We know that the frictional force always opposes the relative motion. Recently, I happened to read somewhere that "It is the frictional force which causes a car to accelerate on road". My question is
a) How can the frictional force cause "the car to move forward"? According to the law, the friction always opposes the relative motion, and suppose the relative motion of the car is in the forward direction with respect to the road, so the friction must act in an opposite direction (that is backwards) and not help "the car to move forward". Or am I getting wrong somewhere?
b) The car pushes the ground backward which in turn pushes the car forward. This particular reaction force should have helped in the motion of the car. Shouldn't it be the this reaction force responsible for the car's motion and not the frictional force(since the friction will in an opposite direction to the relative motion)?