Understanding the Concepts of Work, Energy and Power

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The concepts of work, energy and power are very important in physics. As a physics student, you must have a very clear understanding of these three concepts. If you find yourself struggling with this concept, you should seek help from your school teacher or attend a physics tuition to anchor your understanding of this concept. In this article, we will explain the fundamentals of work, energy and power which will be applicable in your physics practices.


Work is an activity that involves displacing (moving) an object by applying force on it. When a force is applied on an object to displace (move) it over a certain distance in the direction of the force, then it is said that work is done.

Work can also be defined as the transfer of energy. When you push or lift an object, you are transferring your energy to that object so that it moves over a certain distance.

This is expressed by the following mathematical equations:

  • For a constant force in the direction of motion, the equation is W = F * d.

W is work, F is the force applied and d is the distance moved

  • For a constant force with a component in the direction of motion, the equation is W = F * d * cosq.

Theta (q) is the angle made by the force with the direction of motion.

  • For a variable force in the direction of motion, the equation is W = ò F * dx.
  • For a variable force in a variable direction, the equation is W = ò F * cosq * dx


Energy is the capacity to do work. You can think of it like money – if you have money you can buy things; if you do not have it, you cannot buy anything. No work can be done without energy. To do a certain amount of work, you need a certain amount of energy. For example, to do 100 joules of work, you have to expend 100 joules of energy.

According to the second law of thermodynamics, energy can neither be created nor destroyed. It can only be changed from one form to another, such as a car engine converts chemical energy into mechanical energy.

Energy exists in many different forms, such as thermal energy (heat), light energy (radiance), chemical energy, mechanical energy, magnetic energy, potential energy, kinetic energy and nuclear energy. They are expressed in different units, such as Joule, calorie and kWh.

The two types of energy that are of special importance to physics students are potential energy and kinetic energy.

  • Potential energy – The energy stored in an object due to its position. There are two forms of potential energy; gravitational potential energy and elastic potential energy.
  • Kinetic energy – The energy possessed by a body in motion. It is represented by the following mathematical formula: KE = 0.5 x m x v2, where m = mass of the object and v = speed of the object.


Power is the rate of doing work. It can also be defined as the rate of using energy. You can think of it as the number of times you can turn a bicycle’s wheel in a minute. The stronger you are, the more times you can turn the wheel. In the same way, the more powerful a machine is, the faster it can work.

Power is usually expressed in units of Watt. 1 Watt = 1 Joule / 1 second. If a machine does 1,000 joules of work in 1 second, then its power is 1,000 watts or 1 kilowatt. Power is also expressed in units of horsepower (hp). 1 hp = 735.7 watts.

Work, energy and power is a vast topic that requires a lot of hard work and the application questions of this concept can be very challenging. Many students take up Physics tuition in order to gain more practice so as to have a strong fundamental of this subject. Once you are well versed in the concepts, you will be able to tackle more challenging questions and work under pressure as well. If you think you are weak on this subject, do consider getting more practice on your own.