Viatouch Teacher Articles
Science

The Pressure upon You
by Anjali Amit

Oh! The air around you. Do you feel it? Does it seem like you have the weight of the world upon your shoulders? If it doesn't, maybe it should. Air bears down upon you at the rate of 14.7 psi at sea level, which is 14.7 pounds per square inch if you are at sea level. That is a lot of pressure and it is exerted by something that is invisible. Here are some experiments for teachers to demonstrate air pressure.

Experiment One
What you need:
     A can with a lid
     A container, larger than the can, filled with water

What to do:
     Make several holes in the bottom of the can.
     In the lid make only one hole.
     Dip the can in the water container and let the water fill it up.
     With the can still in the container, place the lid onto the can.
     Put your finger over the hole in the lid, and slowly take it out.

What happens:
     As long as the hole in the lid is covered, the water stays in the can. Uncover the hole in the lid and the water pours out.

Why:
     Air pressure. When the hole in the lid is covered, the pressure of the air cannot act on the water. So the water stays. Uncover the hole, and the air can now reach the water in the can. The pressure forces the water out.

Experiment Two
What you need:
     A paper napkin
     A glass
     A bowl filled with water

What to do:
     Scrunch up the napkin and push it into the glass.
     Holding the glass vertical put it into the water bowl, open-end down.

What happens:
     Take out the glass and check. The napkin stays dry.
     Now, put the glass in the water again, but tilt it slightly.
     You will see a bubble of air escape, and water going into the glass.
     Take out the glass and check again. This time the napkin is wet.

Why:
     The glass is not really empty. There is air in it. The air prevents the water from coming in and wetting the napkin. When you tilt the glass some air escapes, creating an empty space. Water rushes in, and the napkin gets wet.

Experiment Three
What you need:
     A small-necked bottle
     A hard-boiled egg
     A hot-plate
     A pot filled with water

What to do:
     Fill the pot with water and place it on the hot-plate. Bring the water to a boil.
     Pour the boiling water into the bottle.
     Swirl it around, and then pour it out.
     Put the egg on the mouth of the bottle.

What happens:
     Even though the egg is larger than the mouth of the bottle, it quickly drops in.

Why:
     The hot water leaves steam in the bottle, which forces some of the air out. As the steam cools, it changes to droplets of water that take less space. This reduces the air pressure in the bottle. The greater pressure outside pushes the egg into the bottle.

Conclusion
     You can't see it, smell it, touch it or taste it. But this invisible medium is all around us, exerting its pressure upon everything on earth.

Bibliography
Branley, Dr. Franklin M. Air Is All Around You. NY: Harper Collins, 1962.
Devonshire, Hilary. Air. Danbury, CT: Franklin Watts, 1991.

Internet
http://kids.earth.nasa.gov/archive/air_pressure/
http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/circulation/air_pressure_p_1.html

Anjali is a children's book author whose first book,"Folk Tales From Rajasthan", was published when she was in college. Upon graduation she "sold her soul to Mammon"—went to work for a bank. She writes fiction, non-fiction, and edits technical documents. Her articles have appeared in various magazines. "Bedtime Stories from Around the World", her second book, was published a few years ago.