3A40.20 - Simple Harmonic Motion as the Linear Projection of Circular Motion
Synchronize the simple harmonic motion of a pendulum with the projection of a turntable's motion.
First, a short rod is stuck to the top of a turntable and shadow-graphed with a filament bulb housed in a shield onto the side wall. Now a pendulum is hung directly above the center of the turntable and its length is adjusted so that its period is the same as that of the turntable. The speed is about 33 rpms and the pendulum is going to be approximately 70cm long. If the pendulum is now swung in phase with the pointer on the turntable with an amplitude equal to the radius of the pointer, the shadow graph will show the two moving as if one.
Start the turntable rotation. Referencing the shadow graph, when the rod lines up with the position of the pulled back pendulum, release it and watch the two items swing/rotate in phase. It is important to practice as releasing the pendulum at the wrong time will confuse the viewer.