In this blog, we are going to learn about work energy and power. One of the most important physical concepts is the concept of energy. Energy is the capacity to do work. Life is impossible without energy. When we eat, our bodies digest the food to release energy, so that we can work. When we work or walk we do some physical work, so here again we use energy. Energy lights our cities move our vehicles and runs our industries.

What is Energy?

In science, the term energy has a very precise and definite meaning. The energy of an object is defined as its capacity to do work and is measured by the total amount of work it can do, for example, a man or a horse when pulls a load is said to possess energy.

If a moving body sets the other bodies into motion after the collision, then it is said to possess energy. The mainspring of a watch when turned around, drives the hands of a watch and does work. It is also said to possess energy. So we can conclude that anything which is able to do work, is said to possess energy. So we can say that the ability to do work is called energy.

The object which does the work loses energy and the object on which the work is done gains energy.

Unit of Energy

The SI unit of energy is the same as that of work i.e. Joules, which is symbolized using the symbol J.

Types of Energy

How does an object with energy do work? When an object that possesses energy exerts a force on another object, it transfers its energy to the other object. The second object may move as it receives energy and therefore it may also do some work. This implies that any object that possesses energy can do work.

There are various forms of energy such as:

1. Solar energy
2. Heat energy
3. Wind energy
4. Chemical energy
5. Hydro energy
6. Electrical energy
7. Magnetic energy
8. Light energy
9. Nuclear energy
10. Mechanical energy
11. Kinetic energy
12. Potential energy

Rate of Doing Work

In this section of work energy and power, we will learn about the rate of doing work. Have you ever wondered do all of us work at the same rate? Do different machines consume and transfer energy at the same rate? Let us look at this activity to understand this better! Consider two children A and B of nearly the same weight. Both start running separately. Both reach a run for 50 meters. Let us say it takes 15 sec, while B takes 20 seconds, to accomplish the task.

Can you tell what is the work done by each child? The work done is the same. However, A has taken less time than B to do the work. But who has done more work in a given time, say in 1 second?

Obviously, it is A, who has done more work, since he has covered the same distance in less time. A stronger person may do certain work in relatively less time. A more powerful vehicle would complete a journey in a shorter time, than a less powerful one. We talk of the power of machines like motorbikes, and motorcars. The speed with which these vehicles change the energy or do work is a basis for their classification.

Power

Power measures the speed of work done, that is, how fast or slow work is done. Power is defined as the rate of doing work or the rate of transfer of energy. If an agent does a work W in time t, then power is given by:

Power=Work/Time

Unit of Power

The SI unit of power is watt (W) in honour of James Watt having the symbol W.

1 watt is the power of an agent, which does work at the rate of 1 joule per second. We can also say that power is 1 Watt when the rate of consumption of energy is 1 J/s.
1 watt = 1 joule/second or 1 W = 1 J/s. We express larger rates of energy transfer in kilowatts (kW).

• 1 Kilowatt = 1000 watts
• 1 kW = 1000 W
• 1 kW = 1000 Js^-1

It is very important to understand that, the power of an agent may vary with time. This means that the agent may be doing work at different rates at different intervals of time. Therefore the concept of average power is useful. We obtain average power by dividing the total energy consumed by the total time taken.

Average power = (total energy consumed)/(total time taken)

Work

Scientific Conception of Work: To understand the way we view work and define work from the point of view of science, let us consider some situations:

1. Push a box lying on a surface. The box moves through a distance. You exerted a force on the box and the box got displaced.

In this situation, work is done. A boy pulls a car and the car moves through a distance. The boy has exerted a force on the car and it is displaced. Therefore, work is done.

2. Lift a book through a height. To do this you must apply force. The book rises up. There is a force applied to the book and the book has moved. Hence, work is done. A closer look at the above situations reveals that two conditions need to be satisfied for work to be done:

(i) A force should act on an object.
(ii) The object must be displaced.

If any one of the above conditions does not exist, work is not done. This is the way we view work in science.

Work done by a Constant Force

How is work defined in science? To understand this, we shall first consider the case when the force is acting in the direction of displacement. Let a constant force F act on an object. Let the object be displaced through a distance, d in the direction of the force. Let W be the work done.

We define work to be equal to the product of the force and displacement.

W = F x d

Let us label it as equation 1. Thus, work done by a force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force. Work has only magnitude and no direction.

In Equation 1, if F = 1 N and d = 1 m then the work done by the force will be 1 Nm.

Here the unit of work is newton meter (Nm) or joule (J).

Thus 1 J is the amount of work done on an object when a force of 1 N displaces it by 1 m along the line of action of the force.

Unit of Work

The SI unit of work is the joule (J).

If we look at equation 1 carefully, can you tell what is the work done when the force on the object is zero, or What would be the work done when the displacement of the object is zero?

You will find that in both cases, that work done is zero.

In another scenario, the force and the displacement are in the same direction, for example, a boy pulling a toy car parallel to the ground. The boy has exerted a force in the direction of displacement of the car. In this situation, the work done will be equal to the product of the force and displacement. In such situations, the work done by the force is taken as positive.

In this blog, you have got a grasp of what is work energy and power and learned their formulae and SI units. You have also understood the difference between work, energy, and power.

Read More- Kinetic Energy and Potential Energy: Definition, Derivation, and Examples