Each ball orbits in its own plane, at right angles to the wave direction, and each ball is 12 degrees out of phase with the preceding one. When viewed at right angles to the wave motion, this rotating helix of balls becomes a familiar sine wave and cosine wave. The waves are shown as shadows cast on the floor and back wall.

The pale purple disk and the green disk are 180 degrees out of phase with each other (they’re at opposite sides of their orbits). This animation helps you to understand the relationship between circular motion and sine waves.