Stone Ball

How can this stone ball of spectrolite granite be so easy to spin, even though it is so heavy? The ball has a diameter of 60 cm and weighs 360 kg.

In the centre of the bowl in which the ball is resting there is a nozzle that emits a stream of water. The pressure of the stream is magnified across the complete surface and can in this way lift the heavy ball on a water membrane. This makes it easy to spin.