Although people don’t notice it, we use the wheel and axle in our everyday lives.  Cars have this simple contraption inside the hood as well as the wheels, and the very popular bicycle mainly consists of two wheel and axles.  The wheel and axle is one of the six simple machines, and has three main uses, to transport things, to make something easier to lift, and as a gear.  The mechanics of a wheel are very simple.  If the axle turns one revolution, then the wheel turns one revolution.  To transport things with the wheel and axle, the axle is turned so that the wheels will turn and move the object.  The other two uses involve the concept of mechanical advantage.  Each the wheel and the axle have a radius.  For each revolution of the axle’s radius the wheel’s radius is turned the same number of times.  Say the axle’s radius is one inch, and the wheel’s radius is three inches.  The mechanical advantage of that situation is three.  For all the energy you use to turn the axle, that effort is tripled with the wheel.  Because of this, cars can be driven easier, and things can be pulled easier.  Gears are wheels with teeth in them.  There is also a mechanical advantage with gears.  If a gear with three teeth turns a gear with nine gears the mechanical advantage is three.  You us effort to move the small gear, and it moves the big gear, tripling your effort.