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If you consider a basically uniform massive door (say, 300 N) where there is some coefficient $\mu_{s,k}$ of static and kinetic friction between the thing on the inside of the door, and where the door is 1 meter long (1 meter from pivot point to end of door), is it reasonable that differences in air pressures inside and outside of the room could cause the door to open slightly, seemingly by itself, if it started where the metal thing was not snugly in the hole?

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You have also to consider how well the door is vertically oriented. Even if it is slightly off vertical gravity can open it, in my experience. There are badly hung doors that always open unless latched. –  anna v Oct 28 '12 at 4:18
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Yes, provided the air pressure change is rapid enough (simple air pressure changes due to weather won't do). It happens if the rooms has closed windows, two doors, and the room is fairly small: you slam one of them, and the other closes (or opens). It happens all the time in my bathroom.

An explosion would do as well.

If the door connects a hall and a room, the hall is narrow and the door is light, someone running in the hall could produce enough air pressure to open the door, too.

I find it unlikely that it could be triggered by temperature differences between two rooms (provided the temperature difference is not increased abruptly), because even though temperatures were different air pressure should be roughly the same for the aforementioned reasons.

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Weather also works. My room door keeps shutting itself in windy weather if windows are open. –  b_jonas Oct 28 '12 at 11:59
Wind definitely works. I was not clear enough. What I meant is that if you close the door and air pressure increases over a few hours the door won't open by itself as a result of it. The door is not airtight, therefore air will slowly flow through it keeping air pressure roughly constant troughout the house, provided there is no wind or other similar phenomena (explosions, doors shut violently, etc.) running around the house (remember Bernoulli's law). –  Ferdinando Randisi Oct 28 '12 at 13:47
@FerdinandoRandisi, no windows were opened, and no violent reactions were occuring that resulted in lots of wind. The only thing is that I do not have my AC on in the room (which is rather large in volume) whereas outside the room there is constant AC... –  tacos_tacos_tacos Oct 28 '12 at 16:26
It seems that your question is more oriented to explain a particular event, rather than speculating on the theoretical possibilities of this event to happen, as I first thought. Then my best suggestion would be to see if it happens again reproducing all the conditions that led it to happen the first time: do it at the same time of the day, with AC set at the same temperature, with the same people in the same positions around the house, with same lighting, etc., and see what happens. –  Ferdinando Randisi Oct 29 '12 at 10:20
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There are two ways a door can open slightly by itself. One is as you mentioned air flow and air pressure, and the other is if the hinges are not exactly vertical and/or aligned properly. Especially since the wooden frames move with time and the hinge screws tend to loosen doors may be come more and more likely to not have their most stable position as closed.

As far as the air pressure goes, think about it this way. While the door is closed, pressure builds until it is relieved by the door opening, or the air flows out from somewhere else (windows cracks). So the total pressure than can be reached depends on the configuration.

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