At work we have a FLIR E60 thermal imaging camera. It’s an amazing little device and I want very much to take it home some days (I’d bring it back, I just want to see things). One day while we were setting up I happened to point it at the cup of coffee on my desk. What I saw was something I didn’t expect, but I should have.
I had always assumed that my coffee was pretty static and once you had set it down and left it for a few minutes all of the internal flows would settle down. Boy was I wrong. The hot coffee forms unstable upwellings in the cup and cools once it reaches the air at the surface, then it sinks back down. The effect is like watching the top of a lava lamp, and for the exact same reasons.
I had already printed out an adapter to mount the camera to a tripod and decided that I should take a movie of the process.
Nothing happens at the end. Don’t wast all your free time.
At about 2 minutes in I gave the coffee a stir. It’s pretty neat to watch the vortex slowly fade into the unstable upwellings again.