A nutcracker consists of a pair of levers of the second order. The fulcrum is at one end and the effort or pressure is applied at the opposite end of the levers or handles, while the equivalent of the weight (in this case the nut) is placed between the effort and the fulcrum. Again the _effort arm_ is measured from the fulcrum or hinge pin of the tool to the point where the hand pressure is applied, and the weight arm is measured from the fulcrum to the nut. The effort arm may be four or five times as long as the weight arm, so that the pressure exerted on the nut is four or five times as great as that exerted by the hand on the ends of the handles. [Illustration: FIG. 2.--AN ANGULAR OR BELL-CRANK LEVER] In the case of a pair of sugar tongs we have another tool something like the nutcracker in construction, but here the weight, i.e., the lump of sugar, is seized by the ends of the tongs while the hand pressure is applied somewhere between the fulcrum and the weight. Hence we have here a lever or pair of levers of the third order. The _effort arm_ of a pair of tongs is always shorter than the _weight arm_ and the pressure on the sugar lump is always less than that exerted on the tongs by the hand. Evidently the most powerful tool of the three is the nutcracker, because the effort arms extend over the full length of the tool and are always longer than the weight arms. A lever need not consist of a straight bar; the effort arm may form an angle with the weight arm, forming what is known as an angular or bell-crank lever (Figure 2). When a common claw hammer is used to pull out a nail, the claws that slip under the head of the nail form the weight arm and the hammer handle the effort arm. A horizontal pull on the handle produces a vertical lift on the nail. Sometimes two or more levers are interconnected, as in Figure 3, the effort arm of one being linked to the weight arm of the other. This serves to increase the lifting force at the weight and at the same time keep the mechanism within compact limits. Such compounding can go on indefinitely and is subject to all sorts of variations. [Illustration: FIG. 3.--COMPOUND LEVERAGE] One thing we must not forget, and it is a matter that is commonly overlooked by perpetual motion cranks, namely, that while a pound of pressure on the effort arm may be made to lift two, four, or a hundred times as many pounds on the weight arm by varying the relative length of these arms, it has to move two, four, or a hundred times as far as the weight arm, so that the work done on one side of the fulcrum is always exactly equal to that done on the other side. CONTINUOUS REVOLVING LEVERAGE [Illustration: FIG. 4.--PRIMITIVE GEAR WHEELS--TWO COACTING GROUPS OF LEVERS]