Other Very Simple Machines

A loss in path as payment for a gain in force is a general law not only for levers but also for all other devices and mechanisms used by man.

A tackle is widely used for lifting loads. This is what we call a system consisting of several movable pulleys joined to one or several fixed pulleys. The load in Figure 1 is suspended by six strings. It is clear that the weight is distributed among the strings, and so the tension in a string will be six times less than the weight. The lifting of a one-ton load will require an application of . However, it is not difficult to see that in order to raise the load by , one must haul in of string. For raising the load by , of work are needed. We must supply this work in “some form”—a force of must act along a path, a force of along a path, and a force of along a path.

An inclined plane, which we discussed here, is also a device permitting a gain in force at the expense of a loss in path.

A blow is a distinctive means of multiplying forces. A blow with a hammer, an axe, a ram and even a blow with a - fist can create an enormous force. The secret of a strong blow isn’t complicated. Driving a nail into an unyielding wall with a hammer, one must take a good wind-up. A big swing, i.e. a long path along which the force acts, generates a significant kinetic energy in the hammer. This energy is released along a small path. If the swing covers and the nail enters into the wall, the force is intensified by a factor of 100. But if the wall is harder and the nail, after the same swing of the hand, enters into the wall, the blow will be ten times as strong as in the former case. The nail does not enter a hard wall as deeply, and the same work is expended on a shorter path. It turns out that a hammer works like an automaton: it strikes harder where the wall is harder.

If a hammer of is “speeded up”, it will strike a nail with a force of . Also, in splitting logs with a heavy wood-chopper, we break the wood with a force of several thousands ’s. Heavy forging hammers fall from small heights, of the order of a metre. Flattening a forged piece by 1 mm–2 mm, a hammer of comes down on it with an enormous force, that of .