Work, energy and power

• Energy is the ability of an object to produce movement or

  changes.

  There are many types of energy such as light energy, thermal

  energy, kinetic energy, etc.
• Kinetic energy is energy of a moving object.

  KE= ½ mv2 where m=mass(kg) and v=speed(m/s)
• Potential energy is stored energy of an object at certain height.

  PE= m.g.h where m=mass(kg), g=gravity, h=height(m)
• Mechanical energy is total of KE and PE

  ME= KE+PE
• Work is measure of energy transfer that occurs when an object

  is moved over a distance by an external force.

  Work is also change of energy.

  Work = Force x displacement
• Principle of Energy or

  conservation of energy:

  ‘Energy can not be created nor

  destroyed, it only changes its

  forms.’
• Energy transforms itself from one type to another.

  For example in collision: Some of kinetic energy from the movement of both vehicles are changed into heat, deformation of the cars and sound.
• Assumption: If the objects at frictionless surface or in vacuum (no air).

  Under this assumption we can say the mechanical energy is conserved, which means all the potential energy will be changed into kinetic energy eventually and vice versa.

  So at any point:

  Mechanical Energy is always the same

  =

  The sum of Kinetic Energy and Potential Energy
• Power is the rate at which work is done, or the rate at which

  energy is transferred.

  • power is measured in watts (W)
  • work done or energy transferred is measured in joules (J)
  • time is measured in seconds (s).

  power = work done / time taken

  P = W / t
• Efficiency is the ratio of useful work done by a device, to the total work done (or the ratio of useful output energy to the total energy input).

  Efficiency is often expressed as a percentage.

  efficiency = useful work done / total work done

  Efficiency is always less than 100%, as no device is perfect and

  some energy is always lost.
• • The sun is the source of energy of our solar system. This energy is absorbed by the earth systems and this earthly resources can be transformed into electricity.
  • The resources which are limited called non renewable resource of energy such as oil, gas and coal.
  • The resources which are long lasting is called renewable resource of energy such as solar, biogas and hyropower.