Ping Pong Ball Squeeze

[15 Minutes]

How does a 747 lift itself off the ground? Or a Helicopter? Or a bird? Balloons fly because they are lighter than the air, but a plane is much, much heavier, often weighing several tons. The plane, the helicopter, and the bird use their wings and the rush of the wind to fly. Try this activity to show how the rushing of air can lift an object.

You'll need:

• a plastic funnel, between 2 and 4 inches wide • a ping pong ball or similarly sized light plastic ball

What to do:

1. If possible, print out these directions. Read them through before you begin.
2. Gather everything you'll need and always remember science safety.
3. Place the ping-pong ball on a level table so that it doesn’t roll.
4. Hold the plastic funnel upside down over the ping-pong ball. Keep the rim about ¼ inch above the table.
5. Blow into the funnel. Watch the ping pong ball and see how it moves. It will rise up off the table.
6. Move the funnel up and down and see how the movement of the ball changes.
7. Try to move the funnel sideways and see if the ball moves sideways with it.

Useful information:

When air moves across a surface it exerts less pressure than if the air was not moving. The greater the air speed the less the pressure. And air pressure can move an object. If an object has more air pressure on one side than the other it is pushed in the direction of less pressure.
Can you see how the air flow in is causing the ping-pong ball to rise up off the table? Think about where the air is squeezed as it moves down the funnel and around the ping-pong ball. Since the air behind it is pushing the squeezed air it cannot slow down. In fact, it has to move faster, and this lowers the pressure felt by objects that are squeezing the air. How does an airplane’s wing, a bird’s wing, or a helicopter’s rotor use the speed of air to fly? When you look at a wing it may not be obvious, since it looks like there is nowhere that the air would not be moving very fast. The secret is in the curved surface of the top part of the wing, which is far less flat than the underside of the wing. When air hits a smooth curved object, like a ping-pong ball, the air nearest the object is forced to move a longer path around it than air that is further away. Yet, all the air, both near and far from the ball, is being pushed along by the air behind it, forcing the air near the object to speed up. The air near the object is squeezed. The lifting pressure may seem small when you see it in this activity. But on the special shape of a wing it is more than enough to lift a 747 with all its passengers safely into the air.