A uniform ladder leans safely against a vertical wall at an angle 45° to the horizontal ground. The wall is 100% slippery, while at the ground the coefficient of friction is µ . Prove that since the ladder is not falling, µ [itex]\geq[/itex] 0.5 I've attempted to solve this, and think I have, granted that Friction=[itex]\mu[/itex]mg, but is this true? If so, is it always true? I was taught that Friction=[itex]\mu[/itex]*Normal Force, and normal force=mg, but there are 2 normal forces in this problem, that of the wall on the ladder and that of the ground on the ladder.