Why do you get a tornado if you stir tea really fast?

Have you ever tried stirring a liquid really fast with a spoon? Sometimes, it looks like it creates a tiny tornado in the cup! Why does that happen? We asked mechanical engineer Jacy Bird to help us find the answer. Got a question that has your brain spinning? Send it to us at BrainsOn.org/contact, and we’ll TEAm up to find the answer! See omnystudio.com/listener for privacy information.