Dr Gadget's Science Machine
Vacuums do not really 'suck'

Marvin Esekielu, 11, tests a vacuum theory by sucking on a straw to get the liquid out. Cory Lum • The Honolulu Advertiser

Aloha. In the past few columns I’ve been discussing air pressure and vacuums. Most homes have a vacuum cleaner.

People say that a vacuum cleaner sucks up dirt. Does it really suck and does it use a vacuum? Have you ever used an upright vacuum cleaner and gotten a throw rug caught under it? When you hear the motor start to whine loudly, you have a vacuum!

If you are using a tank-type vacuum cleaner with a hose and you put your hand over the hose, you feel suction. That’s also an indication of a vacuum. The motor again makes a high-pitched whine.

But does a vacuum cleaner actually use a vacuum to clean? No!

A vacuum cleaner causes an air stream to move over the carpet’s surface. The air stream is directed up into a bag where the dirt particles become deposited. It’s like a tornado that picks up things in its path. If the vacuum cleaner were actually using a vacuum, it wouldn’t pick up anything! Why?

A vacuum is essentially nothing! How can nothing do something, like move dirt particles? It can’t!

Have you ever used a suction cup? Maybe you have a dart gun that has suction cups on the darts. If you shoot them at a wall, the darts "stick" to the wall. How do the suction cups work? When the dart hits the wall, the suction cup is flexible and bends. As it is being collapsed by the force of the dart, air is being squeezed from between the cup and the wall. The surrounding air all around on the outside of the suction cup pushes the dart to the wall. The vacuum is necessary for the surrounding air pressure to do the work of holding the dart to the wall.

Have you ever stuck a quarter to your forehead? Try it. Make sure it isn’t oily. Wash and dry your forehead if it is. Then press and rub a quarter back and forth on your forehead a few times. Release your hand and it should remain there. Bend your head forward. The quarter should still remain on your forehead.

Why? When you pressed and rubbed the quarter on your forehead, you squeezed the air out from between the coin and your skin. The air pressure outside of the coin holds it onto your forehead.

Try this: Get an empty 22-ounce plastic soda bottle. Remove the cap and make a hole in it that is just big enough for a soda straw to fit in. How? Put the straw in the hole and make sure most of it will be in the bottle. Seal the straw in the cap with a hot glue gun or drip candle wax on it. When the glue or wax has set, put the cap on the bottle and blow into the straw to make sure there are no air leaks. If it is air-tight, remove the cap and fill the bottle with water. Replace the cap.

Now, suck the water out of the bottle. Can you? No! Why? You can’t get the air out of the straw to make a vacuum, and the surrounding air can’t get into the bottle to push the water up the straw. Unscrew the cap and place it loosely on the bottle. Now suck on the straw. Does the water come into your mouth? The system has been restored. The surrounding air pressure pushed the water up into your mouth after you removed the air from the straw.

So, Nature really doesn’t suck! 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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