Finding the Minimum Coefficient of Friction Equation

[BigMann]

stupid question because I forgot the equation

What is the equation for the minimum value of the coefficient of friction?

is it m(v^2/r) or v^2/gr

 

[physics girl phd]

check your units on them -- think about the units of the coefficient of friction -- then does one or the other make sense?

 

[BigMann]

the correct equation is v^2/gr right?

 

[physics girl phd]

well -- what are the units of that, and what are the units of the coefficient of friction?

 

[BigMann]

I know that the coefficient of friction is Newtons

 

[physics girl phd]

do you? Read about the coefficient of friction on wikipedia. Then look at the units of your proposed results.

http://en.wikipedia.org/wiki/Friction

 

[HallsofIvy]

I know that the coefficient of friction is Newtons

It's what we "know" that hurts! The Newton is a unit of force. While friction is a force, the coefficient of friction is not.

 

[BigMann]

This then means that the first equation would have to be the right one based off of the units. And if I am incorrect than I guess I just forgot it all

 

[physics girl phd]

The units of the first are mass x velocity^2/length -- kg/m^2/s^2/m -- is that the same as the units of the coefficient of friction?

Then analyze the second in the same way.

Analyzing units always helps -- but of course doesn't guarantee the right answer.

 

[BigMann]

maybe I'm not understanding the units of the coefficient of friction. Could you explain to me what they are?

 

[OlderDan]

maybe I'm not understanding the units of the coefficient of friction. Could you explain to me what they are?

The coefficient of friction is the ratio of two forces, the force of friction divided by the normal force. It has no units; it is a pure number.

As for your original question

stupid question because I forgot the equation

What is the equation for the minimum value of the coefficient of friction?

is it m(v^2/r) or v^2/gr

This does not mean much out of context. By minimum value of the coefficient of friction I assume you mean the minimum value required to achieve some condition, such as the minimum value required to keep a block from sliding down an inclined plane or to keep a car going around a curve from skidding. There is no single equation for this. It comes from figuring out how much frictional force is required to acomplish something and dividing that required force by the normal force in the problem.