PURPOSE: To demonstrate conservation of momentum in elastic collisions.

DESCRIPTION: Air track gliders on a frictionless track are used to illustrate inelastic 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 glider. 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.

Use pairs of masses which have opposite sex of velcro for inelastic collisions. The mass with the tab is pushed through the first gate to commence the collision.

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, with opposite sex velcro, one of each having the 5 cm timing tab.

SETUP TIME: 5 min.

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