The concepts of work, energy, and power are fundamental in physics and are closely related to each other. Let’s explore each concept individually:

1. Work

In physics, work is defined as the transfer of energy that occurs when a force is applied to an object, and the object is displaced in the direction of the force. Mathematically, work (W) is calculated as the product of the force (F) applied on an object and the displacement (d) of the object in the direction of the force: W = F × d × cosθ, where θ is the angle between the force and the displacement vectors. The SI unit of work is the joule (J).

2. Energy

Energy is a scalar quantity that represents the ability of a system to do work or to cause changes. It exists in various forms, such as kinetic energy, potential energy, thermal energy, chemical energy, etc. The total energy of a closed system remains constant, according to the law of conservation of energy. The SI unit of energy is also the joule (J).

Kinetic Energy: Kinetic energy is the energy possessed by an object due to its motion. It depends on the mass (m) of the object and its velocity (v). Mathematically, kinetic energy (KE) is given by the equation KE = (1/2)mv^2.

– Potential Energy: Potential energy is the energy possessed by an object due to its position or condition. There are various types of potential energy, such as gravitational potential energy, elastic potential energy, and chemical potential energy. Gravitational potential energy (PE) depends on the height (h) of an object and its mass (m) in a gravitational field. The equation for gravitational potential energy is PE = mgh, where g is the acceleration due to gravity.

3. Power

Power is the rate at which work is done or energy is transferred or transformed. It measures how quickly work is done. Mathematically, power (P) is defined as the work done (W) per unit of time (t): P = W/t. The SI unit of power is the watt (W), which is equal to one joule per second.

– Average Power: Average power is calculated by dividing the total work done by the total time taken: P_avg = W_total / t_total.

Instantaneous Power: Instantaneous power refers to the power at a specific moment in time. It can be calculated as the derivative of work with respect to time: P_inst = dW/dt.

These concepts of work, energy, and power are interconnected and play a crucial role in understanding and analyzing various physical phenomena and systems.

Work is the product of force and distance moved in a given direction and the quantity of work done 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(f x d). Work can simply be defined as the product of distance moved and the force applied in the direction of movement.

Generally, for any work done, there must be energy input since energy is the capacity of any system or 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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