AP Physics B help

<p>I'm working through review materials and I'm completely dumbed out by the Seahawks loss -_-;</p>

<p>If a sphere is at the top of an incline, what is the minimum coefficient of friction necessary to make it roll as opposed to just slide down?</p>

<p>There are no values so the answer is supposed to be terms like h=height L=length of ramp, etc</p>