Fun exercise to demonstrate bernoullis principle that I love to whip out. Take two pieces of paper and hold them from the top so that they're hanging parallel to each other. Blow air between them. Most people expect them to go apart due to the air coming at them, but the higher velocity causing lower pressure means the static air on the outside of the papers actually pushes them together.

I went to a science center that had a demonstration with two heavy stone balls and an air cannon. The cannon was powerful enough that the balls actually touched. Mind blowing.