Man's Way of Helping Himself
Out of the few simple machines mentioned in the preceding Sections has developed the complex machinery of to-day. By a combination of screw and lever, for example, we obtain the advantage due to each device, and some compound machines have been made which combine all the various kinds of simple machines, and in this way multiply their mechanical advantage many fold.
A relatively simple complex machine called the crane maybe seen almost any day on the street, or wherever heavy weights are being lifted. It is clear that a force applied to turn wheel 1 causes a slower rotation of wheel 3, and a still slower rotation of wheel 4, but as 4 rotates it winds up a chain and slowly raises Q
. A very complex machine is that seen in Figure .
FIG. - A simple derrick for raising weights.
FIG. - A traveling crane.
FIG. - A farm engine putting in a crop.