What is the definition of a vortex in the context of water dynamics?

A vortex in the context of water dynamics refers to a pattern of flowing water where it revolves around a central axis, forming a whirlpool effect. This occurs when water moves in a circular motion, typically due to various factors such as the shape of the channel, obstacles in the water, or a change in the flow rate. The swirling motion creates a low-pressure area at the center of the vortex, drawing water in and causing a visible rotation.

In contrast, a still body of water does not exhibit movement or swirling characteristics, making it inconsistent with the definition of a vortex. Water at rest also lacks the motion necessary to create a whirlpool or any rotational dynamics. Similarly, a flowing river represents linear movement rather than the rotational nature of a vortex. Therefore, the characterization of revolving water forming a whirlpool accurately captures the essence of what defines a vortex in hydrodynamics.