Aerodynamic drag

The resistance of the air to forward movement, sometimes called "air resistance". This is a factor of the shape of the vehicle (drag coefficient and frontal area), the objects which stick out (i.e., mirrors, mufflers, bumpers), the amount of turbulence at the rear of the vehicle, the nature of the vehicle's skin surface, and the amount of air going through the vehicle for cooling and ventilation. The faster you go, the greater the air friction (air friction = velocity x velocity). The faster you go, the greater the amount of power needed to overcome this drag (power = velocity x velocity x velocity).