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Finding force of friction 
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#1
Nov2310, 08:06 PM

P: 38

1. The problem statement, all variables and given/known data
I have a lab project in physics and I'm having a bit of trouble. We measured the Applied force of a moving block of wood using a spring scale. The first trials were don't with just the table , knowing the mass and applied force I was able to find the friction force; simply it was the same as F app. My problem now is that we did other trials on sandpaper, and I have the Applied force and mass and I don't know how to find the mass. We are suppose to find the Co efficent of friction, but not through math ; we have to use a graph where : y = mx aka Ff=U*Fn Which isn't too bad, I just can't figure out how to get Force friction with only the mass and applied force when it is using the sand paper. Mass = 0.27952 kg Force applied = 2.0N Fn = Fg mg= 0.27952(9.8)= 2.739296 N Help please 2. Relevant equations 3. The attempt at a solution 


#2
Nov2310, 09:14 PM

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P: 6,036

I am assuming that the block or mass is moving slowly or at constant speed when the force is applied...in the 2nd example, you know the applied force so you then know the kinetic friction force, and since you have calculated the normal force, plot that point on the graph with Ffriction on the y axis and the normal force on the x axis. Then try another mass, and do the same, moving it slowly; and yet another....your graph should approximate a straight line, the slope of which is____?



#3
Nov2310, 09:44 PM

P: 38

Can't find friction, yes I have the Force normal , but no coefficient. Even if I know the applied force I don't know how that helps me find friction example
FappFfrict = MA I only know F app and mass Ffrict = U * Fn Don't see how you solve unless Fapp in the 2nd problem also equals Ffrict. 


#4
Nov2310, 10:14 PM

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P: 6,036

Finding force of friction



#5
Nov2310, 11:05 PM

P: 38

Oh true, didn't even think about it. Ha.
Thank you , appreciate it. 


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