Two Soda Cans Explain Why Airplanes Fly

Lay a row of naked straws parallel to each other on a smooth tabletop. Place two empty soda cans on the straws about an inch apart. Lower your nose to the cans and blow hard through the space between the two cans and *clink* they should roll toward each other and touch!

Why does this happen? When air moves, the pressure decreases. This creates a lower (relative to the surrounding air) air pressure pocket right between the cans. Recall that higher pressure pushes, and thus the cans clink together. Just remember – whenever there’s a difference in pressure, the higher pressure pushes.

What kinds of questions can you ask about this project?  For example: What types of cans work and don’t work?  How much air pressure you you really need – would a hair dryer be a better choice?

1 Comment

  1. Beth Said,

    February 11, 2009 @ 12:19 pm

    Thanks for posting such wonderful ideas to get kids excited about science!! This one is such a great experiment demonstrating Bernoulli’s principle! I used windbags in my classroom to teach this same concept on the movement of air!