Naked Science Forum

General Science => General Science => Topic started by: paul.fr on 25/02/2008 07:14:47

Title: Why does chalk make a squeaking noise on a blackboard?
Post by: paul.fr on 25/02/2008 07:14:47

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?

Title: Re: Why does chalk make a squeaking noise on a blackboard?
Post by: lightarrow on 25/02/2008 13:12:19

Quote from: paul.fr on 25/02/2008 07:14:47

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

Title: Re: Why does chalk make a squeaking noise on a blackboard?
Post by: DoctorBeaver on 25/02/2008 15:24:19

Quote from: lightarrow on 25/02/2008 13:12:19

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!

Title: Re: Why does chalk make a squeaking noise on a blackboard?
Post by: paul.fr on 27/02/2008 09:39:44

Quote from: DoctorBeaver on 25/02/2008 15:24:19

Another one with dementia. It must be contagious!

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