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Q & A: Shrinking Cans and Shattering Plates

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Most recent answer: 10/22/2007
Q:
I was reading one of your answers about heating a pop can and putting it in water - I’m thinking this is the typical experiment done lately - that is: heating water in the can to boiling - then inverting the can and bringing it (open end down) down on the surface of cold water. I assumed that the water vapor condensed leaving a partial vacuum which prompts the collapse of the can. And so I assumed that this is a demonstration of air pressure. In your answer to a student (who described her experience as heating the can and throwing it into a pan of cold water - and it exploded) you said the can responded to changes in temperature on the metal - that it was not air pressure. Are these two different demonstrations?
- Anonymous
A:
Yes, these are two totally unrelated experiments. In the one that you are describing, the can shrinks due to the decreasing air pressure as the air cools down. The experiment from the previous question refers to a phenomenon that has to do with the material itself. No air is ever trapped in the can, so changing air pressure won't affect it. The metal in the can itself changes temperature so quickly that the can breaks.

This is the same phenomenon as if you were to accidentally set a plate on a hot stove burner (making the plate very hot), then set cold or frozen food on it. The temperature of the plate changes so quickly that the plate shatters.

-Tamara

(published on 10/22/2007)

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