• Physics
• Chemistry
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• Astronomy and Geology
• Environmental Science

## Subject Contents

### Chapters

• Physics
• Chemistry
• Biology
• Astronomy and Geology
• Environmental Science

# Work, Energy & Power

Work:-

Work is said to be done when force applied on a body makes a body to move some distance in the direction of applied force.

Mathematically, it is calculated by the given formula.

i.e. Work = Force × distance

or, w = F × d

or w = m × g × d

Where,

m = Mass of the body

g = 9.8m/s2 ( it is the value of acceleration due to gravity of the earth)

d = Distance moved by the body.

W = Work done

Unit of work:-

SI unit of work is joule (J) and CGS unit of work is erg.

Where,

1 N = 1,00,00,000 ergs

Or, 1 N = 107 ergs.

1 Joule work :-

When 1 Newton (N) force is able to displace a body through the distance of 1meter (m) in the direction of force then this work is called 1 joule of work.

W = F × d

1 J = 1 N × 1 m

Conditions for the work done:-

The amount of work done by a body depends on the following two factors:-

• The magnitude of force should be applied on a body.
• Body should travel at least some distance after the application of force.

Types of work:-

On the basis of nature, there are two types of works. They are:-

(i) Work against gravity (ii) Work against friction.

Work against gravity:-

When force is applied in the opposite direction to gravity while doing the work then this is called work against gravity.

For example:-

• Pulling water from the well.
• Liftingsomething upward by crane.
• Throwing a stone in the sky.
• Pulling water at the roof of the building. etc

Work against friction:-

When force is applied in the opposite direction to friction then this is called work is called work against friction.

For example:-

• Running vehicle on the road.
• Pushing a bag on the bench.
• Pulling a stone on the ground.

Energy:-

Energy of a body is defined as the capacity or ability to do the work.

Or

Capacity of doing work is called as energy.

Unit of energy:-

Energy is measured in the unit of joule (J) in SI unit.

Whereas it is also be measured in the other units like Kilo joule (KJ),Mega joule (MJ). etc.

Types of energy:-

There are many forms of energy. Among them some are as follows:-

• Mechanical energy.
• Heat energy.
• Light energy.
• Sound energy.
• Chemical energy.
• Magnetic energy.
• Nuclear energy.
• Electrical energy.

Mechanical Energy:-

The energy that is produced due to position of rest or motion of a body is called mechanical energy.

It has two types. They are:-

(i) Potential energy

(ii) Kinetic energy.

• Potential Energy:-

The energy that is produced due to rest body is calledpotential energy.

Sources of potential energy are:-

• Stretched rubber,
• Leg lifted to kick a ball,
• A stone raised at some height.
• Water stored in a dam etc.
• Stretched catapult.
• Kinetic Energy:-

The energy that is produced by a moving body is called kinetic energy.

Sources of kinetic energy are:-

• Moving wind
• Flying bird.
• Running vehicles
• Rolling a stone from the cliff.
• Flowing water in the river
• Fired bullet etc.

Differences between potential energy and kinetic energy

Heat Energy:-

Heat is a form of energy that gives the sensation of warmth to our body.

Or

Heat is defined as the sum of kinetic energy of all the molecules present in a body.

Heat energy is produced from a body due to molecular vibration.

Sources of heat energy are:-

• Sun.
• Burning coal.
• Electric heater
• Burning firewood. etc

Light Energy:-

Light is such form of energy that gives the sensation of vision to our eyes.

It makes the things visible. It is produced from a body having very high surface temperature.

Sources of light energy are:-

• Glowing lantern
• Burning candle
• Sun
• Diyo
• Tuki
• Moon.Etc

Electrical Energy:-

The energy that is produced due to charged body is called electrical energy.

It has two types, they are:-

(i) Current electricity.

(ii) Static electricity.

(i) Current electricity:-

The energy that is produced due to flow of electrons in a conducting wire is called current electricity.

It is produced in a conducting body.

