As you probably know, there are 6 simple machines:
In the nineteenth century, the German mechanical engineer Franz Reuleaux (1829 – 1905) postulated that the 6 simple machines could be placed into 2 groups:
Ⅰ) the lever, the pulley and the wheel and axle
The “lever family” is grouped together because they function around a central point:
the fulcrum, the pulley axis and the axle.
Ⅱ) the inclined plane, the wedge and the screw
The “inclined plane family” is grouped together because they function using angles.
A simple machine is something that can change the direction of a force, change the magnitude (amount) of a force or both.
In a simple machine, effort is the unchanged force (or input force) and load is the changed force (or output force).
When a simple machine changes the magnitude of a force, you are gaining what is known as a mechanical advantage, which equals the output force divided by the input force.
So, for example, if you are pressing fifty pounds on a lever to move a 200 pound boulder you have a mechanical advantage of 4. (200 ÷ 50 = 4)
You do get 200 pounds of force by only exerting 50 pounds of force, but moving the boulder ¼ of a foot (3 inches), requires moving the lever one foot.
Still, even though the lever doesn’t give you something for nothing, it does make moving the boulder possible.