# Friction Formulas

1. Mar 20, 2009

### Lobber

1. The problem statement, all variables and given/known data
What is the formula for: Fn, Ff, and mu when you have a object sliding down a ramp.
Variable know are D, T, A, Vi, and the angle of the ramp above the horrizon.

3. The attempt at a solution
I've tried a few that ended up being quite long and all wrong...

2. Mar 20, 2009

### Vuldoraq

What are D, T, A? I take it Fn is the normal force, Ff is the friction force and Vi is the initial velocity?

You should obtain expressions involving trig. functions and the properties of your mass.

3. Mar 20, 2009

### Lobber

D=1.83M
T=1.06S
A=3.257m/s/s
angle/theta is 54 degrees
Vi=0
M=0.5kg
Friction force?
Normal force?
Mu?

Formula#1 (didn't work...)
Ff:
(cos theta A)*M=Max=Fx
Fx=Ffx-Fgx
Fgx=(sin theta)Mg.
Fn:
Ma(sin theta) = May
May=Fy=Fny-Fgy
Fgy=M*(cos theta)g

Ff/Fn=mu

Formula2

Fx=Max
ax=a(cos theta)
Fy=May
ay=a(sin theta)
Fg=Mg
Fx=Max=Fgx-Ffx
Fgx=Mg(sin theta)
Fy=May=Fgy-Fny
Fgy=Mg(cos theta)
Ff/Fn=mu.

My answers with these two formulas were ff=4.93 Fn=4.20 mu=1.20

for formula 2 they were Ff=3 Fn=1.56 mu=1.92

4. Mar 20, 2009

### Lobber

I think I might have fixed my problem as ay=Fgy=0 so that changes things. Also it's an inclined plane question.

Last edited: Mar 20, 2009
5. Mar 20, 2009

### Vuldoraq

Your value of mu should always be less than one.

I think you need to find the difference between the actual force at the bottom and the theoretical force at the bottom.

Please could you post equations that would give the component of weight normal to the surface and the component of wieght parallel to the surface and we will go from there.

Edit: don't split it up into x and y parts, it makes things more messy.

Last edited: Mar 20, 2009