Foucault pendulum

A foucault pendulum consists of a heavy bob suspended by a very long wire (~12m or longer). The plane of oscillation of the pendulum is seen to rotate relative to the ground. This is explained as due to Coriolis force acting on the swinging bob. Because Coriolis force arises because of earth rotation, the rotation of the oscillation plane provides a proof on the rotation of the earth.

The angular speed of the rotation of the swinging plane of the bob is given by,
w = 360.sin(L) degrees per day
where L is the latitude on which the pedulum swings.

Thus, the swinging plane doesn't rotate at the equation (latitude L = 0 degree). On the pole (L = 90 degrees), the plane rotates 360 degrees in one day.

Should a Foucault pendulum be set up in Hong Kong (latitude 22.3 degrees), the swinging plane would rotate 360.sin(22.3) = 137 degrees in 24 hour. That is, the swinging plane makes one complete rotation in 63 hours (= 2 days and 15 hours).