At the moment that the front wheels are turned, the car possesses velocity in a straight line v , which may be resolved in two directions x and y at right angles to one another (fig). The wheels should simultaneously roll along x and slip along y. But if slipping ought to take place, then the force of friction always comes into play, acting in the opposite direction to that in which slipping should take place. This external force F is what causes the whole car to turn the way required.