The following little experiment was prompted by a mention of Newton's bucket experiment, in which a bucket is filled half-full with water, suspended from a rope, and the rope and bucket are twisted. Letting the bucket go, it spins, and gradually the water within the bucket comes up to speed, and its level rises on the sides of the bucket. When the rope unwinds and the bucket stops spinning, the water continues to rotate for a while, and its surface continues to be concave. (Ref - John Moffat, "Reinventing Gravity", 2008, pp 36-37)

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A bucket with vertical sides, containing 3 litres of water, was placed on a record turntable. The radius of the bucket was 10.2 cm.

Photo #1 was taken at start, when the bucket and water were still. The water came to just under the 3.0 litre mark on the bucket.

The record turntable was switched on to its 45 rpm speed. The turntable quickly came up to speed - and that speed was 45 rpm (ie, the 3 kg mass of the bucket and water did not cause the turntable's motor to run slower than its rated speed).

The water started rotating, as could be seen by observing dust specks in the water. Specks further from the central axis had a higher angular speed, and within a minute were rotating at almost 45 rpm. Specks nearer the central axis took longer to come up to angular speed. Eventually, after about 5-7 minutes, all the water was rotating at or near 45 rpm.

Photo #2 was taken when the bucket and water were rotating at 45 rpm. The water level came to about the 3.1 litre level on the side of the bucket.

The turntable was switched off, and the rotation of the bucket was stopped. The water continued to rotate.

Photo #3 was taken when the bucket had been stopped but the water was still rotating, slowing down from 45 rpm. The water level was still above the 3.0 litre mark on the bucket, but below the 3.1 litre level.

After several minutes, the water had slowed down, and its level had dropped.

Photo #4 was taken when the bucket and the water had both stopped. The water level had returned to just above the 3.0 litre mark on the bucket.

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