A coin is put on a phonograph turntable. The motor is started but, before the final speed of rotation is reached,the coin files off. Explain why.

When the phonograph turntable starts rotating, the centrifuge acts on the coin placed on it. Because of the friction between the surface of the turntable and the coin, there will be a centripetal force to balance the centrifugal.As long as the balance exists between the two forces, the coin will stay on the turntable. But with increase in the rotation speed of the turntable, the magnitude of centrifugal force on the coin increases against the centripetal force provided by friction. Eventually, the coin would fly off the surface of the turntable before the table reaches its maximum speed