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PURPOSE: To demonstrate the inertial property of mass.
DESCRIPTION: Load the arms with equal masses at the same or different distances from the center, and observe what happens when the cart is accelerated by hand along the track. Alternatively, load the arms with masses in the ratio of 10:1 which look the same and ask students to account for the behavior of the apparatus. By lifting one end of the track, show that when a force (gravity) is allowed to act uniformly on all parts of the apparatus the crossarm will not rotate regardless of how it is loaded.
A simple demonstration sequence is to place more mass on one side (at front in pictures above) and accelerate the cart with your hand to illustrate inertial mass (at left), then let the cart accelerate down the inclined track to illustrate gravitational mass (at right).
SUGGESTIONS: Level the track.
See Question of the Week #115, Question of the Week #116, and Question of the Week #117 for information on using this demonstration to enhance class involvement.
REFERENCES: Available. (PIRA 1F10.10)
EQUIPMENT: Cart, track, equal mass pair, unequal mass pair, as photographed.
SETUP TIME: 10 min.
