Hobbies And Interests
You Versus A Piece of Paper
Air pressure of 14.7 psi equals about one metric ton of air pressing against each square foot. Human bodies are designed to push back out with an equivalent amount of pressure, which explains why we don't get crushed by the weight of air. To demonstrate how "heavy" air actually is, you'll need a large piece of paper (at least a square foot), a thin ruler or yardstick and a table. Clear the top of the table and put the thin yardstick on top, with half of it hanging on the edge. Position the paper in such a way that it covers half of the yardstick laid on the table. Make sure the sheet lays as flat as possible against the surface. Next, show that pressing down on the yardstick's free end does not lift the paper, but instead bends or breaks the stick.
Lift Heavy Books with Air
This demonstration shows how strong compressed air can be. For this experiment, you'll need one or more heavy books and a tough balloon or inflatable pillow. Start by laying the balloon flat on the table. Next, place the books on top, but keep the balloon's open end free. Begin blowing air slowly into the balloon. If you have a small basketball pump, you can also use it to inflate the balloon. Observe as the books lift gradually off the table, supported by the compressed air.
The Egg-in-a-Bottle Experiment
This experiment calls for a peeled hard-boiled egg, a jar with a mouth slightly narrower than the egg's diameter, some paper and matches. To start off, set a small piece of paper on fire and drop it into the jar. Next, place the egg on top of the jar's mouth and watch as it gets "sucked" inside. What actually happens is that the fire heats the air in the jar, making it expand and escape. You then place the egg on top and wait for the flames to die. As the jar cools, the air pressure inside it drops. The greater atmospheric pressure outside then pushes the egg into the jar.
The Collapsing Can Experiment
In this experiment, students will see that air pressure is strong enough to crush an aluminum can. Prepare a used and empty soda can, a sufficiently large container, ice cubes, water, tongs, and a Bunsen burner. Dump the ice cubes into your container and fill it with water. Let it cool for a while. Next, take your empty can and pour a little amount of water, enough to boil a little and condense. Pick it up using tongs and hold it over the burner until steam comes out. Allow it to boil for about 30 seconds, then quickly dunk the can upside down into the ice water. This crushes the can instantly. What happens is that the water vapor in the can pushes out the air, but when it is suddenly immersed in cold water, the vapor condenses, creating a partial vacuum. Because atmospheric pressure exceeds the pressure inside the can, the can collapses on all sides.