For example, we have a bottle filled with water to the point when there’s no space left in that bottle, is the water still moving as we shake the bottle?

Question

For example, we have a bottle filled with water to the point when there’s no space left in that bottle, is the water still moving as we shake the bottle?

In: Physics

Answer 1

Here’s a thought experiment we can do to illustrate why the water would move within the bottle.

Imagine you have a pot of water filled halfway up, and you spin the pot around. As the metal pot rotates, you’ll see that the water inside it basically doesn’t move, and the reason for this is intuitive. The circular pot doesn’t really have any way to move the water just by rotating, other than friction, and the water has lot of inertia. The water wants to stay put, it doesn’t care whether the container around it moves.

Now imagine that instead of a circular pot, you have a (for whatever reason) oblong, oval shaped pot. You do the same experiment. Is the water going to move as the container rotates around it? It has to, because effectively the shape of its container is changing and the shape of the water has to change to accommodate that. But it still has inertia and doesn’t want to move, so it wouldn’t just all rotate with the container. It would be a much more chaotic (turbulent) movement.

Now extend this idea to a water bottle. Filled or not, as the position of the container changes, the position of the water has to change with it. If you rotate the water bottle sideways (not along its axis), you have an extension of the oval pot scenario. The water has the container pushing it one way and it’s inertia opposing that motion, so you get all kinds of movement within the water.