Fool  The Spool

  As you do the next activity, can you figure out how the pressure changes?

  How does this help airplanes stay in the air?

Materials: straight pin, 3x5 index card or business card, large spool
Stick a pin through the middle of a card from below. Place the spool over the pin. Hold the card and pin in place with one hand; hold the spool with the other. Blow strongly through hole in the top of the spool and let go of the pin and card. What happens? Hint: Make sure the spool has only one main hole. If others exist - even pin holes - tape them closed.

In both activities, air lost pressure and stopped pushing as hard. This happened because you blew the air, and it had to squeeze between or around the objects. As it squeezed through, it sped up, lost pressure, and stopped pushing as hard. As air squeezed between the spool and card, it moved faster, and its pressure dropped. The air pressure below the card didn't change; it continued to push as hard as it always does. It held the card in place even though you were blowing hard.

Bernoulli tells us that air rushing over the top of a curved surface has less pressure than the air traveling across the bottom of the surface. An airplane wing is curved, though not as much as the Ping Pong ball. The air that rushes over the top of this curve moves with more velocity than the air on the bottom. We find that there is less air pressure on the top than the bottom.

An airplane wing is designed based upon Bemoulli's discovery. This tells us that when air is still, it has more pressure than air in motion. If air must travel over an obstacle, as motion increases, the air pressure decreases. In motion, the pressure or exertion of that air becomes less. The faster the air moves over a surface, the less pressure it has on the object.

THE AIR RUSHING OVER THE TOP OF THE WINGS ALLOWS THE AIR UNDERNEATH TO "LIFT" OR PUSH AN AIRPLANE INTO THE SKY!

These experiments and other similar air pressure experiments may be found at:
http://www.nasm.si.edu/exhibitions/gal109/LESSONS/TEXT/TEASERS.HTM