Why does the water tilt to one side when being spun on a rotating platform?

Question

Its the phenomenon we always see that when you place a cup of water on the edge a rotating platform and spin it, the water level in the cup will tilt to one side.
What causes the water to tilt?
And why does the normal force acts perpendicular to the water surface?

Please provide concrete answers, ambiguous answers don't really help..

This question has been bogging my friends and my teachers could not really give me a satisfactory answer.

Thanks!

How does the centrifugal cause the water to tilt?

This ficitious force is equal and opposite to the centripetal force. If so, isn't the centripetal force a resultant force already? Why is a centrifugal force present?

And why does the normal contact force shift as the water level is tilted? How does it shift? Why does it always stay perpendicular to the water surface?

This question is a bit different from a bucket of water being spun vertically. Now its being spun horizontally.

And of course, the water doesn't evaporate.

If possible, how does one calculate the angle of tilt of the water surface?

Answer 1

the answer is simple, and john q provided it.

it has nothing to do with gravity.

it will eventually evaporate. unless there is a lid on the cup

Answer 2

Good question. It is the same reaction you get when a bucket of water is suspended from a rope and spun - as soon as the water picks up speed, the water will sink in the middle and climb up the sides of the bucket.

Any object that has motion tends to travel in the straightest path, any other path is the result of other forces and results in an acceleration. In other words, an object in orbit - even if its velocity is constant - is being accelerated toward the object it is orbiting. If the force causing this acceleration was not present, the object would simply ride off into space. In this case, the "force" acting on it is gravity.

And most physicists think that the phenomenon of your glass of water experiment is the result of gravitational forces throughout the universe. The accelerated water "wants" to travel straight, but the "force" of the side of the glass prevents this - and, in a futile effort to travel straight, the water is displaced against the glass and tilts toward the side.

Answer 3

Centrifugal force---if the cup happened to be in the exact center of the rotating platform, the water would hit all places on the sides evenly.

Answer 4

Centrifugal stress inward, well-known stress outward. In a beaker, centrifugal stress is the stress exerted via the wall of the beaker that keeps the water from leaving the beaker (i.e, water would not penetrate glass). although, centrifugal stress is the different of the 'well-known stress' which reasons the water to desire to flee, and for that reason 'tilt'. action = reaction. Centrifugal = well-known stress.

Answer 5

Really?

Usually the water evaporates right?