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Work is the product of force and distance moved in a given direction and the quantity of workdone is always equal to the quantity of energy put in.

In science, work is said to be done when a force can produce movement in a measured direction i.e. work=force(f)x distance(d) moved in the direction of the force(fxd). Work can simply be defined as the product of distance moved and the force applied in the direction of movement.

Generally for any workdone, there must be energy input since energy is the capacity of any system or a body to do work. Both work and energy are measured in units called joules, named after a Scientist P. Joules who carried out early studies on energy.

Force is that which changes a body’s state of rest or uniform motion in a straight line. It can be expressed as:

Force=Mass x acceleration

i.e. F=m x a

where F =force, m =mass and a = acceleration. The unit of force is Newton (N)

If force=mass x acceleration

Work=mass x acceleration x distance



The sun is the primary source of energy available for man. It does not deplete, and cannot be used up.

The sun transmits solar energy to the earth in the form of light and heat and this solar energy can be transformed to other forms.

Solar energy is used by green plants to manufacture their food through the process of photosynthesis. The energy stored up in green plants is made available to man and animals when they eat plant products like yam, rice, cassava, beans grasses and so on.

In addition, solar energy can be converted to other energies such as to chemical and electrical energy for heating in homes, boiling water and for lighting our homes and streets.

Hence, the sun is the primary source of energy for life, all other sources are secondary as they are obtained from the sun.

Examples of secondary sources are

  1. Food
  2. Petrol
  3. Wood,
  4. Water


6.Magnet and



There are many forms of energy which can be converted from one form to the other. These are some of the forms of energy.

1.Mechanical Energy

2.Kinetic Energy

3.potential energy

4.chemical energy

5.Atomic energy

6.sound energy

7.Electrical energy

8.Light energy

9.Heat energy and

10.Magnetic energy


1.Mathematical expression of power is ——————

  1. Newton/Distance b. Force/Time c. Workdone/Time   d. Mass/Density

2.Energy obtained in food is ——————–

  1. Power b. Food c. Chemical d. Solar   e. Nuclear

3.Mathematical expression for work done by a body is represented below as ——–a. W = fxd   b. W = n xt c. S=d xt d. W=m xv e. W=f Xj

4.The S.I unit of force is ————

  1. N b. NM c. M d. G


1.Name five different sources of energy.

2.Explain why the sun is the primary source of energy?

3.Name the different forms of Energy.

See also:



Electrical Energy




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