Barrel of Fun
centripetal force - circular motion - effective weight
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 turntabletot. 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 rotation speed of (Ÿ rotation speed?),
the sponge or wool will be held up on the wall at the point of application. 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.
figure 1. the Barrel of Fun forces
Setting it up:
The Plexi cylinder needs to be taped centrally (use the grid lines) to the turntable platform.
Comments:
The rate of separation of materials of different densities is proportional to g. An ultracenrifuges
can reach accelerations of several hundred thousand g, dramatically increasing effective weights
and so decreasing separation times. Rating **