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The Law of Conservation of Energy and Energy Transfer

Grade 4
Aug 3, 2023


The law of conservation of energy states that energy is neither created nor destroyed but changed from one form to another. 

Example: The objects in the images possess potential energy because of their special shape and position.

Fig-1: Potential energy is possessed by the objects in the image

When the shape or position of objects is disturbed, they are said to be in motion.

Fig-2: Kinetic energy is possessed by the objects in motion


The energy possessed by the objects in motion is kinetic energy. In all these examples, the transfer of energy is taking place. The potential energy of the objects is converted into kinetic energy.

Mechanical energy is the sum of the kinetic energy and the potential energy of the body. 

M.E = K.E + P. E, i.e.,

Mechanical energy = potential energy + kinetic energy = constant

Energy transformation takes place, but the total energy always remains conserved.



Different Types of Energy Transfer and Conversions:

  1. A flashlight converts chemical energy stored in a battery into light energy.
  2. An engine of a vehicle converts chemical energy (petrol or diesel) into kinetic energy.
  3. Mechanical energy can be converted to electrical energy by generators, and the reverse, the conversion of electrical energy to mechanical energy, can be accomplished by motors.
  4. A battery is a device that converts chemical energy to electrical energy. For some batteries, this is a process that cannot be reversed, but for others, it can. Batteries for which the process can be reversed are called rechargeable batteries.
  5. Every living plant converts light energy, which they get from the sunlight, into chemical energy through photosynthesis.
  6. In an electric bulb, the electricity heats the filament of the bulb; when it becomes very hot, it starts producing light. Similarly, in toasters, room heaters, and geysers, the conversion of electrical energy into heat energy takes place.
  7. A speaker and an alarm clock convert electrical energy into sound energy.
  8. In a grinder, washing machine, and fan, the conversion of electrical energy into mechanical energy takes place; as in all these devices, some parts rotate when electricity is supplied to them. They all contain a motor that converts electrical energy into mechanical energy.
  9. We human beings get energy from food and do mechanical work. So, the stored chemical energy in the food gets converted into mechanical energy when we do work. We get energy from food after digestion.
  10. Energy generated from the Sun is due to a nuclear reaction taking place in the Sun. The energy of the Sun is nuclear energy that changes into heat or thermal energy because of a nuclear reaction.
  11. A solar cell and solar panel convert solar energy into electrical energy in the presence of sunlight.


  • Energy is defined as the ability of a body to do work.
  • Energy exists in different forms. Something constructive happens only when energy is transferred from one form to another.
  • The work done is the measure of the amount of energy transferred.  All forms of energy as well as work, are measured in Joules.
  • The law of conservation of energy states that energy is neither created nor destroyed, but changes from one form to another. 
Law of Conservation of Energy


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