eli5 What causes whirlpools

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eli5 What causes whirlpools

In: Earth Science
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There are several reasons, but the most common is what is called an eddy current. Effectively, it is a place where the water moves past an area that causes it to suddenly have a change in velocity, like near the bank of a river or at the edge of a pier.

Water flowing past the point suddenly has a low-pressure point beside it, where it had a high-pressure point, and the sudden difference in pressure causes some of the water to change direction. This causes some of the surrounding water to also change direction, and some ends up pointing back into the original stream, getting pulled back into the direction change, and forming a vortex, what is commonly called a whirlpool.

Technically any time you have a fluid flowing past a stationary object, unless the object has zero cross-section, it will form eddies and “whirlpools”. This includes air, including the air you are breathing right now. Smoke rings are a controlled 3D whirlpool of air.