How is the average force of friction calculated?
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
So,maximum static frictional force that can act will be
So,on increasing externally applied force upto
So,maximum value of static friction is
And minimum value is
So,average static frictional force in this case will be
But,after it has started moving,kinetic frictional force comes to act and its value is always constant.