I read an article where the author tried to find the maximal speed a car can have when taking a turn of certain radius. They represented the car as a point and claimed that the force of friction is the centripetal force - acting perpendicular to the trajectory of the car. I do understand why friction is the force that propels the car. What I don't understand is: Why is the net force acting on a car perpendicular to its trajectory? I have drawn this diagram: The rectangle is the car. The green segments are the wheels. What is wrong with my diagram?