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.