1. Jul 9, 2007

### rash219

1. The problem statement, all variables and given/known data

Suppose there is an object on the top of a ramp at a rest would these equation/s be correct to preform calculations considering friction applies

$$\Sigma$$F_y = n - (m * g * Cos$$\Theta$$) = 0
$$\Sigma$$F_x = (m * g * Sin$$\Theta$$) - ($$\mu$$_s * n) = 0

Suppose there is an object on the top of a ramp was sliding downwards would these equation/s be correct to preform calculations considering friction applies

$$\Sigma$$F_y = n - (m * g * Cos$$\Theta$$) = 0
$$\Sigma$$F_x = (m * g * Sin$$\Theta$$) - ($$\mu$$_s * n) = (m * a) or
$$\Sigma$$F_x = (m * g * Sin$$\Theta$$) - ($$\mu$$_k * n) = (m * a)

Note : ($$\mu$$_k * n) would be located at ($$\mu$$_s * n)

My Question is are these formulas correctly represented so that i could solve any question that involves static and kinetic friction

2. Jul 9, 2007

### Dick

Yep. That's pretty much it. Except you can't consider static friction when an object is accelerating, better put a=0 in that case, as you did the first paragraph. Good luck with actually solving problems!

3. Jul 10, 2007

### rash219

Thanks !!! Understood....

4. Jul 10, 2007

### Staff: Mentor

Careful with setting static friction equal to $\mu_s N$. That's the maximum value of static friction--the actual value may well be less.