Putting pressure on a bottle makes it want to blow

Aloha! Have you ever seen someone open a bottle of champagne and heard the cork "pop"? Why does it pop?

The reason: It is under a great deal of pressure from carbon dioxide gas in the bottle. As the gas is released and strikes the air outside, it is like a mini thunderclap.

• It is possible to have a container of air that is pressurized. You can do this with an empty plastic soda bottle and a cork. When the soda bottle is empty of soda, it is still full of air. Put the cap on the bottle and squeeze it. The sides of the bottle do go inward to a point, but then they stop. Why? Because you have pressurized the air inside the bottle. It is compressed! This means that you have done work on the air particles as you pushed them into a smaller space.

What happens when you release the bottle? Do the walls pop back out? Why? The force you put on the bottle when you pressurize it causes the air particles to move with more force in their smaller volume. When you release your grip on the bottle, the air particles give back the work you put in as they move the walls of the bottle back out to their original position.

• Now uncap the bottle and find a cork that will fit in the mouth of the bottle. You don't want it too loose nor too snug. This may take a bit of trial and error. With the cork in the bottle, point it toward a neutral direction (away from any people or breakable objects) and squeeze the bottle real hard. Did the cork fly out? If it didn't, maybe it is too loose. Try putting a couple of turns of masking tape on it to make it fit more snugly. Why does the cork fly out of the bottle?

The air inside the bottle is being compressed by your force. You were doing work on the air. The cork is a weak point in the system. All of the force you put on the air when you squeezed the bottle momentarily compressed it. As the air pressure increased, the cork let go - remember, it's the weak point. The compressed air pushed the cork out of the bottle. The cork should fly at least three feet. It shows that compressed air does have force.

• Nature exhibits fierce examples of air pressure in wind storms such as hurricanes and tornadoes. Farmers have reported pieces of straw, the grass that is used for hay, driven into telephone poles. Imagine - this straw is as flexible as the straw that makes up a broom! Imagine driving a piece of broom straw into a piece of wood! Here's one last thing to try if you want to investigate how it's done.

Get a soda straw and a potato. Place the potato on a level surface like a table top. Hold the soda straw in your clenched fist tight enough so it does not move, but not so tight that you bend the straw. Make sure both openings are uncovered. Now strike downward at the potato and see how far you can drive the potato into it. Were you able to go through the potato?

Now do it again. This time cover the hole in the top end of the straw with your thumb. Again strike downward at the potato and see how far the straw will penetrate. How far were you able to go? Was it farther than last time? It should have been! Why?

This time you pressurized air inside the straw. The air built up in it as you struck downward. The compressed air helped the straw absorb the shock of striking and entering the potato. Straws of grass also have a small amount of hollowness in each piece. Perhaps this is a part of what enables them to be driven into telephone poles.

Until next time . . . a hui hou!

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"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."