Coefficient of Kinetic Energy; What is it and How can I calculate it?


by DBAA
Tags: coefficient, force, kinetic
DBAA
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#1
Oct30-10, 01:11 PM
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1. The problem statement, all variables and given/known data
A girl pushes a shovel at uniform velocity across a sidewalk.
The handle of the shovel is inclined at 55degrees to the horizontal
and the girl pushes the handle with a force of 100N.
What is the friction and what is the coefficient of kinetic friction.

Given Information from said Question:
For both the girl and the shovel
a= 0m/s2;uniform velocity
Fappx = 100cos55
Fappy = 100sin55

Not Given Information:
Mass, therefore gravity nor normal force can be calculated. But we don't need either as far as I know.


2. Relevant equations
Fk=Fappx (in this instance, because Fnetx is equal to 0 due to acceleration)

I don't know an equation for the coefficient of kinetic friction..

3. The attempt at a solution
I solved for force of friction; that was an easy one.
Fk=100cos55
Fk=57.36N[<--] (the direction is from my FBD assuming --> is positive)

I've never heard of "the coefficient of kinetic friction", and we definatly did not learn it in class. A quick use of google didn't give me the exact answer I needed. I then turned to wikipedia (as i love it and it's never let me down), which then told me "The coefficient of friction is an empirical measurement it has to be measured experimentally, and cannot be found through calculations."

Since i don't exist where this question takes place, and don't have her shovel or what it's made of I can't do this experimentally. So if I can't calculate it, and I can't measure it myself, how exactly do i find the coefficient of kinetic energy. What does the coefficient of kinetic energy actually mean?

Much thanks ^^
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Funkmaster W
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Oct30-10, 11:11 PM
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The coefficient of kinetic energy is the constant for which friction is acting as a retarding force to show how much force is actually being applied on the object through the equation F= mu * N where mu is the variable that stands for the coefficient of kinetic energy. there is also a shortcut that can be used when applying force on an angle to find mu which is mu = tan(theta)
PhanthomJay
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Oct30-10, 11:21 PM
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Quote Quote by Funkmaster W View Post
The coefficient of kinetic energy is the constant for which friction is acting as a retarding force to show how much force is actually being applied on the object through the equation F= mu * N where mu is the variable that stands for the coefficient of kinetic energy.
let's correct that ..it's the coefficient of kinetic friction
here is also a shortcut that can be used when applying force on an angle to find mu which is mu = tan(theta)
That does not apply here.....that applies when only the gravity component of force is acting on an incline where theta is the angle of the incline when the object just starts to move from rest as the angle of the incline is slowly increased from 0.

DBAA
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Oct30-10, 11:34 PM
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Coefficient of Kinetic Energy; What is it and How can I calculate it?


Yes, i do apologize for that confusion. the title says kinetic energy but i did mean kinetic friction.

and is the equation F=(mu)(N) the one I would still use though?
I'm not entirely sure what to plug my values in for this.
is F the friction that I found (in this question 57.36N<--)? If so, what does the N equal? Normal force (that personally doesn't make sense to me because the kinetic friction and normal force are on different axi)?
PhanthomJay
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Oct31-10, 06:42 AM
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Quote Quote by DBAA View Post
Yes, i do apologize for that confusion. the title says kinetic energy but i did mean kinetic friction.

and is the equation F=(mu)(N) the one I would still use though?
yes,for kinetic friction. (For static friction, the friction force is equal to or les than (mu)N)
I'm not entirely sure what to plug my values in for this.
is F the friction that I found (in this question 57.36N<--)? If so, what does the N equal? Normal force (that personally doesn't make sense to me because the kinetic friction and normal force are on different axis)?
The force of friction acts parallel to the 2 surface planes in contact with each other, even though the normal force acts perpendicular to it. The greater the normal force, the greater the value of the kinetic friction force, but(mu)_kinetic (or (mu)_static) is always the same for the given materials, as it is only a property of the materals of the contact surfaces, like rubber on steel has a relatively high high friction coefficient compared to say steel on teflon, etc. (mu_kinetic is generally always less than (mu)_static)). So to calculate the friction coefficient, you have to calculate the Normal force. What is the normal force? (Hint use one of Newton's laws in the y direction).


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