Experiment with Bottle: Hot Air, Freezer & Pressure

[Bzdzwongul]

Hello,
I have done following experiment. I take a hairdryer and insufflate hot air into plastic bottle. Then I close the bottle and put it into freezer. After couple of minutes the bottle is concave. When I open bottle then it returns to previous shape. I guess that volume of air is going down together with temperature. Question is: why does it happen? Does air fly out under pressure or fly in, because there appeared some more place?

 

[mishrashubham]

Because when the temperature decreased, the gas molecules lost heat energy, so they slowed down their movement and hence came closer to each other. This reduced the volume of the air.

 

[Dadface]

To add to the answer above when the gas cools the pressure inside the bottle drops and the greater pressure outside partially collapses the bottle.Opening the bottle allows air to move in until the pressures inside equalises with the pressure outside.

 

[pallidin]

To add to the answer above when the gas cools the pressure inside the bottle drops and the greater pressure outside partially collapses the bottle.Opening the bottle allows air to move in until the pressures inside equalises with the pressure outside.

Right, and this may or may not cause a complete re-normalization of the bottle structure.
The "may or may not" has to do with whether or not critical, non-elastic, material strain is induced during "collapse"
If so, and not uncommon, greater energy is required for a complete restitution.