You might already know that hot gas rises and cold gas falls. So what happens to a gas located in between a hot plate and a cold plate? It simply circles around between the two plates, hot air rises towards the cold region, its temperature decreases and it falls back down towards the hot plate and the cycle goes on.

This phenomenon is called Rayleigh-Bénard convection (or instability). Structures of upwards and downwards moving gas are called "cells", their shape, size and number depend on the temperature difference, the distance between the plates, the properties of the fluid and the gravity field.

Enjoy these short clips of hot air rising and cold air descending. Created with (1) Physics Results Explorer and (2) Physics Simulation Review. Variable transparency was used to hide the color green so as to see mostly the hot red and cold blue regions