Bernoulli's principle within a fluid

Bernoulli's Prinicple, Archimedes Principle (buoyancy), centrifugal force.

Bernoulli's Top, overhead projector

The density of the balls is smaller than water's, so the balls naturally float in water. When spin the top, the water at the outer edge moves faster than water in the centre, thus pressure is lower at the edge and higher in centre. When top first spins, the balls tend to move outwards due to the pressure difference. But after a very short while, the balls get dragged by the water in the top, and spins with the water. In the rotational frame the water and the balls are stationary with respect to each other, and the Bernoulli's effect no longer exist on the balls. So the balls move towards the centre due to centrifugal force.

the balls are now stuck in the top; however, you can still see the same effect with the air bubbles

Updated: 02/23/16