What do you know about the coefficient of friction?
Difficulty: Easy
Coefficient of friction (µ):
The ratio between the force of limiting friction Fs and the normal reaction R is constant. This constant is called the coefficient of friction and is represented by µ
Thus $\mu=\frac{Fs}{R}$ ......(i)
Or $Fs = \mu\:R$ ......(ii)
If m be the mass of the block, then for horizontal surface,
R = mg .......(iii)
Hence $Fs = \mu\:mg$ ........(iv)