Water in a rotating sphere

What you can do here
Look at the surface of the liquid when the container is still. Gradually increase the angular velocity of the sphere. What happens inside the sphere?
Examine what the world around you looks like when you look at it through a thin the layer of liquid in a whirling sphere.


How it works
In a quickly rotating sphere the fluid moves outside and upwards. This is due to centrifugal force which appears in a rotating frame of reference. The magnitude of centrifugal force depends on the angular velocity of the container – the higher the rotation speed, the bigger the centrifugal force, and the further away from the centre of the sphere the liquid is pushed. At the highest velocity, the water gathers around the sphere’s equator. Stopping the sphere suddenly or slowing it down makes the fluid go down.
The liquid layer in the sphere acts also as a lens. When you look through the lifted fluid, the image you see is inverted.


Interesting facts
You can dry laundry by whirling it. You can skim milk by whirling it. Processing uranium in fast-whirling centrifuges enriches this element of power the generation or military purposes.