# Help me understand μ!

1. Feb 9, 2012

### Ozball

1. Calculate the acceleration of a box with a mass of 5kg and μ=.5 when attached by a massless cord over frictionless pulley to a 2kg mass that is allowed to fall freely. The box is on a table, the pulley is hanging off.

2. I know a = (Fnet/total mass) but I am not sure what to do with μ! Can someone explain it to me?

2. Feb 9, 2012

### Delphi51

When you pull a sled on ice, it is easy to pull because μ is small.
When you pull it on gravel, it is hard to pull because μ is larger.
μ is the fraction of the weight that the friction force is.
Force of friction = μ*weight.
(When on a slope at an angle, you have to use the normal force - the component of the weight that pushes against the slope.)

3. Feb 9, 2012

### Ocasta

Think of mu (μ) as the magnitude of how much an object cancels out the forces trying to accelerate it.

There are two mu values for any object. The static and kinetic friction coefficients. Static is the resistance for an object to acceleration, kinetic is the resistance to acceleration after it starts moving.