Why do doors close easier with a window open?
In: Physics
When the door gets close to closing, there’s just a narrow gap for all of that air caught by the door to escape through, which is why it often stops just before closing. With a window open, the air has another path to escape out of the room rather than that tiny gap.
Air pressure. When you close the door you’re pushing more air into the room than can fit. Most of it escapes through the gap at the bottom or other places, but it provides resistance.
When the window is open, the pressure can’t build up, as it has an easy escape path.
This has to do with the amount of air contained within the room. Whenever a door is closed some amount of air is moved.
If the door is closed from the outside, it slightly increases the amount of air in the room. Now, this air will have a direct path to escape through an open window, making the door close easily. Otherwise, one can feel this slight change in pressure while closing the door.
Similarly, if the door is closed from the inside, it slightly decreases the amount of air in the room. Now, the required air to maintain the same pressure will have an easier path to enter through an open window, making the door close comfortably.
It’s the wind. Even if you don’t feel it strongly, air is coming in through the window. Most doors are meant to be moved around very easily. Even a tiny push can move a lightweight door on smooth hinges. If the window is across the room from the door, than the farther the door closes, the more of its surface area is facing the open window, and it closes even faster than before. The doors in my home will slam shut if the window is open even when it isn’t windy.
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