# Acceleration and coefficients of friction

1. Dec 12, 2011

### nic.harv

how would you find the rate of acceleration when given the force, mass, and the coefficient of friction?? what would the formula(s) be??

i am so confused! HELP!

2. Dec 12, 2011

### JHamm

You'll need to give some more information about your problem, taking a stab at it I'll assume you have a block of mass $m$ sitting on a surface with coefficient of kinetic friction $\mu$ and there is a force $F$ acting on the block parallel to the surface it rests on.
In that case the force of friction becomes
$$F_{friction} = mg\mu$$
With $g$ being the acceleration due to gravity. Then from Newton's second law
$$F_{net} = F_{friction} - F$$
The minus sign is because friction will act in the opposite direction to the motion of the block. From this you know that
$$Acceleration_{net} = \frac{F_{friction} - F}{m}$$

3. Dec 12, 2011

### Lsos

Force = Mass x Acceleration

You already have the force and the mass, the math is very easy to find the acceleration.

Friction complicated it just a little, as friction is a force acting opposite of the direction of acceleration. So the "Force" in the above formula is actually "Force - Friction". As JHamm explained, the formula for "Friction" is probably Friction = Mass x 9.81 x coefficient of friction.

Basically the exact same thing as JHamm said, but hopefully if two people say it, it will make more sense...