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Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538

Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography

PLEASE REQUEST DEMOS WELL IN ADVANCE

Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.

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 Thermal Properties Of Matter
 Thermometer Collection
 Liquid Crystal
 Absolute Zero
  video  - Thermal Expansion
 LN2 - Thermal Effects on Solids and Gases
 Heat And The First Law
 Change Of State
 Kinetic Theory
 Gas Law
 Entropy And The Second Law

 video  - Thermal Expansion

Purpose:

To demonstrate expansion due to thermal changes.

Procedure:

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  DEMO VIDEO DOWNLOAD w/ sound / 1920x1080 / 24.19Mb/s / 633MB size  

  DEMO VIDEO DOWNLOAD w/ sound / 854x480 / 5.69Mb/s / 157MB size  


  1. BALL & RING: Ball does not fit thru Ring at room temp, but upon heating the ring w/ Bunsen burner, the ball does (use wide head Bunsen burner centered under ring placed on stand, heat for 30 seconds, do not place hot ring onto lecture bench to avoid burning surface).
  2. BI-METALLIC STRIP: The red tape indicates steel side, white indicates brass side. With the steel side facing up and exposed to a bunsen burner flame, the strip bends up due to higher thermal expansion of brass. The opposite effect results when exposing the strip to LN2. Fractional expansion per degree Celcius: Brass = 19 x 10-6/oC and Steel = 13 x 10-6/oC
  3. BOLT CRACKER: A bolt or cast iron bar may be broken in the cracker. Make sure bolt fits in hole loosely, then the clamp must be fairly tight before beginning the demonstration. To be able to "crack" the cast iron bolts more than once, align the bolt in the cracker such that once it cracks, there is a piece of bolt long enough to be used for another demo. (ie. Allow one end to stick out the side less than 1 cm so that after the bolt breaks, there is enough bolt length left on the other "half" to use for a second time)
  4. EXPANSION APPARATUS: Shows the expansion of different metal tubes by heating with a steam generator.

Hints:

  • For the cracker, fit the bolt "off-center" into the hole so that it projects no more than 1 cm on one side of the bar. If one does not do this (ie. one centers the bolt), the bolt will not be usable for a second time. The idea is to have one piece of the bolt be long enough to be used again another time.
  • One can carry out the demo in "reverse" order, cooling the bar. In this case, place bolt in an "outside" hole. Heat up bar, as it expands, keep tightening clamp to maintain tension in bar/bolt system. When bar no longer expands, tighten clamp again and shut off torch. As bar cools, it will contract and eventually break the bolt. Advantage to this way is "cooling" process is quiet and allows one to "hear" the bolt snap. The propane torch tends to be a bit noisy. Ref: Tyndall's Breaker Bar.

Equipment:

  • Bi-metallic strip
  • Bolt cracker
  • Bunsen burner
  • Expansion apparatus with steam generator
  • Propane Torch
  • Ring and Ball