I can understand that friction is responsible for the acceleration of a car. As the tires turn they push back on the road and the horizontal component of the contact force(ie friction) opposes the motion of the tires and push in the forward direction, making the car move. 1) Which type of friction are we talking about here? Since we are talking about the tires, is it rolling friction that helps to accelerate the car? 2) Constant velocity Suppose we are keeping the car going at a constant velocity. The net force should be zero. Does that mean the frictional force is balanced by something? 3) Brakes My teacher told me friction plays a very important role int he working of breaks. I'm confused. Friction is supposed to keep the car accelerating , so how does it help in stopping it then? 4) Proper inflation of tires saves fuel: I am unable to arrive at a reason for this. Again I am not sure if this is done to reduce friction or increase friction. I keep thinking it has to increase friction as friction is what helps the car to move. But the whole thing is very counter intuitive. I am really confused. Please do help me clear this up.