Purpose: Demonstrate inertial forces in bodies submerged in air and in water.
Description: On one side of the arm a ping-pong ball is suspended by a string from the top of a jar filled with air. On the opposite side of the arm a ping-pong ball is attached by a string to the bottom of a jar filled with water. When the arm is rotated, the ball in the air jar moves outward and the ball in the water jar moves inward.
