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In Reply to: RE: Your personal experience notwithstanding,... posted by Tre' on August 25, 2016 at 14:01:34
compared to the contact area the the groove is not that much rougher than the flat surface. so the coefficient of friction aka mu is probably the same within a tiny fraction. the whole idea with this constant is that it ignores the shape of the contact areas. you do not need to know that the contact surface is 10 sqrt micron or 10 sqrt feet. you know the vertical force, multiply it by mu and you got the kinetic friction force. There is a minuscule difference in forces when one has to accelerate the moving mass of the stylus assembly around the modulation but that is negligible compared to the kinetic friction. Newtonian physics is very well modeled :)
decided to add this tidbit.....
The force due to friction is generally independent of the contact area between the two surfaces. This means that even if you have two heavy objects of the same mass, where one is half as long and twice as high as the other one, they still experience the same frictional force when you drag them over the ground. This makes sense, because if the area of contact doubles, you may think that you should get twice as much friction. But when you double the length of an object, you halve the force on each square centimeter, because less weight is above it to push down. Note that this relationship breaks down when the surface area gets too small, since then the coefficient of friction increases because the object may begin to dig into the surface. If that happens when you are in the groove of a record you have bigger problems than the skating force.
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
Edits: 08/25/16 08/25/16Follow Ups:
Penguin,
Thanks for posting this video. I'm frustrated by my inability to do the math even at this basic level, but I was able to follow it in this case and learned a lot.
Doug
"Note that this relationship breaks down when the surface area gets too small, since then the coefficient of friction increases because the object may begin to dig into the surface. If that happens when you are in the groove of a record you have bigger problems than the skating force."
The tip of the stylus is not meant to come into contact with the vinyl so "digging in" might just happen with the tip riding a flat surface. But, as has already been said, the shape of different styli will be different so it (the flat surface method of adjusting AS) is still a crap shoot.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
if no scratch on the smooth part, then everything else is the same as in the groove. So the kinetic friction force is closely equal. everything else is negligible.You are grasping your straws :)
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
Edits: 08/25/16
I was pointing out what Peter has already said.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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