when you slowly rotate the mug/jar/glass/etc, why does the water (or other drink) in it not rotate with it?

Question

when you slowly rotate the mug/jar/glass/etc, why does the water (or other drink) in it not rotate with it?

In: 15

Answer 1

Objects at rest want to stay at rest, this includes liquids.

However, in the case of a rotating glass with liquid inside, the liquid near the side of the glass will rotate with the glass when it starts. The longer you rotate it for, the liquid near the middle of the glass will start rotating, until eventually all the liquid is rotating at the same speed as the glass.