Whats the diffrence between these two equations for acceleration in the x direction?

Question

I have two formuals for the same thing and I have no idea which one is for what.

a_x = -μ(g)

a_x = g/μ_s

Is one for static friction and the other for kinetic?

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Answer 1

Not knowing the full background of your question, but:

1. By definition, the coefficient of friction µ is always less than 1. Acceleration from the weight of the mass of an object under friction, e.g. down a ramp, is less than the maximum, which is full acceleration of gravity (g), so only the first equation makes any sense. I can not imagine where the second equation comes from, since g/µ would be greater than g!
2. Also, you state acceleration in x-direction, a_x. but x is usually defined as horizontal, while g acts vertically, in the y-direction.

Let me know if you want to discuss ...