Dr. Gadget
Here's a way you can tell whether air is really there

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

Aloha! Do you know that you are living at the bottom of an "ocean" of air? Air is a mixture of many gases. You might know that oxygen is one of them. Oxygen is needed by most living things. Other gases that make up air include nitrogen, hydrogen, carbon dioxide and water vapor, just to name a few.

McCain Dannis, 11, blows into a bottle, learning about air pressure as Dr. Gadget watches, at Central Intermediate School. Cory Lum • The Honolulu Advertiser

Air is everywhere on this planet, except in what is known as a vacuum, a space that is empty of matter. But no vacuum that is made by people is perfect. There are always still some air particles in it.

Let’s explore air pressure. Have you ever filled an empty bottle by holding it under water? Did it fill easily? What did you notice happening at the mouth of the bottle you were trying to fill? You should have seen bubbles. What caused these bubbles?

If you said the air coming out of the bottle, you are correct. In order to fill an "empty" bottle, you have to first empty out the air!

Here’s something to try with a soda bottle and a balloon: Push a balloon into the soda bottle and stretch the mouth of the balloon over the rim of the mouth of the bottle.

Now try to blow up the balloon. You’ll huff and you’ll puff, but you won’t get the balloon blown into the bottle. It’s impossible. Why? Because you can’t empty the air out of the bottle. The balloon is blocking the only place for the air to get out. You can’t put more air into the balloon in the bottle until you get rid of the air that is already in the bottle! Got that?

How can you get rid of the air? Try this: With a nail, punch a hole into the bottle (it has to be a plastic bottle, not glass!) near the bottom. (If you need help, ask a grownup.) Now try again to blow up the balloon. Put a hand near the hole as you are blowing it up. Do you feel the air coming out of the bottle? You should.

If you put the bottle into a container of water so the hole is underwater while you blow up the balloon, you would see air bubbles in the water.

Now try this: Get another plastic soda bottle and fill it up with water. Turn it over and empty it out as fast as you can. Time yourself: How long did it take?

Refill the bottle. This time when you turn it over, whirl the bottle in a circular motion to get a whirlpool going in the water. Time yourself again. Did it empty faster this time? It should have, but why? The answer is that this time you were able to get the air into the bottle to push the water out!

Air needs to get into the bottle. Gravity does want to pull the water out, but the opening is so small that air can’t get in fast enough. But when you added the whirlpool, it caused a tube of space to form in the center of the remaining water that helped to draw air up into the bottle. More air in, more water out!

Here is one last thing to try: Refill the bottle and put an index card over the mouth of the bottle. Turn the bottle over slowly. Did the water come out?

The air pressure that we all live in at the bottom of this "ocean of air" pushed up on the index card. That’s why it wouldn’t fall off. The index card should have acted as a barrier and kept air from coming into the bottle. No air in, no water out!

I’ll write more about pressure in future columns. Air, air, everywhere! Until then · a hui hou!

Do you want your picture to appear in this column? If you write to Dr. Gadget with a question or comment, we’ll put your name in a drawing to have your picture taken with a gadget. 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 ohana@honoluluadvertiser.com 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 "Hawai‘i Nature Squad."

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