A whirlpool is a large, swirling body of water produced by ocean tides. In popular imagination, but only rarely in reality, they can have the dangerous effect of destroying boats.

The vast majority of whirlpools are not very powerful. More powerful ones are more properly termed maelstroms. Vortex is the proper term for any whirlpool that has a downdraft. (Technically, these approximate to a 'free vortex', in which the tangential velocity (v) increases as the centre line is approached, so that the angular momentum (rv) is constant).

Very small whirlpools can easily be seen when a bath or a sink is draining, but these are produced in a very different manner from those in nature. Smaller whirlpools also appear at the base of many waterfalls. In the case of powerful ones like Niagara Falls, these whirlpools can be quite powerful.

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