Baba B.

asked • 03/02/23

Can Crush by Air Pressure Experiment

If you put a can with water at its base over a hot plate and allow the water to heat. Once Steam is visible from the top of the can, and quickly flip the can upside down into a bowl of water with gloves or tongs, the can will be crushed by the atmosphere.


I know by heating the can, we boiled the water inside it. The process of boiling turned the water into vapor. And since the water vapor molecules are much more spread out than the water molecules, they take more space and are forcing the molecules of air out from the can. And when we put the can in the cold water, we suddenly cooled it. That cooling caused the water vapor in the can to condense, creating a partial vacuum. Because of that, the pressure outside of the can became much greater than the pressure inside, and that pressure difference crushed the can.


However, my point of confusion is...



How may someone calculate the air pressure of which the can is crushed before or after impact?


Heidi T.

Unless otherwise specified, you can probably assume the air pressure is the standard air pressure. Air pressure changes with ambient temperature and elevation above sea level (and a few other things) but for the purposes of most experiments like this in a basic course, using the standard is acceptable.
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03/04/23

Navin P.

Adding to Heidi's point, it is also reasonable to calculate the pressure INSIDE the can. This will require using PV=nRT two times. First use it at to get the number of moles that remain in the can, using n2/n1=T1/T2. Now since final volume and temperature will become the same as it was at the start of the experiment, use P2/P1=n2/n1 again to get the final pressure inside. The difference between the external pressure (see Heidi's comment) and the above pressure gives you the air pressure that crushed the can.
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03/12/23

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