Coriolis Force

What it shows:

The Coriolis force is a pseudo force existing in a frame that rotates with constant angular velocity to a reference frame. It acts on a body moving in the rotating frame to deflect its motion sideways. Here the audience sits in the reference frame, while two volunteers on a rotating platform experience the coriolis force by trying to basket a volleyball.

How it works:

The two volunteer's task is to throw a volleyball into a wastebasket mounted mid-way between them at the center of rotation. The audience view events from an inertial frame; it sees the ball thrown from the left (figure 1) with velocity v towards the basket, but they also see a tangential velocity due to the rotation of the platform. The resultant of these velocities makes the ball swerve to the right, missing the basket. The thrower of the ball sees the situation from a non-inertial frame. Although they project the ball straight towards the basket, it veers off to the right - the mysterious coriolis force ending the dream of playing for the Celtics. Coriolis acceleration is given by

ac = 2ωv

The rotating platform consists of a 3.2m length plank, cross dimensions 30cm × 5cm (12" × 2"), mounted on a rotating platform. 1 Seat backs are attached to each end for the comfort of the participants (and to stop them falling back off the ends).

figure 1. The coriolis force turntable

coriolis force

Setting it up:

This demo needs a lot of space to do its thing, so it will probably need to take priority over other demos.

coriolis force


An effect that has a significant influence on the weather patterns of the Earth. Here the rotation of the planet and the movement of air currents into a low pressure region combine to force the winds into circular paths.

1 Cenco 74790 turntable