A force creates a pressure differential without a container

You can use a force to make air pressure without the walls of a container.
Uranium enrichment uses uranium hexafluoride UF6 in a gas centrifuge.
“UF6 gas is placed in a gas centrifuge cylinder and rotated at a high speed. This rotation creates a strong centrifugal force so that the heavier gas molecules (UF6 containing U238 atoms) move towards the outside of the cylinder.”