Vortices are fascinating to look at. You see them in hurricanes and in tornadoes. They form in stirred fluids, such as liquid, gas, and plasma. You can also find vortices in smoke rings, in the wake of a boat, and of a paddle. It's interesting to note that once a vortex has formed, it can move, twist, stretch, and interact in many different ways. Once in motion a vortex forms angular and linear momentum, energy, and mass. In a moving or changing vortex, the path lines are pulled and stretched into loopy, open curves. Watch this fun at-home science experiment video. I think it would make a fun party trick to do with your kids in the summertime.