The intuitive meaning of work is quite Different from the scientific definition of Work . In everyday activity , the term ‘work’ is used equally for mental and

physical work involving muscular force.

In physics , the term work is used in special technical sense and has a much more precise definition .

DEFINITION When force is acted on a body and the

body get displaced through a distance then work is said to be done .

There are two conditions that must be

satisfied in work done by a body .- A force is applied on the object .- The object be displaced from its

original position.

Mathematically Work is defined as the product of force acting on the body and

displacement is produced in the body . Formula of work is :

W = FScosθ

θ (Angle in degree) COSθ O 1 90 0 180 -1

CASE 1 When the direction of force and displacement are

same . we know W = FScosθ (θ = 0 [in degree] ) W =FScos180 W =FS* 1 W =FS Example- when a body is dropped from a certain

height.

When force and displacement are in opposite direction.

we know w =FScosθ [in this case θ = 180(in

degree) ] W =FScos180 W =Fs*-1 W =-FS Example – When a body is thrown

vertically upward .

When force and displacement are perpendicular to each other . [ in this case

θ = 90(in degree) ] . Therefore W = FScos90 W = FS* 0 W = 0 Example – The work done by a porter on

the platform is 0 .

SI Unit SI unit of work = SI unit of force * SI unit

of displacement Joule (J) = N * m J = Nm

CGS Unit of work = CGS unit of force * CGS unit

displacement erg = dyne * cm erg = dynecm

We know 1j =1N * 1m 1j = 100000 dyne * 100

cm 1j = 10000000 erg

1 kilo Joule = 1000 Joule

1 Mega Joule =1000000 Joule

Energy of an object is defined as its capacity for doing work and it is measured

by the total quantity of work it can do. OR Ability to do work is called energy .

SI unit of energy is same as the SI unit of work. i.e. joule (J).

There are many types of energy but Kinetic energy and Potential energy have mathematical .

Solar Energy Heat Energy Light Energy Chemical Energy Wind Energy Hydro Energy Sound Energy Electric Energy Magnetic Energy Tidal Energy Nuclear Energy Mechanical Energy

Solar Energy The energy radiated

by the sun is called solar energy used in photosynthesis .

Heat Energy When energy

released by gas , oil , petroleum products is called heat energy .

Light Energy Energy which

produce sensation of vision.

Chemical Energy Energy which is

produced by fuels , chemicals etc.

Wind Energy Energy produced by

moving air .

Hydro Energy The energy

produced by flowing water is called hydro energy.

Sound Energy Energy which

produced by the vibration of object and produced sensation of hearing .

Electric Energy Energy Produced by

flow of charge .

Magnetic Energy Energy produced by

magnet .

Tidal Energy Energy produced by

high and low tides .

Kinetic Energy The energy in a

body by virtue of its motion is called Kinetic energy .

Potential Energy The energy in an

object by virtue of its position or configuration is called its potential energy .

Nuclear Energy The energy which

produced by nuclear reactions is called nuclear energy .

Mechanical Energy The sum of kinetic

and potential energy is called mechanical energy .

Mathematical definition of kinetic energy is equal to half the product of mass and square of velocity .

Mathematically potential energy is

equal to the product of mass , acceleration due to gravity and height .

P.E = M * g * H

The conversion of energy from one form

of energy to another form of energy is called energy transformation .

According to law of conservation of energy can neither be created nor be destroyed only it can be destroyed from one form of energy to another form of energy .

Rate of doing work done is called power .

OR Work done per unit is called power . W =Work Done T = Time P = W / T

si unit of power = si unit of wok / si unit time

W = J /SI Unit of power is Watt [ W] and is

named in the honor of James Watt .

Practical unit of power or a unit which is exclusively used in engineering or in automobiles is called horse power (hp) .

1 hp = 746w

It is defined as the ratio of total workdone by the body to the total time taken by the body

AP = Total workdone / Total time

Commercial unit of electric energy is Kilowatt-Hour (KWH).

Commercial Unit of electric energy i.e. KWH is used in household industries for measuring electric energy consumption .