NYU Physics Demos

Seismic Accelerator

Topics: Mechanics - Energy Transfer

Equipment: Seismic accelerator kit with goggles and instruction manual.

Setup: Four balls should be set up on a plastic rod as shown. The blue ball is attached rigidly to the rod, while the rest of the balls are removable. The small red ball is the only one that bounces off of the rod, and as such there are spares. Simply arrange the balls on the rod as shown, hold the rod by the exposed end such that the other end is hanging downward, and drop the rod and balls straight to the floor, ideally a smooth and level surface.

The small red ball will launch off the rod, flying vertically many times higher than the distance from which it was dropped. We know from conservation of energy that an object will not bounce above its point of origin, because some energy was lost to air resistance and when the ball made contact with the ground. In this case, we consider the energy of all four balls. If dropped separately, they would lose their potential energy, gain kinetic energy during the fall, and then transfer that energy into the ground as thermal energy, and also to potential energy yet again such that it can bounce back up. But when the balls are stacked, the potential energy gained after hitting the ground is transferred to the ball above it, so the energy from the three bottom balls is transferred to the top ball, which is enough to launch it violently upwards.

Location: Shelf

Notes: Use caution when bouncing the balls, and wear safety goggles. Also, watch wear the red ball rolls, to avoid losing it.

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