Why Do Doors Slam?

[Bert]

Why is it that on the calmest of days, when there isn't even a breeze, that, if you leave the front door and back door of your house open, one of the doors in between will slam shut with enough force to wake the dead?
The fact that there is no breeze would indicate that there are no great differences of air pressure anywhere, certainly not over the distance between my front door and the back door.

[Canary42]

Poltergeist

[nungate]

Doors slam in our house because someone has usually p*ssed me off!

[joggerjayne]

Prank by a neighbour?

[Old_Geezer]

Because they can.

[DaisyNonna]

People slam doors.

[jno]

do you mean the slamming door is literally in between front and back? I have only a straight corridor between mine, but if both doors are open one will slam. But there's always a detectable airflow coming in through one or the other.

[Answerprancer]

According to my Grannie, it's "Archiebald McFee".

[Mamyalynne]

http://www.amazon.co.uk/Door-wedges-rubber-set-2/dp/B001LBCB04

[jim360]

I typed in "closed door slam open door" in to google and found this paper:

https://physics.le.ac.uk/journals/index.php/pst/article/viewArticle/469

The English needs some tidying up, and perhaps the Science is a bit too heavy for most, but in summary:

When a house is effectively airtight, pressure differences in front of and behind the door are balanced by air flowing around the door. As the door closes, there's less room for the air to flow but the pressure must still be equalised. The air is finding it harder to fit through the small gap, so more work is going into displacing that air, and the door moves slowly.

Open a window or door in the house somewhere, though, then air outside the house comes into play. Either:

i) the window is open behind the closing door -- air flows from outside to equalise the pressure, or;

ii) the window is open in front of the closing door, in which case as the door closes air can escape from the higher pressure area through the window.

In both cases air resistance no longer slows the door down, so that as it closes finally it does so at "full speed". If there is a drat then the door can even speed up and slam harder than ever.

[jim360]

drat = draught*.

[mibn2cweus]

The whole side of the house facing the smallest breeze is an obstruction to air flow creating a pressure differential between front and back, focusing it to the one available passage through the obstruction . . . the hallway.

[cupid04]

Do you live near an army firing range? That can cause doors to slam amongst other things!

[ST24]

Any kind of change in pressure can cause it ; could be a sudden change in barometric pressure or a change of temperature in your roof space which causes expansion or contraction of air.

[TheOtherHalf]

perhaps theres a bit more breeze at the front of house than back. It is with ours anyway, even though you cant feel it when youre out there. Thus when both doors are open, the front wind blows through the house.

[vascop]

I also remember resding somewhere that whwn a door is left ajar (almost closed), that the air flow through the gap works like air flow over the wings of a plane, and causes a difference of pressure on each side of the door and causes it to slam.

[jomifl]

Even on what seems to be a very calm day localised gusts occur. They can be caused by turbulence between layers of air of differing densities moving at different relative speeds or by 'bubbles' of warm air heated by the sun warmed ground breking away from the ground to form 'thermals'. These are more noticeable at sea when on flat calm days a glassy sea surface is disturbed by these gusts to form 'cat's paws'.

[Bert]

I had a look at the link provided by jim360 and found this in the abstract: "This paper presents a model for this phenomena" Aaargh! This error is repeated twice in the first paragraph. But the paper is actually dealing with the observation that it is easier to close a door in a room with an open window that in one with no openings, which I thought had a pretty obvious solution, which the authors come to eventually. Thanks for the serious answers. Logic says that there must be a difference in pressure between the front door and the back door, even if I cannot detect it with my wet forefinger. But I still find it hard to believe that the difference in pressure is enough to move a door with such force that it slams.

[jim360]

Well yes the paper has bad grammar, and it's maddening, but it still deals with your question. Up to simplifications, it does show that the pressure can make a huge difference, because without an open window the door has to do the work of equalising the pressure, and when a door or window is open then that can allow the pressure to be equalised and the door need not lose speed when closing.

You see it al the time, that doors slam on the tiniest changes in pressure -- so why should it be so hard to believe?

[vascop]

Don't forget that Force=Pressure x Area, so a small increase in pressure over a large area (door) can produce quite a big change in the force.