Science Questions

Why do doors creak?

Tue, 1st May 2012

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Chitra Narayanan, Facebook asked:

Why do doors creak?


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.


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For the technically inclined, it's an example of hysteresis which shows up in a lot of dynamic situations. Geezer, Fri, 4th May 2012

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 imatfaal, Fri, 4th May 2012

I believe that is correct. The electronic "relaxation oscillator" may be another example. Geezer, Sat, 5th May 2012

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