To do this demonstration, play it safe and do it under adult supervision.

If you have ever seen a can crush when it is being heated and then turned upside down and placed into a cold water bath, you have probably witnessed the Crushing Can demonstration.

If you have not, you can do the demonstration by doing the following:

Observations:

First, obtain an empty pop can and add a small amount of water to it.  Then, put this pop can with water on a hot plate and wait until you can see the water vapor coming from the can.  Then, quickly, turn the can over and submerge it into the a cold water bath.  If you have done the demonstration correctly, you should notice that the can has made a loud noise and that it has collapsed.

Why does the can collapse?

Explanations:

What happens to the water throughout the demonstration:

Well in the beginning, we have liquid water.  Then as it is being heated on the hot plate, it is heated which causes the water to go from a liquid to gas.

As the water is continuing to condense to a liquid, the can is being filled with gaseous water, water vapor.  This water vapor is a gas which means that it expands.  This gas expands throughout the can and outside of the can.

So why does the can crush?

Since many students such as those discussed in the students' ideas page have a hard time understanding this phenomena, we will explain why this phenomena occurs by explaining two main ideas that are needed to explain why the can crushes.
 

Main Idea 1-The changes that the water undergoes throughout the demonstration

The first thing that we must realize to explain this phenomena is that the water inside the can is condensing and causing the can to be filled with water vapor, gaseous water.  If you remember from the phases of matter, an increase in pressure can be considered an physical force that causes water to change into gaseous water.

When the can is sealed and cooled when it is submerged in the cold water bath, the water vapor condenses back to a liquid inside the can, which takes up less volume than the water vapor.  This in turn lowers the pressure inside the can.  It is important to note that the pressure inside this can is now less than the pressure outside the can.

Main Idea 2-Differences in Pressure

The difference in pressures of the inside of the can and the outside of the can.  On the outside of the can, atmosphere pressure is remaining constant and is acting on the can.  As for the pressure inside the can, it has decreased which means that the pressure outside is greater than the outside pressure.  As a result, the can is crushed by the collisions of outer air molecules with the surface of the can.