Last time, I left you with a challenge. We put a little sand into a glass of water and stirred it. Instead of moving to the outside edge, as we might expect, the sand gathered in the center of the glass. I left you with the challenge of telling me why.

Congratulations! Several of you got the right answer, and several more got it at least partially right.

This experiment is Subscriber Only content.

Subscribe Now, and get full access to this experiment, and hundreds of other experiments and videos.