Question

When a toilet is flushed or a sink is drained, the water (and other material) begins to rotate about the drain on the way down. Assuming no initial rotation and a flow initially directly straight toward the drain, explain what causes the rotation and which direction it has in the northern hemisphere. (Note that this is a small effect and in most toilets the rotation is caused by directional water jets.) Would the direction of rotation reverse if water were forced up the drain?

a) Coriolis effect causes rotation; clockwise in the northern hemisphere.
b) Centrifugal force causes rotation; counterclockwise in the northern hemisphere.
c) Angular momentum conservation causes rotation; direction depends on the water flow.
d) No rotation occurs; rotation direction depends on water flow.

Answer 1

The Coriolis effect causes a minor counterclockwise rotation when water drains in the Northern Hemisphere, but household water rotation is usually due to the design of plumbing fixtures.

Step-by-step explanation:

When a toilet is flushed or a sink is drained without any initial rotation, the Coriolis effect can cause the water to begin rotating as it goes down the drain in the Northern Hemisphere. This effect, although very small in such a situation, would cause the rotation to be counterclockwise in the Northern Hemisphere.

However, in most household scenarios, the rotation is dictated more by the design of the toilet or sink, such as the placement and direction of water jets, rather than the Coriolis effect. If water were forced up a drain, the Coriolis effect would still apply, but whether this would reverse the direction of rotation would depend on the specific setup and forces involved. For example, forcing water up a symmetrical drain without directional jets would likely result in a clockwise rotation in the Northern Hemisphere due to the Coriolis effect.