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By the end of the lesson, students should be able to:
  • Define Energy.
  • State and explain the different forms of energy.
  • State the Law of conservation of Energy.
  • Give the applications of the Law of conservation of Energy.


All matter possesses energy by virtue of its motion or position with respect to the forces acting on it. There are different forms of energy,which forms are convertable from one to another.

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Energy is the ability or capacity of a system to do work.

All activities in our daily life are feasible only because energy exists. We would therefore be right to say no energy, no life

Energy Forms

Kinetic and Potential Energy

Kinetic Energy
This is the type of energy associated with the motion of a body or any moving object.All bodies in motion poss kinetic energy.
Mathematically, the kinectic energy of a body is given by 1/2mv2 , where m is the mass of the body and v the velocity at which the body is moving.

Potential Energy
The word potential means hidden. A body has hidden energy depending on its position or state. This is the type of energy that is possesed by a body at rest.

Potential energy can be divided into two different forms.

  • Elastic potential energy and
  • Gravitational potential energy.

Mathematically the potential energy of a body is given by:



m is the mass of the body,
g, the acceleration due to gravity, and
h the height at which the body is from the ground.

Electrical and Magnetic Energy

  • Electrical energy: This is obtainable when other forms of energy are converted using suitable devices.For example a dynamo is able to convert kinetic energy into electrical,likewise adry cell is able to convert chemical energy to electrical.
  • Magnetic energy: some ores like iron have a tendancy to attract some materials . These ores are said to be magnetic and so posses magnetic energy .

Solar Energy and Nuclear Energy

  • Solar Energy

This is the energy that we get from the sun. The sun is actually the major source of energy from which other forms of energy are derived. For example, the solar energy from the sun is converted to chemical energy in plants.

  • Nuclear Energy
This is the energy obtained from the nucleus of the atom of elements.
Normally this energy is obtained during Nuclear fussion and Nuclear fission.
Nuclear fussion is where two lighter nuclei are combined to produce one heavy nucleus.Energy is then released.
Nuclear fission is where one heavy nucleus is split to produce two light nuclei. As a result energy is released.
The energy released appears in the form of light, sound and heat.

One important application of the nuclear energy is the formation of nuclear bombs.

Light and Sound

  • LightThis is the type of energy possesed by luminous objects,e.g the sun, moon, candles, the list is endless.Light enables us to see.Light is used in processes like;thermoic emission which is very vital in the modern physics.
  • sound This is the type of energy possesed by vibrating objects, for instance; the electric bell,tuning fork,the guitar and so on.

Heat and Geothermal

Energy Changes and Law of Consevation of Energy

The law of conservation states that energy can neither be created nor destroyed, but it can change from one form to another. This is applied whenever one wants to use one form of enegy instead of the other. For example, suppose I have solar energy, solar energy is heat and light generated by the sun. This is not the form of energy I am in need of. I am in need of the form of energy that I will use to listen to my radio. I must have a tool that can convert solar energy into electrical.

There are many other applications of energy from changes which iclude:

  • Hydro Power is obtained from running water from the top of the hill. Here kinetic enegy of water running down the hill is changed to electric energy.
  • Running air(wind) can also generate electricity from wind turbine. This is a change from kinetic energy to electrical.
  • Electrical energy form, can easily be converted to any other forms.That is why people are seriousily researching in the conversion of any other form of energy to electrical.

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The importance of energy in general has been made clear. We cannot do anything without it. Its ability to transform from one kind into another, as by law, makes it possible for us to utilise the many different forms to our convinience. The example of a dynamo converting kinetic energy into electrical energy has been mentioned. Under hydropotential energy, as energy in water in a dam higher up some lower point is usually the most commonly form used to produce hydroelectricity. Use of electricity in our daily lives no longer needs emphasis in this age.

However, not many countries or places are endowed with mountains and rivers along which points of relative height difference can be located. In countries like South Africa, much of their electricity is produced by transforming [nuclear]energy into electrical energy. The rest of their electricity is produced by burning coal.

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Self Assessment

  • Define energy?
  • Explain the different forms of energy and their sources.
  • State the principle of conservation of energy.
  • How is solar energy converted into a more useful form to provide electricity?