Have a plate, a pool, and some food coloring? In this experiment, Physics Girl Dianna Cowern makes strange black circles form by briefly dragging a plate through the pool. On a sunny day in still water, those black circles can be seen traveling the length of the pool. What’s creating this unique phenomenon?
File under vortices and DIY: Those circles hint at a half vortex spinning below the water’s surface. Watch as she adds food coloring to its ends and explains all of the details, then be sure to try this physics experiment the next time you’re at the pool in the sun.