Final answer:
If the pressure of the gas in a sealed container is lower than the outside air pressure, the external pressure can compress or collapse the container. This is particularly apparent with non-rigid containers or when the internal gas cools, causing the container to contract under atmospheric pressure.
Step-by-step explanation:
If the pressure of the gas inside a sealed container is lower than the outside air pressure, the external atmospheric pressure will exert a greater force on the outside walls of the container than the gas does on the inside walls. This can result in the container being compressed or even collapsing if the material is not rigid enough.
For example, in the case of a hot-air balloon, when the pressure of the gas inside the balloon is lower than the atmospheric pressure outside, the balloon would not be able to inflate. Similarly, when a rigid container with gas inside is exposed to lower temperatures, the pressure of the gas decreases, and the external atmospheric pressure may force the container to contract, as demonstrated in the experiment with the syringe filled with hot steam being cooled.