This apparatus is designed to demonstrate the concept and working principle of pure simple harmonic motion. As the crank rotates, it drives the bar in oscillating manner. Same mechanism is observed in piston and crankshaft motion in engine.
In this apparatus disc is mounted on bearing having holder on its surface and it is joined with a bar through holder. Disc has a rotational scale and its angle is checked at any position. Scale is placed with solid bar and bar displacement can be determined at any disc angle.