“Blow Hard,” Friend, Sept. 1991, 26
Blow Hard
To do this experiment, you will need: a thread spool, a straight pin, a piece of cardboard, and scissors.
Cut the cardboard so that it is larger around than the end of the spool, and put a pin through the center of it (see illustration). Then place the pin inside one end of the spool, and blow through the other end.
Can you blow the cardboard off?
What happened? The air that you blew through the spool’s hole escaped between the end of the spool and the cardboard, causing a low air pressure between the cardboard and the spool. The higher air pressure on the other side of the cardboard pushed it toward the spool.
Could you blow the cardboard off if you blew through the spool towards the floor? If you stop blowing, will it fall? Try it and see!
Could you blow a Ping-Pong ball out of a funnel if you held the funnel so that the ball would not fall out? Try it and see!