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?

Water is a colorless, transparent, odorless liquid that makes up the oceans, lakes, rivers, and rain, as well as the fluids that keep living beings alive.

When a toilet or sink is flushed or drained, the toilet or sink becomes an inertial frame of reference. An imaginary force acts in this frame of reference, carrying water or another substance away from the center of rotation, causing it to rotate down the path.

The direction of rotation in the Northern hemisphere is counter-clockwise as the direction of the earth in the Northern hemisphere is counterclockwise. Yes, the direction of rotation would be reversed if water were forced up the drain because the earth rotates clockwise as viewed from the southern hemisphere.