In: Physics
There is an experiment that demonstrates the first law of thermodynamics by using a tin can. The problem is I don't understand why there is a work done. The link to that video is https://youtu.be/jNPUCmkKiE4?list=WL&t=180 . Can someone explain to me why the tin can suddenly imploded?
See when the can is heated, it's temperature increases. When you put it into water, it's temperature decreases and pressure also decreases. Therefore the force exerted by gas inside on the walls of the can becomes less than the force by outside pressure. As a result, the can implodes.
(You would ask then, why did it not explode when it was being heated. The answer is, when we increase temperature, it's volume may increase or it's pressure may increase. What is happening here us the can is not completely sealed. So when it was heated, it's pressure remained same and some of the gas leaked into air. So that PV=n'RT.
When you suddenly cool it, there is no time for outside gas to leak in. So V and n remains constant. Therefore if T decreases, P decreases and can implodes as stated above)
As for work, since the gas exerts force on the wall and the wall points move in, there is force and displacement. Wo work is done. You can also see that this work done is negative (force directed outside and displacement towards inside).