Lever
The lever is the simplest of all machines, and is only a straight bar of iron, wood, or other material, supported on and movable round a prop called the fulcrum, and having the weight to be moved and the power to move it applied at two other points. The law is that the power and weight are in the inverse ratio of their distances from the fulcrum. This is equally true for straight or bent levers, and holds good whatever be the relative positions of the power, weight, and fulcrum; and as there can be three different arrangements of these, we thus obtain what are called the three kinds of levers. The first kind is where the fulcrum is placed between the power and the weight; levers of the second kind are those in which the weight is betwixt the power and the fulcrum; in levers of the third kind the power is betwixt the weight and the fulcrum. To produce equilibrium in levers of the first kind, the power may, according to the ratio of the lengths of the arm, be either greater or less than the weight: in the second kind it must always be less, and in the third kind always greater.