Power is applied to mechanical purposes—
| 1. By the lever; | 4. By the inclined plane; |
| 2. By the wheel, and axle; | 5. By the wedge; |
| 3. By the pulley; | 6. By the screw; |
which are the simple elements of all machines.
The whole theory of these elements consists simply in causing the weight, which is to be raised, to pass through a greater or a less space than the power which raises it; for, as power is compounded of the weight, or mass of a moving body, multiplied into its velocity, a weight passing through a certain space may be made to raise, through a less space, a weight heavier than itself.
THE LEVER.
The lever is the most simple of all machines, being only a straight bar of iron, wood, &c., supported on, and moveable round a prop, called the fulcrum.
Case 1.—When the fulcrum of the lever is between the power, and the weight.
Rule.—Divide the weight to be raised by the power to be applied; the quotient will give the difference of leverage necessary to support the weight in equilibrio. Hence, a small addition either of leverage, or weight, will cause the power to preponderate.
Example 1.—A ball weighing 3 tons is to be raised by 4 men, who can exert a force of 12 cwt.; required the proportionate length of lever?