when you slowly rotate the mug/jar/glass/etc, why does the water (or other drink) in it not rotate with it?
In: 15
It does…kinda.
Imagine the glass as a big ball pit and the water like the balls. Since the water is a liquid, the balls aren’t glued together. If you put the ball-pit glass on a merry-go-round and spin it suddenly SUPER fast (consider how fast the side of the glass must look to the teeny tiny water molecules), the balls on the edge will move because they were touching the sides—they’re pushed by friction—but not as fast as the wall because some of that motion goes instead to rolling or jostling in a different direction (or is lost to heat). The next layer in of balls will start to move too, but only because the outermost layer pushes them, and this layer will move a little slower for the same reason—they’re not glued to the other balls so they mostly get pushed forward but also then bounce off sideways or roll away or what have you. So some more of the motion is lost.
By the time you get to the balls in the very middle, they might not move at all, or move very little.
If you keep spinning the ball pit, though, eventually enough of the motion will make it all the way through these individual ball-molecules that they all start to move. This will happen in a regular-sized glass too if you spin it long enough.
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