What it shows:

An object finds itself heavier and pinned against the wall of a spinning cylinder; the principle behind fairground Barrel of Fun rides and centrifuges.

How it works:

The object in such a ride experiences two forces, that of its weight and the centripetal force exerted by the barrel wall; the vector addition of these forces giving the apparent increase in weight (figure 1 ) The reaction force of the object also presses it against the wall; the increased friction force preventing it from sliding down.

The barrel in our demo is a 45cm diameter, 30cm high clear Plexiglas cylinder mounted on a turntable. The victim here is nothing more than a cube of rubber sponge (6×3×3cm) or a tightly wound ball of wool (a hamster would be ideal, but we're nice guys). With a coefficient of friction of 0.62, a minimum rotation speed of 1.3 rps will hold up a damp sponge on the wall. To ensure that the object stays high on the wall, it needs to be introduced already moving. Throw (almost like a roulette ball delivery) the sponge with your hand matching the rotation speed of the barrel.