Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 01/05/2012 16:56:12
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Why do doors creak?
Asked by Chitra Narayanan, Facebook
Visit the webpage for the podcast in which this question is answered. (http://www.thenakedscientists.com/HTML/podcasts/show/2386/)
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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.
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For the technically inclined, it's an example of hysteresis which shows up in a lot of dynamic situations.
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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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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.