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.

 

[PJC01]

Hello,
Thank you for sharing your experiment with us. It seems like you have observed an interesting phenomenon with the plastic bottle and the changes in air pressure. From your description, it appears that the hot air inside the bottle cools down and decreases in volume, causing the bottle to become concave. When you open the bottle, the air inside expands again and returns the bottle to its original shape.

The reason for this is due to the ideal gas law, which states that the volume of a gas is inversely proportional to its pressure at a constant temperature. In other words, as the temperature of the air inside the bottle decreases, its volume also decreases, causing a decrease in pressure. This decrease in pressure is what causes the bottle to become concave.

As for your question about whether the air flies out or in, it is actually both. As the air inside the bottle cools down, it contracts and some of it may escape through the opening. At the same time, the decrease in pressure outside the bottle causes air to rush in to equalize the pressure.

Overall, your experiment demonstrates the relationship between temperature, volume, and pressure in gases. It is a great way to observe and understand the principles of the ideal gas law. Keep experimenting and asking questions!