061: Magnetic Cannon

–

The interesting part is when a magnetic ball collides into two stationary metallic NON-magnetic balls (@ 0:48).

Clearly, the outgoing ball had a much greater momentum and energy than the incoming ball. So is there a double violation of the conservation principles (of momentum and energy)? Gosh.

Nope. Nope.

First for momentum, notice two balls recoiled to the right after the collision. (The recoil was at quite a high speed, but friction brought them to rest quickly) So even though the outgoing ball had a large leftward momentum, after subtracting the rightward momentum of the recoil, the total momentum is still equal to the initial leftward momentum.

As for energy, note that the magnetic field must have an associated magnetic potential. Since the field is attractive, the balls must be losing magnetic potential energy as they come closer. So even though the outgoing ball had a large kinetic energy, after accounting for the loss in magnetic potential energy, the total energy is still equal to the initial total energy.

• 03 Dynamics
• 05 Work Energy Power