Why does water does not fall when a bucket is rotated . . .

Question : Why does water does not fall when a bucket is rotated in a vertical circle?

Doubt by Raghav

Solution : 

As we know, to move any body in a circular path, we need centripetal force. When a bucket with water is rotated in a vertical circle, the required centripetal force is provided by the weight of the water and the bucket. So, the weight of the water, which could cause it to fall, is already used in providing the necessary centripetal force. This is why the water in the bucket does not fall when it is rotated in a vertical circle.

Here, we need to understand that when the speed of the rotating bucket is slowed down, the centripetal force decreases (F = mv²/r), and it is no longer able to counteract the force of gravity.

Further Explanation

At the top of the circle, gravity is pulling the water downward. For the water to stay in the bucket, the centripetal force (caused by the bucket’s speed) must be strong enough to keep the water pressed against the bottom of the bucket. If the speed is too low, the centripetal force becomes weaker than gravity, and gravity causes the water to fall.

Note : Here we could also use the concept of inertia to explain the above phenomenon.