The Wheelbarrow as a Lever
Man's Way of Helping Himself
The principle of the lever is always the same; but the relative position of the important points may vary. For example, the fulcrum is sometimes at one end, the force at the opposite end, and the weight to be lifted between them.
Suspend a stick with a hole at its center as in Figure, and hang a 4-pound weight at a distance of 1 foot from the fulcrum, supporting the load by means of a spring balance 2 feet from the fulcrum. The pointer on the spring balance shows that the force required to balance the 4-pound load is but 2 pounds.
The force is 2 feet from the fulcrum, and the weight (4) is 1 foot from the fulcrum, so that
Force × distance = Weight × distance,
or 2 × 2 = 4 × 1.
Move the 4-pound weight so that it is very near the fulcrum, say but 6 inches from it; then the spring balance registers a force only one fourth as great as the weight which it suspends. In other words a force of 1 at a distance of 24 inches (2 feet) is equivalent to a force of 4 at a distance of 6 inches.
One of the most useful levers of this type is the wheelbarrow. The fulcrum is at the wheel, the force is at the handles, the weight is on the wheelbarrow. If the load is halfway from the fulcrum to the man's hands, the man will have to lift with a force equal to one half the load. If the load is one fourth as far from the fulcrum as the man's hands, he will need to lift with a force only one fourth as great as that of the load.
This shows that in loading a wheelbarrow, it is important to arrange the load as near to the wheel as possible.
The nutcracker is an illustration of a double lever of the wheelbarrow kind; the nearer the nut is to the fulcrum, the easier the cracking.
Hammers, tack-lifters, scissors, forceps, are important levers, and if you will notice how many different levers are used by all classes of men, you will understand how valuable a machine this simple device is.
FIG. - A slightly different form of lever.
FIG. - The wheelbarrow lightend labor.
FIG. - A modified wheelbarrow.
FIG. - The nutcracker is a lever.
FIG. - The hand exerts a small force over a long distance and draws out a nail.
FIG. - Primitive man tried to lighten his task by balancing his burden.