# How is the average force of friction calculated?

Aug 12, 2018

For static frictional force it increases linearly w.r.t applied force ,so by taking the mean of the maximum value of friction with the minimum value you can get the average force of friction.

Suppose,a mass of $m$ was lying on a horizontal surface whose frictional coefficient is $\mu$.

So,maximum static frictional force that can act will be
$\mu N = \mu m g$

So,on increasing externally applied force upto $\mu m g$ amount,static frictional force will also increase linearly.

So,maximum value of static friction is $\mu m g$

And minimum value is $0$ that is when no external force is applied.

So,average static frictional force in this case will be $\frac{\mu m g + 0}{2} = \frac{\mu m g}{2}$

But,after it has started moving,kinetic frictional force comes to act and its value is always constant.