Why is the difference in air pressure able to move things? (Ex. Close a door)


Why is the difference in air pressure able to move things? (Ex. Close a door)


ELI5 pressure is force applied to an area. So if I have high air pressure on one side of a door and low pressure on the other side, the side with lower pressure will apply less force to the door than the higher pressure side as such the net force will push the door towards the low pressure side just as if you and a friend are each tugging on a rope, the person that is tugging “harder” will pull the rope towards them.

If you have pressure on one side of a door, the force on the door is the pressure times the area of the door. Doors are pretty big, so a small pressure can result in a large force. If you have a different pressure on each side, even different by a little bit, times the area of the door it can produce enough force to swing the door.

If you replaced all the air in room with foam balls, it would be plainly obvious why it can move a door. One foam ball pushes on another and another and another.

If there is high air pressure on one side, the air molecules keep bumping into each other and getting pushed towards the side. The side includes the door. If the air pressure is constant on both sides, the door stays in place as the force inwards is the same as the force outwards. If one force is lower, the door moves.

Think of it as two people pushing on a door. The door wont move. But if one person pushes with less force, the door moves

Imagine there is no air in two rooms connected by one, open door. Say for the sake of this exercise you don’t need air, and are standing behind the open door. You blow wind from your lungs onto the door and it closes. Air pressure is actually a term referring to the speed and inertia and air that pressures things. A little bit of air pressure does nothing, as closing a door would likely take multiple deep breaths of air. But the sky is big and has more than a few lungfuls of air in it, so generally a door closing isn’t the most surprising thing.