Heating and Air Pressure
i put a few mL of water into a cola can and eated it
until the water boiled. i then inverted the can over a tray of icy
water. the can collapsed into itself, why did this happen?
When a soda can with a few drops of water in it is heated, water evaporates
and pushes the air out. What remains is mostly water vapor with a little
nitrogen, oxygen, and other constituents of air.
If the heated can is immediately inverted and pushed into a cold medium
(such as ice water), the water vapor in the can condenses and the pressure
inside the can drops quickly. A relative vacuum inside the can is thus
created. Air cannot get into the can. Water begins to flow into the can
but the condensation of the water vapors in the can occurs at a faster
rate. The can implodes as a result of the pressure imbalance: atmospheric
pressure on the outside and relative vacuum on the inside.
Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory
Argonne, IL 60439
Your experiment with the can and boiling water demonstrated the power of
air pressure. When you boiled the water in the can, you expelled the air,
and replaced it with water vapor, the evaporated water from your can. When
you heated the water, the vapor pressure over the water became greater than
the air pressure, and that "pushed" the air out of the can, along with some
When you inverted the can, you cooled the vapor to less than its
condensation point, and the vapor turned back to liquid. This left a vacuum
inside the can, and the outside air pressure crushed the can, due to the
difference in air pressure from the inside and outside of the can.
Wendell Bechtold, Meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO
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Update: June 2012