See It Through Straws

[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:

• 2 plastic drinking straws (or one straw cut in half) • a cup of water

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. Hold 1 straw straight up (vertical) with the lower end submerged in the cup of water.
4. Hold the other straw level (horizontal) with one end in your mouth and the other end touching the top end of the other straw. Make sure that you hold the two straws at a right angle to each other.
5. Blow air through the horizontal straw so that it rushes straight across, not into, the tip of the vertical straw.
6. Watch the level of the water in the vertical straw.
7. Move the end of the horizontal straw around as you blow and see how this changes the height of the water in the vertical straw.

Useful information:

The air of our atmosphere exerts pressure on everything around you, and on you. When you blow air through the straw your cheeks puff out because there is more air pressure inside your mouth than outside. When you inhale quickly your cheeks collapse inward because there is less air pressure inside you mouth than outside. You may wonder why a piece of paper doesn’t fly into your face if you blow straight on it, vertical to the page, than along, or parallel to it. The big difference is the angle of air flow. The air must be moving parallel, or nearly parallel, to the surface to make the pressure lower. You can see this in when you change the angle at which you blow air across the vertical straw, which changes the height of the water in the straw. 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.