NYU Physics Demos

Conservation of Momentum

Topics: Mechanics - Momentum, Newton’s Third Law

Equipment: Pendulum mounted to wooden base, on wheels.

Setup: Place the cart down a smooth surface. Mark the locations of the front and rear ends of the cart. Without letting the cart move, lift the pendulum to one side and release it.

As the pendulum swings, the cart will move back and forth, opposite the direction of the pendulum. When the pendulum is finished swinging, the cart should be back in its place of origin, which was marked earlier.

This is conservation of momentum. As the ball swings, it accelerates, and exerts a force on the cart, to which it is mounted, in the opposite direction (Newton’s Third Law). Then, as the ball swings the other way, it once again accelerates and exerts a force on the cart, pushing it the other way. Once the pendulum stops swinging, there is no displacement of mass- the ball is back where it was originally. Therefore, the cart must also be back where it was before the ball started swinging.

Location: Shelf B-f4

Notes:

Keywords: Newton, Energy, Oscillate, Roll, Conserve


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