Mechanics > Relative Motion DCS# 1E20.10
FOUCAULT PENDULUM
 Foucault pendulum
APPARATUS
iron frame next to 101-13
iron pendulum bob next to 101-13
steel pendulum wire next to 101-13
big electromagnet on plexiglas stand in wooden box next to 101-13
circuit box with variac and rectifier next to 101-13
1.5 A ammeter 101-02-D6
340 ohm variable resistor 101-02-D6
degree scale 101-02-D6
variac 202-08-H
 
DESCRIPTION
The rotation of the plane of a free-swinging pendulum shows that the surface of the rotating eath is not fixed in an inertial reference frame.  Due to Coriolis forces, at Oberlin's latitude of 41.3° N the plane of the swing precesses 9.9° per hour.

The electromagnet under the pendulum bob is switched on twice each cycle (when the steel pendulum wire contacts the charron ring) to replace the energy lost to friction.

 
NOTES

This is intended for the display case, but can be set up elsewhere.

Level frame with leveling screws.   Adjust wire length and electromagnet height so bob is just above magnet.  Set variac to 40 V and adjust variable resistor so that amplitude of swing remains constant.
wiring diagram for foucault pendulum
This Foucault pendulum was built by John Michener, OC'83, as a winter term project in 1980.

 
REFERENCES

Wallace A. Hilton, "The Foucault Pendulum: A Corridor Demonstration," Am. J. Phys. vol 46, 436-440, (1978).