Work and energy

Work and energy

Work

Work is applied to any form of labor, pysical or mental, for producing any kind of result. In science and engineering, on the other hand, "work" has a definite technical meaning, which the following illustration will make clear.

When a man moves a box along the floor by a steady push, or raises it from the floor to the top of a table, two things should be noted: first, that the men exerts a force on the box, and second, that the box undergoes a displacement in the direction of the force. Under these contiditions the man or the force that the exerts is said to do work on the box.

The amount of work done is the product of the force and the displacement of the object while the force is being applied. In symbols, when a constant force F is exerted on an object while the object undergoes a displacement D in the direction of the the forcem the amount of work done on the object is W=FD .

Energy

A body is said to possess energy if it is able to do work. For example, a man or horse can do work and so possess energy; the steam within the cylinder of a steam engine possesses energy since it is able to move the piston; the mainspring of a watch possesses energy when woundn since it is able to drive the hands of the timepiece. Moreover, when a body does work, its energy is reduced by an amount exactly equal to the work done, Work and energy are expressed in the same units.

There are many different forms of energy; thus, the spring just mentioned has mechanical energy, a hot substance has internal energy, coal has chemical energy, a charged capacitor has electrical energy, and so on. A body or a system of bodies may posses mechanical energy from either or both of two causes. First, whenever a body is in motion it is able to exert a force and do work in coming to rest; a moving body always posses energy by virtue of its motion; this is called kinetic energy. A moving hammer has kinetic energy, and this enables it to do work in driving a nail. Second, a body that has been moved to a new position is sometimes able to do work because of this fact; for example, a raised weight can do work in falling and is commonly said to posses energy by virtue of its position; this is called potential energy.

Conservation and transformation of energy

Whenever a body does work, its capability of doing further work is lessened, and this means that it possesses less energy than before. This reduction must not be regarded as a loss of energy, for in doing work the body has imparted an equal amount of energy to some other body, which, together with the first, constitutes a system. The energy given up by a body is imparted to others without loss, and thus within the system the total amount of energy remains unchanged. This illustrates a basic principle know as the conservation of energy, which states that energy can neither be created nor destroyed. Expressed differently, the total amount of energy in the universe remains constant.

Although energy can be transformed from one kind to another, it is not destroyed in the process. When energy is expended in work against friction, it is said to be wasted, thats is, rendered unavailable for useful purposes; but it is not destroyed, for it is converted into heat, which is  recognized as form of energy.

Energy sources

This is the term aplied to the sources from which energy can be obtained to provide heat, light, and power.

Industrial society has based largely on the substitution for animal energy of power from heat of combustion of carboniferous fuels. It seems likely that it will be based in the future largely on heat from the sun and heat which is generated by nuclear reactions.

Major carboniferous fuels are coal, petroleum, and natural gas - all fossil materials formed in finite amounts many millions of years ago. Other important fossil fuels are oil shales and tar sands. Minor fuels are forms of current production of vegetation,

Nonfuel sources of energy are water, wind, terrestial heat, atmospheric electricity, and sunlught. These last supply relatively unimportant parts of the world's total used energy, but all are renewable sources of energy. The supplies of elements suitable for nuclear reactions are finite but abundant.