Demonstrates the relationship between simple harmonic motion and uniform motion round a circle.

Unit consists of black metal disc, approximately 200 mm dia, supported on clear plastic base white marker 13 mm dia may be rotated just inside periphery of disc by means of handle at tear of disc. Similar marker moves along a slot across a diameter of the disc, always in phase with the peripheral marker, performing simple harmonic motion when the handle turned at uniform speed. May be used with the slot horizontal or vertical.