A wheel-and-axle moves vehicles forward when force is applied to the simple machine through gears or a driveshaft. A steering column connected to the steering wheel turns the wheels on a car's front wheel-and-axle assembly.
Fundamentally, a wheel-and-axle turns on its axis. The axle has a smaller radius than the wheel.
A wheel-and-axle is a complex lever system, with the center of the wheel-and-axle serving as the fulcum. The radii of the two parts are the arms of a lever. A lever is more efficient than a wheel-and-axle because a lever does not need to overcome the force of friction. Friction exists between the wheel and the ground and between the axle and the gears.