In fluid dynamics, the field of science that studies the movement of fluids (note that a “fluid” can be also a gas), a vortex is defined as an area of a fluid where the motion of the fluid takes place around an axis, which can be straight or curved. Vortices and their effects range from the quantum realm and the world of microorganisms, to water draining down a toilet, tornadoes, hurricanes, and Earth-sized storms on other planets. Bodies travelling through a fluid generate vortices. These vortices can produce a drag on motion. This vortex drag is reduced in airplanes by appropriate wing design, while migrating birds overcome this drag by flying in a “V” formation. On the other hand, the production of vortices is exploited by insects such as bees to make their flight possible. The study of vortices is important and has generated and will continue to generate many practical applications.
In the cool video below, Dianna Cowern (Physics Girl) produces dual vortices in a pool which can be followed by looking at the shadows they project on the bottom. She also uses food coloring to demonstrate that they are connected forming a half circle!