Tuesday, April 5, 2011

Experiments in Atmospheric Pressure

From the Bizarre Labs website:

Collapsing a can with air pressure

Atmospheric pressure is strong enough to crumple a metal can. This can also be done using an aluminum soda (pop) can. Put a little water in it (app. 3cm) and heat on a hot plate until it begins to steam. If you must do this over a gas or other flame, don’t use a very high flame or an empty can; the paint may burn or, worse, the aluminum may melt. Using tongs, quickly flip it upside down into a small tray of ice water, which should be 6 or so inches (15cm) deep. The water will prevent the outside air from entering. A little of the ice water will be drawn up into the can, but not enough to equalize the pressure, and the can will crush.

Egg in a bottle

There are plenty of things to do with eggs, one being the egg in the bottle trick. Use a shelled, hard-boiled egg. The egg needs to be free from cracks in the white and smooth. Find a bottle with a neck just small enough that the egg won’t fall in (a carafe, milk bottle, or some baby bottles–possibly an ice tea bottle). Wad up a little piece of paper and drop it in the bottle (you can also use 2 or 3 wooden matches). Light the paper or matches, allow to burn out, and immediately put the egg in the bottleneck, where it should be sucked in (making a very interesting sound in the process). Actually, the egg isn’t sucked in, it’s pushed. The fire heats the air, causing it to become less dense and to rise out of the bottle. This causes a decrease in air pressure inside the bottle. The higher pressure outside the bottle pushes the egg in.

A reader recently reminded me that you can easily get the egg out again by turning the bottle upside down and blowing into it very hard. When you take your mouth away, the egg should pop out due to the increased air pressure in the bottle.