Machines
The beginning time machines how it works: some old age machines and their uses.
A machine may be defined as any device that takes advantage
of one or more fundamental mechanical principles to reduce human
effort. When we think of machinery we naturally think of something very
complicated, such as a printing press, an automobile, or a Linotype machine. We
just see the fundamental mechanical principles such as the wheel axle and
pulleys.
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The wheel and axis
The wheel and axle consist of a crank or a wheel fastened to a
drum or axle, and the law of the lever applies to it and to levers. The length
of the crank, or the radius of the wheel, is equivalent to the effort arm of
the lever, and the radius of the drum or axle is equivalent to the resistance
arm of the lever. The effort times the wheel radius always equals the resistance
times the axle radius.
If the radius of the wheel or the length of the crank is very
large and the radius of the axle is tiny, the mechanical advantage of
this machine is great, and a small turning force on the crank will produce a
great turning force on the axle. Here again, the principle of work applies, for
the work done by the effort or crank equals the work done upon the resistance
of the axle.
To take a simple example, consider the crank attached to an axle. Suppose
the length of the crank is two feet and the radius of the axle is 2 inches. The
distance travelled by the crank in one revolution will be twelve times the
distance travelled by the axle in one revolution, and every pound of force
exerted on the crank will produce twelve pounds of force in the axle.
If a rope
is attached to the axle and this rope winds as we turn the crank, we, by
exerting a force of 10 pounds on the crank, pull or lift 120 pounds, and the
mechanical advantage is 12. Of course, the through which we pull or lift this
weight will be only one-twelfth of the distance through which we move the
crank.
The ice cream freezer, the clothes wringer, the
meat grinder, the winch, and the capstan are all examples of the wheel and axle.
Pulleys
The pulley is a wheel and axle in which no force is applied
to the axle. Both the effort and the resistance are applied to the rim of the
wheel, and if the pulley is single and fixed, there is no mechanical advantage.
The only advantage that a single fixed pulley has is that it causes a change in direction. A flag is hoisted to the top of the pole utilizing a
pulley; a given weight may be sent up and down or in and out with constant change
of direction using several single pulleys.
If two pulleys are rigged up, the upper one becomes a single
fixed pulley and the lower one becomes a movable pulley. By pulling on the rope
at E you can readily see that the lower pulley will move up toward the upper pulley-but
it will move just half as fast and it will take just twice as long to lift a
weight with this system as it did with a single fixed pulley. By the principle
of work, we know what we lose in distance we gain in force and vice versa.
The wedge
The wedge is nothing more than a thin piece of wood or metal
with sloping sides that come to a knife edge. It is used in all cutlery and
cutting tools such as the knife, the axes, the chisel, and others. The wedge is
also used to tighten loose objects as when a window rattles or when a door won’t
stay open; its principal use is in cutting tools.
Now it is invaluable. In modern
machine shop work the use of tools with cutting edges, both for woodworking as
well as for cutting, drilling, boring, and milling metals, the principle of the
wedge is indispensable. The ordinary needle is a simple wedge. So you can see
how important the wedge is to the clothing industry.
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technology