Question

if normal force is doubled what happens to friction

Answer 1

If the normal is multiplied there will be no adjustment in coefficient of friction, as it just relies on the idea of a couple of the surface in contact. So multiplying the normal will simply twofold the frictional power and won't influence the coefficient of friction. 
On the off chance that normal force is multiplied the coefficient of the kinematic friction of a body additionally bent over to the movement going to begin. 
Be that as it may, once after the movement is begun and keeps on moving, the kinetic friction diminishes as force doubles. 
That implies the coefficient of friction has diverse values while in stationary or in the movement state.

Answer 2

Answer:    IF NORMAL FORCE IS DOUBLED. THEN FRICTIONAL FORCE       ALSO GETS DOUBLED.

Explanation:

As you know that  friction (limiting friction)  ∝ normal force (N)

i.e f ∝  N

⇒ f1/f2  = N1/N2 --------------------eq.1

here f1 = f1                   N1 = N1

        f2 = ?                   N2 = 2N1

from 1 , f2 = f1 × (N2 / N1)

         ⇒    f2 = f1 × (2N1 / N1)

therefore f2 = 2f1

therefore if normal force is doubled then frictional force is also doubled.