Why do doors creak?

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Offline thedoc

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Why do doors creak?
« on: 01/05/2012 16:56:12 »
Why do doors creak?
Asked by Chitra Narayanan, Facebook


                                        Visit the webpage for the podcast in which this question is answered.

 

« Last Edit: 01/05/2012 16:56:12 by _system »

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Offline thedoc

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Why do doors creak?
« Reply #1 on: 01/05/2012 16:56:12 »
We answered this question on the show...



Dave -   If you have a door which is getting a bit old, getting a bit rusty and you haven’t oiled it properly, you get a very similar thing to brakes squealing or in fact, dragging finger nails down a blackboard.  It’s to do with stick and slip.  What happens is that you get quite a lot of friction and there's a lot more friction when two things are stationary than when they're moving.  So, essentially the two bits of the hinge lock together, then the hinge bends a bit, and then the force gets enough for it to break, and it jumps forward a bit and then it stops, and then it bends a bit, and it jumps forward…
This jumping can happen at a range of pitches, including the horrible 50-100 Hertz range.  As you’re getting jump, jump, jump, jump, what you hear is this horrible creak noise.
« Last Edit: 01/05/2012 16:56:12 by _system »

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Offline Geezer

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Re: Why do doors creak?
« Reply #2 on: 04/05/2012 02:24:41 »
For the technically inclined, it's an example of hysteresis which shows up in a lot of dynamic situations.
There ain'ta no sanity clause, and there ain'ta no centrifugal force æther.

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Offline imatfaal

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Re: Why do doors creak?
« Reply #3 on: 04/05/2012 09:49:58 »
Slip-stick is the mechanism for making annoying noises by running your finger around the rim of a wineglass I believe.  I presume that stringed instruments (arco) also work like this
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Offline Geezer

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Re: Why do doors creak?
« Reply #4 on: 05/05/2012 06:20:52 »
Slip-stick is the mechanism for making annoying noises by running your finger around the rim of a wineglass I believe.  I presume that stringed instruments (arco) also work like this

I believe that is correct. The electronic "relaxation oscillator" may be another example.
There ain'ta no sanity clause, and there ain'ta no centrifugal force æther.