Why water creates a whirlpool when going down the drain?

Question

Why water creates a whirlpool when going down the drain?

In: Physics

Answer 1

Conservation of angular momentum. If there’s any rotation in the water at all (which there almost certainly will be, unless you’ve left it to stand for hours) then that rotation will concentrate and get faster as the water shrinks toward the plughole, causing the whirlpool effect.