A simple machine is a mechanical device that changes the direction or magnitude of a force.[1] In general, they can be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force.[2] Usually the term refers to the six classical simple machines that were defined by Renaissance scientists:[3][4][5]
Basic Machines And How They Work
Although they continue to be of great importance in mechanics and applied science, modern mechanics has moved beyond the view of the simple machines as the ultimate building blocks of which all machines are composed, which arose in the Renaissance as a neoclassical amplification of ancient Greek texts. The great variety and sophistication of modern machine linkages, which arose during the Industrial Revolution, is inadequately described by these six simple categories. Various post-Renaissance authors have compiled expanded lists of "simple machines", often using terms like basic machines,[9] compound machines,[6] or machine elements to distinguish them from the classical simple machines above. By the late 1800s, Franz Reuleaux[11] had identified hundreds of machine elements, calling them simple machines.[12] Modern machine theory analyzes machines as kinematic chains composed of elementary linkages called kinematic pairs.
During the Renaissance the dynamics of the mechanical powers, as the simple machines were called, began to be studied from the standpoint of how far they could lift a load, in addition to the force they could apply, leading eventually to the new concept of mechanical work. In 1586 Flemish engineer Simon Stevin derived the mechanical advantage of the inclined plane, and it was included with the other simple machines. The complete dynamic theory of simple machines was worked out by Italian scientist Galileo Galilei in 1600 in Le Meccaniche (On Mechanics), in which he showed the underlying mathematical similarity of the machines as force amplifiers.[17][18] He was the first to explain that simple machines do not create energy, only transform it.[17]
Although each machine works differently mechanically, the way they function is similar mathematically.[20] In each machine, a force F in \displaystyle F_\textin is applied to the device at one point, and it does work moving a load F out \displaystyle F_\textout at another point.[21] Although some machines only change the direction of the force, such as a stationary pulley, most machines multiply the magnitude of the force by a factor, the mechanical advantage
Simple machines do not contain a source of energy,[22] so they cannot do more work than they receive from the input force.[21] A simple machine with no friction or elasticity is called an ideal machine.[23][24][25] Due to conservation of energy, in an ideal simple machine, the power output (rate of energy output) at any time P out \displaystyle P_\textout is equal to the power input P in \displaystyle P_\textin
In many simple machines, if the load force F out \displaystyle F_\textrm out on the machine is high enough in relation to the input force F in \displaystyle F_\textrm in , the machine will move backwards, with the load force doing work on the input force.[29] So these machines can be used in either direction, with the driving force applied to either input point. For example, if the load force on a lever is high enough, the lever will move backwards, moving the input arm backwards against the input force. These are called reversible, non-locking or overhauling machines, and the backward motion is called overhauling.
However, in some machines, if the frictional forces are high enough, no amount of load force can move it backwards, even if the input force is zero. This is called a self-locking, nonreversible, or non-overhauling machine.[29] These machines can only be set in motion by a force at the input, and when the input force is removed will remain motionless, "locked" by friction at whatever position they were left.
There are only six simple machines: the lever, the block, the wheel and axle, the inclined plane, the screw, and the gear. Physicists, however, recognize only two basic principles in machines: those of the lever and the inclined plane. The wheel and axle, block and tackle, and gears may be considered levers. The wedge and the screw use the principle of the inclined plane.
Mechanical engineering includes all aspects of design, development,control, and manufacture of mechanical systems and energy conversionsystems. Mechanical engineering is essential to the proper design andmanufacture of nearly every physical product in our modern world. Assuch, mechanical engineers are a fundamental resource for mostindustries, and they work in interdisciplinary environments. Mechanicalengineers must have the ability to see both broad perspectives acrossdisciplines and industries, and solve very local and specializedproblems. The undergraduate curriculum addresses the education andtraining of mechanical engineering students and concentrates on twotechnical areas: (1) design and analysis of thermofluid systems foreffective use of energy; and (2) design, analysis, and control ofmechanical systems including the use of materials. The MechanicalEngineering educational program develops future engineers with a solidunderstanding of fundamentals and competence in analyzing engineeringsystems.
