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SLMtitle.png Work, Power and Energy

Chapter Outline


  Meaning of Work, Power, Type of Energy
            Meaning of Work
            Concept of Power
            Type of Energy

SLMinto.png Introduction

The concept of Work, Power and Energy are very related and important factor of every human life. We are needed to understand of this concept. The work done by the force on the piratical as it moves some given distance is defined as the product of the force and the displacement. The amount of work done expended per unit time is called power.

SLMobj.png Learning Objectives
After reading this chapter, you are expected to learn about:

  • Explain the meaning of work
  • Explain the Meaning of Power
  • Explain the Type of Power


Whit is work To introduce the definition of work done by a force, We begin with the simple cause of motion along the line of motion, Consider a practical moving along a straight line say, The X axis, and suppose that a constant force F, directed along the same straight line, acts on the practical. For example, the practical might be a stalled automobile that the work done by the force for the practical as it moves some given distance S is define as the produce of the force and the displacement.

W = F.S = FSCos a Where a is the angle between the force F and displacement S. Work is a scalar quantity. The unit of work is

[W] = [F] [S] In metric system, unit of work is joule.

[W] = 1 joule = 1. m 1Joule =

In CGS system, unit of work is erg. Relation between the units of work is 1 Joule = 1N.m=105 D. 102 cm =107 ergs

What is Power :

The amount of work done energy expended per unit time is called Power The algebraic expression for power is P= The SI unit of power is called the watt (W) and it is defined as rate of transfer of energy of 1 Joule per second. Thus 1 Watt = 1 Joule/sec = 107 ergs/s. Larger units used are the kilowatt (KW) and them megawatt (MW). 1KW= 1000 W 1MW= 1000000W


Type of energy :

Kinetic Energy In every language, Energy means capacity for activities and hard work, Likewise, In physics energy is capacity for performing work Energy is “Stored” work, which can be converted in to actual work under suitable condition. For instance, a body in motion, such as a spending arrow, has energy of motion, or kinetic energy. This energy will be converted into work when the arrow strikes a target. A high-speed arrow has deeper penetration and delivers a large amount of work to the target.

When a force positive work on a body initially at rest, the kinetic energy of the body increase. The body than has a capacity to do work if the moving body subsequently is allowed to push against some obstacle, than this obstacle doses negative work on the body and simultaneously the body dose positive work on the obstacle, when the body dose work, its Kinetic energy decrease.

Potential energy

The gravitational potential energy represents the capacity of a body to do work by virtue of its height above the surface of this earth. When we lift a body to some height above the surface, we have to work against gravity, and we thereby store work in the body.

Chemical energy and Nuclear energy

Chemical energy and Nuclear energy are two other forms of energy. The former is kinetic & potential energy of the electrons within the atoms; the latter is kinetic & potential energy of the protons and neutrons within the nuclei. As in the case of heat, whether these are to be regarded as new forms of energy depends on the point of view.

SLMsum.png Results

SLMkp.png Key Points

The key points of this chapter are as follows:

SLMgloss1.png Glossary

SLMtest1.png Practice Test

1.1 Multiple Choice Questions (Give the tick)

1. The physical meaning of energy is a) Capacity for motion b) Capacity for doing work c) Energy is expended per unit time d) None of the above

2. The Kinetic energy represents a) Capacity of work by virtue of speed b) Capacity of work due to potential c) Energy is expended per unit time d) None of the above

Short Question

a) What do you mean by work b) What is energy