Levers are said to be compounded or compound when their free ends are joined to the free ends of other levers. Large scales used in weighing luggage, bricks, wagon loads, and so on, consist of an arrangement of compound levers, whereby the arm on one side of the fulcrum is lengthened and the arm on the other side is shortened. The brake rigging on locomotives and cars is a familiar example of a compound lever.

Fig. 11.   A Lever of the Second Class.

Fig. 11. - A Lever of the Second Class.

Fig. 12.   A Nutcracker. An example of a lever of the second class.

Fig. 12. - A Nutcracker. An example of a lever of the second class.

Fig. 13.   A Safety Valve. A lever of the third class.

Fig. 13. - A Safety Valve. A lever of the third class.

Two or more levers joined and working together (Fig. 14) illustrate this principle of leverage. Here a weight suspended on a hook at W causes the end of the second lever P to swing downward.