How does a cup move on its own when pouring hot water into it?

[mgb_phys]

You use the same principal in oil bearings. A small oil pump pressurizes the oil and the load floats on an almost frictionless film of oil.
You can push a 200ton telescope around with your hand.

 

[rainnw]

Here is the phenomena in action:



This always happens at a certain asian restaurant we visit, and takes everyone by surprise.

I finally was able to reproduce it by putting in very hot tea and letting it sit for a while. Its a good party trick.