Laboratory course that provides supervised evening access to the machineshop and/or light fabrication area for qualified mechanical engineeringstudents to work on their University-directed projects. Students wishingto utilize the machine shop or light fabrication during the eveninglab/shop hours are required to enroll. Enrollment in any section allowsstudents to attend any/all evening shop hours on a drop-in basis. Staffor faculty will be present during each scheduled meeting to supervise aswell as be available for consultation and manufacturing advising.Prerequisites: Students must be qualified for machine shop use throughsuccessful completion of MECH 101L and passing grade on the MechanicalEngineering Lab Safety Test. Qualifications for light fabrication areause: successful completion of the Light Fabrication Training Seminar anda passing grade on the Mechanical Engineering Lab Safety Test. P/NP. (1unit)
When a group of people abandons a place where they once lived and worked, they may leave behind many things. "Material culture" or "artifacts" like parts of the buildings they lived in, the objects and machines they once used, or a garbage dump may remain today from peoples of the past. Photographs, diaries, or ledgers may also be recovered through painstaking work. Historical archeologists study all these items (both written records and non-written artifacts) to learn about the people that left these things behind.
Without archeology we might not know much about how the miners at Johnson Lake Mine operated the mine and what their daily lives were like. Using archeological skills to examine the evidence, we can study what they ate, where they slept, what tools they used, how they worked, and what "treasures" they may have left behind.
At the trial of an action by one employed in a cotton mill to recover for personal injuries alleged to have been received by the plaintiff by reason of a failure of the defendant to warn him of the dangerous character of a machine upon which he was working, there was evidence tending to show that the plaintiff had been set to work before the accident by a superintendent of the defendant at cleaning rapidly revolving cylinders of carding machines, no one of which had attached to it an appliance called a licker-in, that a licker-in was another smaller cylinder with teeth upon it, which revolved on a separate axis outside of and in the opposite direction from, but close to, the main cylinder which the plaintiff was cleaning; that just before the accident the plaintiff was set to work cleaning the cylinder of a machine which had a licker-in that was wrapped up so that he could see only, the wrappings, that he never had seen a licker-in and did not know of its character; that the superintendent who set him to work upon the machine with the licker-in had not warned him of its character, but had delegated the duty of instructing him to one who was not in the employ of the defendant, and that such person had not warned him of the character of the licker-in; that, while he was cleaning the main cylinder as he had been told to do, a stick that he was using slipped and his hand was drawn between the cylinders and was injured on the teeth of the licker-in. Held, that the questions, whether the plaintiff was in the exercise of due care, whether there was an obvious risk of injury or one which he assumed, and whether the defendant was negligent as alleged, were for the jury.
At the trial, which was before Dana, J., the plaintiff testified that at the time of his injury he was nineteen years of age and had been working for the defendant less than a month; that he never had worked as an operative in a mill nor had he ever operated any machinery; that, when he went to work for the defendant, he was hired by one Allen, who was his boss and told him what to do; that, about a week before the accident, Allen set him to work cleaning carding machines and had just started to show him how when a man named Schoules came along and Allen said "This gentleman will show you how to do it," and walked away. Schoules then showed him. After he had been at work as directed for a week, he was put to work at cleaning a carding machine which had a different appliance upon it, which, after the accident, he learned was a licker-in. This appliance is described in the opinion. He discovered that he could not work as he had been directed to with the other machines, and returned to bench work, when Allen came to him and told him to go back to work on the machine. Schoules, who was passing by, thereupon instructed him in a new way to work, adapted to the machine with the new appliance, but did not warn him in any way of the dangers attending cleaning the machine with the licker-in on it. The licker-in was wrapped in paper and the plaintiff could not see that it had teeth. He had seen no such appliances around the mill.
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