Sunday, March 4, 2001
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Posted on: Sunday, March 4, 2001

Dr. Gadget's Science Machine
Principles of air pressure demonstrated

By Joe Laszlo
Special to the Advertiser

Kamehameha School second-grader Ikaika Meyer, 7, floats a ping pong ball to demonstrate the Bernoulli effect.

Richard Ambo • Honolulu Advertiser

A fun look at science working in the world around you, plus a cool gadget or experiment to test it out.

Aloha! In past columns I have discussed some ideas about vacuums and air pressure. One of the most unusual ideas about air is that of Bernoulli. He discovered that if the speed of a fluid moving over a surface is increased, the pressure decreases. This idea has been used in everything from atomizers to airplane wings. Here are a few gadgets you can make to test this.

Get a strip of paper about 3 inches wide and 6 inches long. Make a small fold along one short side. Hold the paper under your nose above your upper lip. Blow along the paper. Which way did it go? Did it rise? Good. Why? Because it rode on a cushion of air from your lungs.

Now move the paper so that the fold is just below your lower lip. If you blow on the paper now, what do you think it should do? Try it! Which way did the paper go? It rose again! Why? Your breath moving over the surface of the paper caused the pressure of the air above the paper to become lessened. The air pressure under the paper pushed it up!

Stores that sell vacuum cleaners often have a display where they use a tank-type vacuum cleaner with a hose on the end that is blowing air. A beach ball is often suspended in the air stream, and it seems to wobble back and forth. You can do the same thing with a piece of tubing or a bendable soda straw and a ping pong ball.

Hold the tubing in a U shape and put one end into your mouth. Hold the ping pong ball over the other end of the tube and blow. Release the ball. It should be suspended in the air. Your breath is holding it up.

But notice it wobbles back and forth? Why? This is again a matter of lessening the air pressure first on one side of the ball because the air is moving faster along that side of the ball. The ball moves in the direction of the lesser pressure. With the ball to one side, the air is now moving faster on the other side and the pressure becomes lessened on that side.The ball wobbles back the other way. All of this happens in less time than it takes to talk about it.

One of my favorite gadgets uses a funnel and a ping pong ball. I have a student blow into the funnel while holding the ball momentarily, then remove the hand holding the ball. I tell them to blow the ball out of the funnel. Try it. It is impossible. As long as you have an air stream going in the funnel, you can’t blow the ball out of it. Why is this so? What is happening?

Again, you have succeeded in causing the air to move very fast between the wall of the funnel and all sides of the ball. You have reduced the pressure within the funnel. So air pressure pushing in on the ball holds it in place. When you stop blowing, the system goes back to the way it was originally, with all pressures being equal. The ball has nothing to hold it in the funnel, so it rolls out. Bernoulli’s principle works whenever you want to test it! Until next time . . . a hui hou!

Write to Dr. Gadget with a question or comment and we’ll put your name in a drawing to have your picture taken with a gadget. Sorry, not all letters can be used. Mail your letter with your name, age, school, name of parent(s) and telephone number, to: Dr. Gadget, c/o The Honolulu Advertiser, P.O. Box 3110, Honolulu, HI 96802, or fax 535-8170. You may send e-mail to only if you’re 13 or older.

"Dr. Gadget’s Science Machine" is written by Joe Laszlo, a retired science teacher and winner of a Presidential Award for Excellence in Science Teaching. His column alternates in this spot with "Hawaii Nature Squad."

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