work_ energy and power by AbdoAbdullahAbdo


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Huge source of energy
 The Sun, is a huge nuclear reactor - NATURAL NUCLEAR REACTOR - where each second more than 4000 kg
of matter are transformed into energy equivalent to almost 92 billion megatons of TNT!.
                                                    In ordinary conversation the word " work" refers to almost any kind
                                                  of physical or mental activity, but in science and mathematics it has
                                                  one meaning only. Work is done when a force produces motion. An
                                                  engine pulling a train does work; so does a crane when it raises a
                                                  load against the pull of the earth. Similarly, a workman who is
                                                  employed to carry bricks up a ladder and on to a scaffold platform
                                                  also performs work. On the other hand, a man carries a heavy weight
                                                  on his shoulders and does not move for a long time, must have
                                                  become tired, but, technically speaking, he did no work on that heavy
                                                    Nevertheless, when a person holds a heavy load some internal work
                                                  is done by continuous expansion and contraction of his muscular
                                                    Work is said to be done when the point of application of a force
                                                  moves and is measured by the product of the force and the distance
                                                  moved in the direction of the force.
 Work = force × distance moved in the direction of the force.
  W =F×d
   Work is energy transferred to or from an object by means of a force acting on the object. Energy transferred to
the object is positive work, and energy transferred from
the object is negative work. ( I'll come to that part later )
    The SI unit of work ( and energy ) is called the joule ( J ) and is the work done when the point of a force of 1
newton ( N ) moves through 1 metre ( m ) in the direction of the force.
  Larger units used are kilojoule ( kj ) and the megajoule ( M J ). There is a unit of heat " calorie " .
      1 jk    = 1000 j
      1 MJ     = 1000000 j
      1 calorie = 4.148 j
 It follows that an engine which exerts a force of 5000 N over a distance of 4 m will do5000 × 4 = 20000 j, or 20 kj.
 If we wish to calculae the work done by a man of mass 70 kg in climbing a ladder 5 m high, we first calculae his
weight ( force ) :
 F = mg = 70 × 9.8 = 686 N
 Thus, the work is
    W =F×d
    W = 686 × 5 = 3430 j.

Anything which is able to do work is said posses energy, and therefore
    Energy is the capacity to perform work
    Work and energy are, of course, both measured in the same units, as mentioned above.
    Forms of enegy:
        The world we live in provides energy in many different forms, of which the most important has been chemical
energy. The utilization of the latent chemical energy in coal, oil and gas, rekeased in the form of heat to drive steam
turbines and internal-combustion engines, has been a major factor in the development of modern civilization.
        Many of the material comforts which we enjoy today come from the use of electric energy. The first
electricity generating plants were powerd by steam engines,but by the middle of the twenteith century large
hydro-electric power installations has been built in countries all over the world. " Hydro-electric" means the
production of electricity by generators driven by water turbines. The rapid flow of water required for this purpose
                                                          comes from big reservoirs formed by building dams across valleys
                                                          and large rivers.
                                                                  Windmills which convert the energy of wind into mechanical
                                                          energy in machinery have long been in use for working water pumps
                                                          as well as for milling grain or sawing timber. In some parts of the
                                                          world where the sun shines uninterruptedly for long periods, large
                                                          concave mirrors have been set up to collect energy directly from the
                                                          sun by focusing its rays on to special boilers which provide power for
                                                          running small generators.
                                                                  The utilization of atomic energy, which began after the middle
                                                          the twenteith century, has made available a new source of heat as a
                                                          link in the production of electricity.

                                                Mechanical energy
                                               In machines, energy is divided into two kinds called potential and
                                              kinetic energy ( p.e and k.e. ).
                                                  kinetic energy is the energy which a body has by reason of its
   Potential energy is the energy something has by reason of its position or state.
   Obvious examlpes of kinetic energy are moving bulletts or hammer heads. These are able to do work by
overcoming forces when they strike something. A heavy flywheel stores energy in the form of rotational kinetic
energy and so keeps an engine running smoothly in between the working strokes of its pistons.

    One of the commonest forms of Potential energy is that possessed by a body when it is above the level of the
earth's surface. When something is lifted vertically, work is done against its weight and this work becomes stored up
in the body as gravitational potential energy.
    Another example is the elastic potential energy stored up in a wound clock-spring. I have no energy to complete
now , so .. to be continued :) .

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