FIG. 101.—The nutcracker is a lever.
The nutcracker (Fig. 101) is an illustration of a double lever of the wheelbarrow kind; the nearer the nut is to the fulcrum, the easier the cracking.
FIG. 102.—The hand exerts a small force over a long distance and draws out a nail.
Hammers (Fig. 102), tack-lifters, scissors, forceps, are important levers, and if you will notice how many different levers (fig. 103) are used by all classes of men, you will understand how valuable a machine this simple device is.
155. The Inclined Plane. A man wishes to load the 600-pound bowlder on a wagon, and proceeds to do it by means of a plank, as in Figure 93. Such an arrangement is called an inclined plane.
The advantage of an inclined plane can be seen by the following experiment. Select a smooth board 4 feet long and prop it so that the end A (Fig. 104) is 1 foot above the level of the table; the length of the incline is then 4 times as great as its height. Fasten a metal roller to a spring balance and observe its weight. Then pull the roller uniformly upward along the plank and notice what the pull is on the balance, being careful always to hold the balance parallel to the incline.
When the roller is raised along the incline, the balance registers a pull only one fourth as great as the actual weight of the roller. That is, when the roller weighs 12, a force of 3 suffices to raise it to the height A along the incline; but the smaller force must be applied throughout the entire length of the incline. In many cases, it is preferable to exert a force of 30 pounds, for example, over the distance CA than a force of 120 pounds over the shorter distance BA.
