PURPOSE: To demonstrate conservation of energy and conservation of momentum in elastic collisions.

DESCRIPTION: Air track gliders on a frictionless track are used to illustrate elastic collisions. A photocell gate timer is used to measure the time taken by a 5 cm tab on the glider to pass through the photocell gate and thus to obtain the velocity of the gliders. To obtain more than one timer reading the gates must be positioned carefully and the timer reset between readings using the cable-mounted reset switch.

SUGGESTIONS: Practice may be necessary.

REFERENCES: (PIRA 1N30.30) See also "Instructions for Air Track Photocell Gate Timer" in Demonstration Reference File.

EQUIPMENT: Air track, gates with timer, gliders with tabs: two each mass M, 2M, and 3M.

SETUP TIME: 5 min.

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