Ever wonder how an atomic clock keeps time so accurately? Or how a GPS uses that time to calculate its position? This video uses jello as a prop to explain exactly that. There are a few details in there that are glossed over a bit, so I don't think I'll be building my own atomic clock based on this, but I have a better idea of how its done. I had no idea that they've gotten the guts of those things down to such a small package.