Contrary to popular belief, lighting a match in a bottle does not
create a vacuum by using up oxygen. Although the flame burns up oxygen,
it produces an equal quantity of carbon dioxide, another gas. Instead,
the fire just heats up the air in the bottle. The air stays at
atmospheric pressure, which means that the density must go down when
the temperature goes up, since the pressure is approximately
proportional to the product of density and absolute temperature. You've
got plenty of time to seal the bottle before it cools down. When it
does cool down, the pressure will then drop to less than atmospheric
pressure, so you'll have a partial vacuum.
Probably the easiest way to create a vacuum at home is with a
suction cup. If you press a suction cup flat against a wall and pull
back, the inside of the cup will contain a vacuum. (This is why the cup
sticks to the wall.) You can also create a vacuum inside of a syringe.
If you seal the syringe up and pull back the plunger, there will be a
If you want to create a vacuum in something larger than these, try
hooking a container up to the hose attachment of your vacuum cleaner. A
household vacuum cleaner should be able to produce a partial vacuum.
Of course none of these 'vacuums' are close to being completely
empty of molecules, but they can have pressures much less than the
(republished on 07/18/06)