Work (redirected from works up)

work, in physics and mechanics, transfer of energy by a force acting to displace a body. Work is equal to the product of the force and the distance through which it produces movement. Although both force and displacement are vector quantities, having both magnitude and direction, work is a scalar quantity, having only magnitude. If the force acts in a direction other than that of the motion of the body, then only that component of the force in the direction of the motion produces work. Thus when a 5-lb (22.4-newton) force pulls a body 10 ft (3 m), it does 50 foot-pounds (67.2 meter-newtons) of work. If a force acts on a body constrained to remain stationary, no work is done by the force. Even if the body is in motion, the force must have a component in the direction of motion. Thus, any centripetal force, such as the sun's gravitational pull on the earth, does no work because it acts at right angles to the motion and has no component in that direction (see centripetal force and centrifugal force). When there is no friction and a force acts on a body, the work done by the force is equal to the increase of the kinetic and potential energy of the body, since all the energy expended by the agency exerting the force must be gained by the body. If frictional forces are present, then some of the work must go to overcome friction and appears finally in the form of heat energy. A simple machine is a device for converting work into another form of energy. For example the jackscrew converts an input of work done on the machine to raise the load. The efficiency of a machine, which is defined as the ratio of the work output to the work input, is always less than one, since some of the input is invariably wasted in overcoming friction. The element of time does not enter into the computation of work; the time rate of doing work is called power. One horsepower is an expenditure of 33,000 foot-pounds per minute. Some of the units used to measure work are the foot-pound, the erg, and the joule.

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work

In economics and sociology, the activities and labour necessary for the survival of society. As early as 40,000 BC, hunters worked in groups to track and kill animals, while younger or weaker members of the tribe gathered food. When agriculture replaced hunting and gathering, the resulting surplus of food allowed early societies to develop and some of its members to pursue crafts such as pottery, weaving, and metallurgy. Historically, rigid social hierarchies caused nobles, clergy, merchants, artisans, and peasants to pursue occupations defined largely by hereditary social class. Craft guilds, influential in the economic development of medieval Europe, limited the supply of labour in each profession and controlled production. The establishment of towns led to the creation of new occupations in commerce, law, medicine, and defense. The coming of the Industrial Revolution, spurred by technological advances such as steam power, changed working life profoundly. Factories divided the work once done by a single craftsman into a number of distinct tasks performed by unskilled or semiskilled workers (see division of labour). Manufacturing firms grew larger in the 19th century as standardized parts and machine tools came into use, and ever-more-specialized positions for managers, supervisors, accountants, engineers, technicians, and salesmen became necessary. The trend toward specialization continued into the 21st century, giving rise to a number of disciplines concerned with the management and design of work, including production management, industrial relations, personnel administration, and systems engineering. By the turn of the 21st century, automation and technology had spurred tremendous growth in service industries.

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work

In physics, the measure of energy transfer that occurs when an object is moved over a distance by an external force, some component of which is applied in the direction of displacement. For a constant force, work W is equal to the magnitude of the force F times the displacement d of the object, or W = Fd. Work is also done by compressing a gas, by rotating a shaft, and by causing invisible motions of particles within a body by an external magnetic force. No work is accomplished by simply holding a heavy stationary object, because there is no transfer of energy and no displacement. Work done on a body is equal to the increase in energy of the body. Work is expressed in units called joules (J). One joule is equivalent to the energy transferred when a force of one newton is applied over a distance of one metre.

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Work

In physics, the term work refers to the transference of energy that occurs when a force is applied to a body that is moving in such a way that the force has a component in the direction of the body's motion. Thus work is done on a weight that is being lifted, or on a spring that is being stretched or compressed, or on a gas that is undergoing compression in a cylinder.

When the force acting on a moving body is constant in magnitude and direction, the amount of work done is defined as the product of just two factors: the component of the force in the direction of motion, and the distance moved by the point of application of the force. Thus the defining equation

for work W is given below, where f and s are the magnitudes of the force and displacement, respectively, and &phgr; is the angle between these two vector quantities (see illustration). Because f cos &phgr; · s = f · s cos &phgr; work may be defined alternatively as the product of the force and the component of the displacement in the direction of the force.

Work of constant force f is fs cos &phgr;

The work done is positive in sign whenever the force or any component of it is in the same direction as the displacement; one then says that work is being done by the agent exerting the force and on the moving body. The work is said to be negative whenever the direction of the force or force component is opposite to that of the displacement; then work is said to be done on the agent and by the moving body. From the point of view of energy, an agent doing positive work is losing energy to the body on which the work is done, and one doing negative work is gaining energy from that body.

The work principle, which is a generalization from experiments on many types of machines, asserts that, during any given time, the work of the forces applied to the machine is equal to the work of the forces resisting the motion of the machine, whether these resisting forces arise from gravity, friction, molecular interactions, or inertia.

The work done by any conservative force, such as a gravitational, elastic, or electrostatic force, during a displacement of a body from one point to another has the important property of being path-independent: Its value depends only on the initial and final positions of the body, not upon the path traversed between these two positions. On the other hand, the work done by any nonconservative force, such as friction due to air, depends on the path followed and not alone on the initial and final positions, for the direction of such a force varies with the path, being at every point of the path tangential to it. See Energy, Force