Here’s a cool trick to do in a pool that will show off your physics knowledge to your family. Dragging a plate in the water can cause two black dots to move along the bottom of the pool at the same time.
It’s caused because the motion creates two small vortexes. It’s the same natural phenomenon that cause hurricanes and tornadoes, etc. But how do they form? Why do the vortexes move together? And why do they create clear black spots? I’ll leave that to Physics Girl to explain!