When you crush a can,why does it always crush inwardly and what gas law supports that?
Cans crush inwardly because they are designed that way. They are very strong when it comes to containing pressure, so they will not, by design, bulge outward. However they are not intended to resist inward pressure and so will collapse in that direction readily.
You may be thinking of this experiment, in which an empty can is made to collapse due to atmospheric pressure alone. In this case, the can is manipulated so that the number of air molecules inside the can is lowered by heating the air inside the can. Then the can's opening is blocked, and the air within is cooled, causing the molecules to contract together. This greatly lowers the air pressure inside the can. Meanwhile, atmospheric pressure outside the can remains constant. This results in an imbalance, with more pressure pushing inward than outward, and the can collapses inward.