum Implosion Video
Gary showed us a video of the implosion of a 55 gallon drum, which was made at the SMILE summer picnic in Summer 1992. (Gary's father, Ed Guzdziol, did the experiment then.) Upon two separate occasions last semester [http://www.iit.edu/~smile/weekly/mp110403.html and http://www.iit.edu/~smile/weekly/mp111803.html], Gary heated a drum, but it did not implode, apparently because of minor leaks.  In the video the drum creaked and made noises just before the implosion, and the sounds continued after its collapse.  Why?

Gary stated that the drum was about 23 inches in diameter and 35 inches high.  Thus, the total area of the two bases is about 835 square inches, and the area of the lateral surface is about 2527 square inches, corresponding to a total area of 3358 square inches.  At a maximum pressure [inward] of 14.7 pounds per square inch, this corresponds to an total inward force of about 49,000 pounds. Wow!

Your video was dynamite, Gary! Thanks.

Monica Seelman [ST James Elementary School, science]        How much paper is there in a roll?
Monica brought a wrapped cylindrical roll of paper about 1.36 meters in height.  The roll had an inner circumference of  11.6 cm, an outer circumference of 23.6 cm, corresponding to an average circumference of 17.6 cm.  The thickness of a stack of 25 sheets was measured to be 0.6 cm, corresponding 0.024 cm per sheet. Since the paper was 2.0 cm thick on the roll, Monica felt that there were about 83 sheets in the roll.  Thus, she estimated the roll to be 14.7 meters long --- and with a height of 1.36 meters, this corresponds to an area of 20 square meters.  Larry Alofs suggested an alternative method of estimating the amount of paper, by weighing a small piece of paper of known area, and then weighing the entire roll.  This might have been more accurate, in practice.  We could have done both, and then rolled the paper out to see how long it actually was.

Thanks for showing us the way, Monica!

John Scavo [Evergreen Park HS]        Batteries Revisited
John showed us a model, remote-controlled airplane, which can be recharged in a few minutes with a docking port.  The Radio Controlled Air Hog Resistor is described as follows on the Amazon.com website:

"With a remote control that is simple to master, this two-speed airplane is perfect as a first radio-controlled toy. The Resistor takes off from its own computer-operated launch pad with a single press of the Launch button from the remote. A large toggle button moves the plane either left or right as the plane hits scale speeds of up to 400 mph and flies up to 300 feet away. For quick speed, a Thrust button on the remote gives it a 25-percent extra power boost, and for a smooth, even landing, a Land button brings the Resistor down safely. Except for a few hard plastic components that house the engine, this lightweight plane is made almost entirely of Styrofoam, which damages easily if it hits obstacles so it's best to practice flying in open, treeless areas. This toy requires six C batteries for the charger and one 9-volt battery for the plane itself and requires only a three-minute charge in the docking station before it's ready to fly."

John also showed us a remote control car [heavily battered through use!], which he had obtained for about $5. Thanks for letting us play with your toys, John!

We ran out of time before all the presentations were completed.  These presentations will  be scheduled first at our next meeting, 18 November 2003:

• Don Kanner: Paul G Hewitt
• Fred Farnell
• Ann Brandon: Pressure Revisited