A very large arch is found at the top of every pinball game. After the ball leaves the shooter and travels up the lane and onto the playfield, it always rolls back and forth along the edge of this arch before dropping away to the main playfield area. Although not very important to the game play, it nonetheless has some physics behind it. On some games there may be other arch areas that will redirect the pinball to other areas of the playfield.

The physics:

When the ball enters the arch, the arch applies a normal force on the ball which causes the ball to constantly change direction and exhibit circular motion. The normal force of the arch on the ball along with the gravitational force provide the centripetal force to produce the circular motion.

The ball may bound back and forth along the arch several times. As the ball slows the magnitude of the normal force changes since less velocity requires less centripetal force. The size of the gravitational force does not change so the force supplied by the arch continues to decrease.

As the ball slows (a result of friction and a series of inelastic collisions with the stops on the left and right) eventually the velocity is so low that gravity is more than enough to pull the ball out of the circular path and take a parabolic path down onto the main playfield.