Sunday, January 8, 2012

Work, energy and power

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!.
 Work
  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 weight.
  Nevertheless, when a person holds a heavy load some internal work is done by continuous expansion and contraction of his muscular fibers.

  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 do 5000 × 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.


   Energy 
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 motion.
      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  :) .