If a circular vessel of water spins, how is the water in the vessel affected?

Question

Thanks! What is the relationship between the speed at which the vessel spins, as opposed to the water inside? If the vessel spin was relatively slow, would the water perhaps not spin at all?

Answer 1

Yes, friction between the vessel and adjacent water molecules will begin to accelerate them. In turn, they will begin to accelerate their neighbors. Once a water molecule starts moving, by Newton's first law of motion, it will tend to continue in motion at the same speed and direction, unless acted upon by other forces. Like, hitting the walls of the vessel. So, friction accelerates the water parallel to the walls of the vessel. Contact with the vessel accelerated the water toward the center, causing it to assume a circular 'orbit'.

In equilibrium, all the water spins at the same angular velocity as the vessel. The faster the spin, the less water will be at the center.

There is no such thing as 'centrifugal force'.

Answer 2

Viscous forces will cause the water to start spinning too. Then, the centrifugal force pushing the water towards the outer walls will cause the surface of the water to take on a parabolic shape.

This technique is used to preset the shape of large glass mirrors for telescopes. Spin up molten glass, then cool it down slowly so it solidifies with the parabolic surface.

Edit: The water will always spin with the vessel, no matter how slow you spin it. For the water to sit still, you would need a zero viscosity with no friction between the water and vessel.

Answer 3

The centrifugal forces and centripetal forces will act on the water.

This causes the water to form a trough at the center and rise towards the rim of the vessel. If the force of rotation increases the water will spill out of the vessel.

Answer 4

Coriolis effect.