Foucault's Pendulum and Inertial Oscillation

Finding the center of rotation

If the supporting point of the pendulum is not positioned at the center of rotation, the pendulum resonates with the rotation of the table and the pendulum weight is thrown out by centrifugal force. Thus we have to ensure the center of rotation and the support point of the pendulum coincide, however finding the center of rotation at a point midair above the rotating table is more difficult than it seems.

In this experiment, we pointed a laser beam at the temporarily secured support point of the pendulum from a stationary point outside the rotating system, and repeatedly adjusted the support point until it stayed still relative to the laser beam through 180 degrees.

Erasing the pendulum's support point

If you place a camera directly above the support point of the pendulum, the beam holding the pendulum sits right in front of the camera. In order to make the beam stand out less, we opened the aperture to maximum, set the focal point away from the beam and adjusted the exposure using an ND filter.

Making a special light globe

A normal globe was too bright for our purposes, and we didn't have a suitable ND filter on hand, so we made a special light globe using an LED and a resistor, and used that instead. That's the reason the locus is red.

 

Pressing the camera on the rotating stable's shutter

Normal electronic remote controls can't be used for long exposure (bulb) photography. You have to physically press the shutter button, so we pressed the button by using an electromagnetic solenoid (an apparatus that moves in a piston motion using magnets) and controled from outside the rotating system .