For Example:-

• Running fan due to electricity.
• Operating TV due to electricity.
• Operating radio due to electricity.

(ii) Static electricity:-

The energy that is produced on a body due to unequal number of electrons and protons is called static electricity.

It is produced in an insulating body.

For Example:-

• Attraction of pieces of papers by a rubbed comb on hair.

Chemical Energy:-

The energy that is present in a chemical substance is called chemical energy. It is produced from the body after chemical reaction.

Sources of chemical energy are:-

• Diesel
• Rice
• LPG gas cylinder. etc.

Nuclear Energy:-

The energy that is produced on decomposition of a heavy nucleus or combination of lighter nuclei is called nuclear energy.

Nuclear energy is produced by two different ways. They are: -

(i) Nuclear fusion.

(ii) Nuclear fission

(i) Nuclear fusion :-

The process of combination of two or more than two lighter nuclei to form a heavy nucleus is called nuclear fusion.

It is an uncontrolled chain reaction. Hydrogen bomb is made in this process.

(ii) Nuclear fission :-

The process of decomposition of a heavy nucleus into two or more than two lighter nuclei is called nuclear fission reaction.

It is a controlled chain reaction. Atom bomb is made in this method.

Differences between nuclear fusion and nuclear fission reaction.

Magnetic Energy:-

The energy that is produced by a magnet on magnetic materials is called magnetic energy.

For Example :-

• Attraction of iron by a magnet.

Sound Energy:-

The energy that gives the sensation of hearing to our ears is called sound.

It is also produced due to molecular vibrations.

Sources of sound energy are:-

• Bell
• Guitar
• Television. etc.

Differences between work and energy

Transformation of energy:-

*The process of changing of one form of energy to another form of energy is called transformation of energy.

Some examples of energy conservation are:-

• Bulb converts electrical energy in to light energy.
• Radio converts electrical energy in to sound energy.
• Fan converts electrical energy in to kinetic energy.
• Human body converts chemical energy in to mechanical energy.
• Microphone converts electrical energy into sound energy.

Power

Rate of doing work of a body is called power.

Or,

It is also defined as the rate of transformation of energy.

Mathematically, power of a body is calculated by:-

$$Power = \text"Work Done" / \text"Time Taken"$$

$$or, Power = \text"W" / \text"t"$$

$$or, Power = \text"F x d" / \text"t"$$

$$or, Power = \text"m x g x d" / \text"t"$$

Where,

W = Work done.

t = Time taken.

F = Applied force.

d = distance travelled.

m = mass of a body.

g = (9.8m/s2) is the value of acceleration due to gravity of the earth.

P = Power of a body.

Unit of Power:-

Power of a body is measured in theunit of watt (W) in SI system.

Similarly, It is also measured in the units like kilowatt (kW),

megawatt (MW),horse power (hp) etc.

Where,

1 Kilo watt = 1,000 W

1 Mega watt= 1,000 KW

Or,

1 Mega watt = 10,00,000 W

1 horse power = 746 W.

1 horse power = 750 W (approx.)

1 watt power:-

When 1 joule of work is done in 1 second then this is called 1 watt power.

Power of an electric lamp is 100 watt. What does it mean?

It means that, that electric lamp can convert 100 joules of electrical energy in to heat and light energy in 1 second.

17. Differences between work and power.

The End

Some questions for practice

- What is work? What is its formula to calculate it?
- What are SI unit and CGS unit of work?
- Define 1 joule of work.
- What is the relation between watt and horsepower?
- What is work against gravity and work against friction? Give 1 example of each.
- What is energy? Mention its SI unit.
- Differentiate between kinetic and potential energy.
- What is sound? Give any three examples.
- Define mechanical energy.
- Define heat, chemical and magnetic energy.
- What is nuclear energy? Differentiate between nuclear fusion and nuclear fission.
- What do you mean by transformation of energy?
- Define power.
- What is 1watt power?
- Give some example of transformation of energy in our daily life


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This content is contributed by:

Dipak Dangi