Climate Change. Climate Feedback. Ocean Acidification. Rising Sea Level. Mechanical advantage. The inclined plane is a simple device that hardly looks like a machine at all.
The mechanical advantage increases as the slope of the incline decreases. But the load will then have to be moved a greater distance. The ideal mechanical advantage IMA of an inclined plane is the length of the incline divided by the vertical rise, the so-called run-to-rise ratio. The mechanical advantage increases as the slope of the incline decreases, but then the load will have to be moved a greater distance.
Again, work in equals work out in an entirely efficient system. Friction will be large if objects are slide along the surface of the inclined plane. Efficiency can be increase by using rollers in conjunction with the inclined plane.
The wedge is an adaptation of the inclined plane. It can be used to raise a heavy load over a short distance or to split a log. The ideal mechanical advantage IMA of a wedge depends on the angle of the thin end.
The smaller the angle, the less the force required to move the wedge a given distance through, say, a log. At the same time, the amount of splitting is decreased with smaller angles.
The screw is actually an inclined plane wrapped in a spiral around a shaft. A jackscrew combines the usefulness of the screw and the lever.
The lever is used to turn the screw. The ideal mechanical advantage IMA of a screw is ideally the ratio of the circumference of the screw to the distance it advances during each revolution. Machine screws, working their way through a nut, can be relatively efficient.
This was even true to some extent with the steam engine, first developed late in the seventeenth century and brought to fruition by Scotland's James Watt Yet the steam engine, though it involved ordinary mechanical processes in part, represented a new type of machine, which used thermal energy. This is also true of the internal-combustion engine; yet both steam-and gas-powered engines to some extent borrowed the structure of the hydraulic press, one of the three basic types of machine.
Then came the development of electronic power, thanks to Thomas Edison and others, and machines became increasingly divorced from basic mechanical laws. Photograph by E. Reproduced by permission. The heyday of classical mechanics—when classical studies in mechanics represented the absolute cutting edge of experimentation—was in the period from the beginning of the seventeenth century to the beginning of the nineteenth.
One figure held a dominant position in the world of physics during those two centuries, and indeed was the central figure in the history of physics between Galileo and Albert Einstein This was Sir Isaac Newton , who discerned the most basic laws of physical reality—laws that govern everyday life, including the operation of simple machines.
Newton and his principles are essential to the study that follows, but one other figure deserves "equal billing": the Greek mathematician, physicist, and inventor Archimedes c. Nearly 2, years before Newton, Archimedes explained and improved a number of basic machines, most notably the lever. Describing the powers of the lever, he is said to have promised, "Give me a lever long enough and a place to stand, and I will move the world. A common trait runs through all forms of machinery: mechanical advantage, or the ratio of force output to force input.
In the case of the lever, a simple machine that will be discussed in detail below, mechanical advantage is high. In some machines, however, mechanical advantage is actually less than 1, meaning that the resulting force is less than the applied force. This does not necessarily mean that the machine itself has a flaw; on the contrary, it can mean that the machine has a different purpose than that of a lever. One example of this is the screw: a screw with a high mechanical advantage—that is, one that rewarded the user's input of effort by yielding an equal or greater output—would be useless.
In this case, mechanical advantage could only be achieved if the screw backed out from the hole in which it had been placed, and that is clearly not the purpose of a screw. Here a machine offers an improvement in terms of direction rather than force; likewise with scissors or a fishing rod, both of which will be discussed below, an improvement with regard to distance or range of motion is bought at the expense of force.
In these and many more cases, mechanical advantage alone does not measure the benefit. Thus, it is important to keep in mind what was previously stated: a machine either increases force output, or changes the force's distance or direction of operation. Most machines, however, work best when mechanical advantage is maximized. Yet mechanical advantage—whether in theoretical terms or real-life instances—can only go so high, because there are factors that limit it.
For one thing, the operator must give some kind of input to yield an output; furthermore, in most situations friction greatly diminishes output. Hence, in the operation of a car, for instance, one-quarter of the vehicle's energy is expended simply on overcoming the resistance of frictional forces. For centuries, inventors have dreamed of creating a mechanism with an almost infinite mechanical advantage. This is the much-sought-after "perpetual motion machine," that would only require a certain amount of initial input; after that, the machine would simply run on its own forever.
As output compounded over the years, its ratio to input would become so high that the figure for mechanical advantage would approach infinity. A number of factors, most notably the existence of friction, prevent the perpetual motion machine from becoming anything other than a pipe dream.
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