Sunday, February 4, 2001
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Posted on: Sunday, February 4, 2001

Dr. Gadget's Science Machine
Air pressure has impact on many things

By Joe Laszlo
Special to The Advertiser

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

Aloha! In the last column we discussed air. Living at the bottom of an ocean of air, almost everything is influenced by the pressure of the air. Here are more thoughts about air and air pressure:

How do we know air has pressure? There are a lot of things you have probably experienced at one time or another that are caused by air pressure. For instance, have you ever ridden in an elevator to the top of a tall building and had your ears "pop"? What causes the pop?

Ears are very sensitive to pressure changes. To keep the air pressure balanced on both sides of your ear drum, there is a tube that goes from the back of your throat to the inner ear, and opens on the other side of the ear drum. It’s called the Eustachian tube.

If this tube becomes "pinched down," such as when you have a head cold, air doesn’t get into the inner ear as quickly as it normally does. If there is a rapid change in pressure, such as when you go up in an elevator quickly, the balancing of the air pressure on both sides of the ear drum is what makes that "pop" sound.

Why does air have pressure?

Think of it this way: All material in the world is either a solid, liquid or gas.

Let’s consider water. Does water have weight? Of course it does. A five-gallon bucket of water is about 42 pounds. If we were to freeze the water into ice, would it still have weight? Of course.

If we heated the water and turned it into water vapor, a gas, would it still have weight? Of course. Just because we separated the water molecules by heating, we didn’t take away their weight!

The same thing is true for the gases that make up air. Pressure is weight divided by area. The pressure of the air at sea level it is 14.7 pounds per square inch. Draw a square inch on the palm of your hand with a piece of chalk. There is 14.7 pounds pushing on it!

Why don’t you notice the pressure on your palm like you do in your ears? You were born into the environment that has this pressure. You have pressure inside your body pushing outward to balance it. Your body learned to compensate for the pressure from before you were born.

But your ear only relies on the air pressure on either side of the ear drum. There’s nothing pressurizing it from the inside like your body does for your skin.

Here’s a quick experiment to test out some of these ideas:

Get an empty plastic soda bottle and remove the cap. Squeeze the bottle hard and press the mouth of the bottle onto the underside of your arm. Hold it there while you gradually stop squeezing it. Did the bottle "stick" to your skin? It should have, but why?

The answer is that the surrounding air held the bottle to your arm. Also, you have pressure inside your body pushing outward to balance the 14.7 pounds of air pressure pushing on you.

The bottle removed some of the air pressure, and your skin was pushed into the opening by your internal pressure. This helped to stabilize the bottle on your arm. As air seeped back into the bottle, the pressure became equalized and the bottle fell off.

Here’s a wild thought: If someone were to remove all of the air from around you all at once, you would explode like a kernel of popcorn. Wow!

"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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