Naked Science Forum
General Science => General Science => Topic started by: paul.fr on 25/02/2008 07:14:47
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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?
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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?
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
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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!
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Another one with dementia. It must be contagious!
Dementia, demented....welcome to my world!