Why does chalk make a squeaking noise on a blackboard?

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paul.fr

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When writing on a black board, why does the chalk make that awful squeaking noise? And why should the angle and whether you push or pull the chalk make a difference?
« Last Edit: 04/03/2008 23:26:50 by chris »

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Offline lightarrow

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Re: Why does chalk make a squeaking noise on a blackboard?
« Reply #1 on: 25/02/2008 13:12:19 »
When writing on a black board, why does the chalk make that awful squeaking noise? And why should the angle and whether you push or pull the chalk make a difference?
I'm almost sure there has already been a thread about it sometimes ago.
The reason is chalk friction with the board: the chalk accelerates fast, then stops then accelerates again, many times every second, making it vibrate at high frequency. So, angle, push, but also chalk lenght , affect the kind of sound (or not sound).

Found that thread. Guess who asked that question?  [:)]
http://www.thenakedscientists.com/forum/index.php?topic=9332.0
« Last Edit: 25/02/2008 13:15:03 by lightarrow »

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Offline DoctorBeaver

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Re: Why does chalk make a squeaking noise on a blackboard?
« Reply #2 on: 25/02/2008 15:24:19 »
Found that thread. Guess who asked that question?  [:)]
http://www.thenakedscientists.com/forum/index.php?topic=9332.0

Another one with dementia. It must be contagious!
Fledgling science site at http://www.sciencefile.org/SF/content/view/54/98/ needs members and original articles. If you can help, please join.

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paul.fr

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Re: Why does chalk make a squeaking noise on a blackboard?
« Reply #3 on: 27/02/2008 09:39:44 »


Another one with dementia. It must be contagious!

Dementia, demented....welcome to my world!