Basic Idea:

• Check for conservation of momentum during elastic and inelastic collisions. Note: we have new air tracks; these instructions are for the old ones!

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What:	How Many:	Where:
Air Tracks	1	151 Lab (Bewkes 204 – under the bench with computers)
Air Carts	1 – Large, and 2 – Small (w/matching Velcro)	Majors Storeroom, shelf B3
Foot pads	3	Majors Storeroom, shelf B4
Photogates	2	non-Majors Storeroom, BB3
Rubber bands (to secure photogates to track)	2	Physics office
Vernier calipers	All we have	non-Majors storeroom, shelf BB3
Shared stuff
Small bubble level	1 or 2	Ask Jeff

Computers Needed?

• Yes.

• Lab Setup:

  

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• Air track setup (connect to the overhead air supply with a hose clamp):
  

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• Leveling of air tracks:
  

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• Attaching photogates to airtrack (the base of the photgate sits on top of the I-beam; use rubber bands to hold it in place):

  

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• Set photogates to gate, 1 ms, and memory On (the red light is on).

• Aircarts should have small metal angle bracket taped on top flush with one end to trip the photogate. Make sure photogates are tripped by this "flag", and not the cart (there is a small hole in the cart that can cause erroneous readings).

• On sunny days, the window shades should be drawn; bright sunlight will affect photgate performance.

• Be sure the air tracks are as clean as possible - use acetone if necessary. Also, check the under surface of the air carts for dents and scratchs; use a small file to smooth.

• The bubble level is used to check the level of the track.

• Make sure that students indicate the track they used; some are better than others.

• The speed of a collision can create problems. Elastic collisions produce better results with slower speeds; inelastic works better with faster speeds. Also, when both carts are of the same speed (for an elastic collision), small numbers produce huge errors!