A physicist’s merry-go-round

What you can do here
  1. Stand on the edge of the still merry-go-round. Start walking along the circumference. What happens? Stop. Change your direction. What can you see?
  2. Stand on the edge of the merry-go-round. Ask someone to spin it. Note the position you have to take not to fall off the platform.
  3. When the merry-go-round is moving try to walk across it along the diameter. Is that easy?


How it works
  1. When you walk in one direction, the merry-go-round spins in the opposite direction. It happens because of the law of conservation of angular momentum which depends on the mass, size, and angular velocity of the physical system whose value is always 0 unless external force is applied to the system.
  2. To keep your balance on a rotating platform, you must lean over towards its centre. This makes all the forces acting on your body balanced, also the centrifugal force, which throws you off the platform.
  3. Walking along the diameter of a rotating merry-go-round is difficult due to the Coriolis force in the system which acts on you in the direction perpendicular to the path of movement.

Interesting facts
The Coriolis force is responsible for the direction of winds blowing in the tropics, the so-called trade winds. They were of considerable importance in the age of sail.