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Name: Lorraine
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 2000-2001


Question:
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?


Replies:
Hello,

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.

AK


Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory
Argonne, IL 60439


Dear Lorraine-

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 water vapor.

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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