Editing Vortex ring (section)

==Structure==
[[File:Vortex ring.gif|thumb|250px|right|Flow around an idealized vortex ring]]
In a typical vortex ring, the fluid particles move in roughly circular paths around an imaginary circle (the ''core'') that is perpendicular to those paths.  As in any vortex, the [[velocity]] of the fluid is roughly constant except near the core, so that the [[angular velocity]] increases towards the core, and most of the [[vorticity]] (and hence most of the energy dissipation) is concentrated near it.{{Citation needed|date=June 2021}}

Unlike a [[sea wave]], whose motion is only apparent, a moving vortex ring actually carries the spinning fluid along.   Just as a rotating wheel lessens friction between a car and the ground, the poloidal flow of the vortex lessens the friction between the core and the surrounding stationary fluid, allowing it to travel a long distance with relatively little loss of mass and kinetic energy, and little change in size or shape.  Thus, a vortex ring can carry mass much further and with less dispersion than a jet of fluid.  That explains, for instance, why a smoke ring keeps traveling long after any extra smoke blown out with it has stopped and dispersed.<ref>{{citation | first=G.K. | last=Batchelor | author-link=George Batchelor | title=An introduction to fluid dynamics | publisher=Cambridge University Press | year=1967 | isbn=978-0-521-09817-5}}</ref> These properties of vortex rings are exploited in the [[vortex ring gun]] for riot control, and vortex ring toys such as the [[air vortex cannon]]s.<ref name="APS">[http://www.physicscentral.com/experiment/physicsathome/cannon.cfm Physics in a Toroidal Vortex: Air Cannon] Physics Central, American Physical Society . Accessed January 2011.</ref>