“Physics for everyone”

Understanding Nature

Vedang Sati

Introduction

Physics is an interesting subject but it becomes even more amazing when one recognizes its physical

importance. The real joy of physics is attained by living it. This book Physics for everyone comes

with the perspective to enlighten every human mind with the love of physics. If you know the rules,

you can enjoy it too!

Each chapter is easy to read and follow. Your understanding is complemented by numerous real-life

examples. Conceptual problems and activities are given at the end of each chapter. Thus, you can be

sure that you are going to learn a great deal of physics with a lot of curiosity about your immediate

surroundings. This book is not intended to physics students. This book tries to allure all people

toward the laws of nature. Don’t worry about mathematics. Physics is about observing nature and

enjoying its rules and regulations. All that you need is a desire to learn and a bit of curiosity to look

around!

What do you need?

You need your eyes wide open. Look around yourself with a bit more passion and a bit more

curiosity. This is physics for everyone!

What will you learn?

You will learn about physics in detail and believe me, you will learn it all very easily! You will

learn about motion, gravity, heat and energy, about light and electromagnetism, about atoms, about the

universe and a lot of amazing physical phenomena!

Why do you need to know it?

Your immediate surroundings are governed by the laws of physics. The devices and technology that

you use are because of physics. Our discussion will be very informal, as if we were talking to each

other. You will have to know the rules before you start loving physics.

Get ready to learn about how stars make light, how light reflects and refracts, how

atomic bombs are made, how lightning occurs and how we use physics in our daily

lives!

Vedang Sati

Contents

1. Understanding Motion

2. Understanding Gravity

3. Understanding Heat

4. Understanding Energy

5. Understanding Light

6. Understating Atoms

7. Understanding the universe

8. Understanding Physics

Chapter 1

Understanding Motion

Motion is a part of our everyday lives. You often hear people saying how fast a formula one car

moves. They appreciate a physical quantity called speed. Speed is how fast an object moves. When

bodies move, they have speeds. For example, if a body covers 100 meters in 10 seconds, its speed

will be 10 meters per second. But here we get it wrong. We are actually talking about the average

speed in this case.

Suppose Allen travels from city A to city B in just 2 hours, travelling a distance of 500 kilometers.

His average speed is 250 kilometers every hour, thus covering 500 in 2 hours. But this gives no

information about journey at every instant. We do not know about his instantaneous speed.

Instantaneous speed and average speed are two different quantities. While average speed sums up the

journey, instantaneous speed gives the speed at every moment. In our day to day life, we talk about

speed when we want to tell how fast it moves. Our very notion of speed is the distance covered by an

object within some time interval. This is speed.

Many of you may have heard about acceleration. If you are very interested in cars, especially super

cars, you always read about the acceleration of the car. Some cars can accelerate from 0 meters per

second to 100 meters per second in just three seconds. What does this suggest about the car? Suppose

the car starts with a speed of zero, then it can pick up the speed of 100 in just three seconds. This is

what acceleration means. Acceleration is the rate of change of speeds. Acceleration tells us how

quickly the car switches between two speeds.

Our ancestors have tried to explain motion. Many failed and many survived the test of nature. It was

Aristotle who began the discussion. What did Aristotle suggest? He said that bodies moved because

they were acted upon by a force. Everyone could see that when they kicked a ball, it moved. Another

of Aristotle’s statements was that bodies stopped moving when they get tired. This statement, although

stupid, was accepted by people – believing in Aristotle’s authority.

But Galileo was a fine man. He wanted to test Aristotle. He wanted to question each of Aristotle’s

postulates. The Greek philosopher Aristotle had once said, if a feather and a stone fell at the same

time from some height, the stone would hit the ground first because of greater attraction to the

earth. According to Aristotle, heavier the body, more the pull will be.

Galileo started from scratch. He asked himself: W hy do bodies move and why do they stop? Galileo

came up with good answers. He introduced a new term called inertia. Galileo told people that each

body with mass has inertia. Inertia can be compared with laziness – the more the mass, the lazier the

body becomes. It is the tendency to resist changes. A heavier body has greater inertia due to greater

mass, thus it will resist any change to its state. If this body is at rest, it would tend to remain at rest

forever. If it is in motion, it will tend to remain in motion forever. Every object has inertia, it just so

happens that an object with more mass has more inertia. Look at the image following this paragraph.

You pull out one of the books, the rest of the books resist change in their states, they tend to remain on

the top of the bottom two books, and they thus fall down. But how did Galileo find inertia in the first

place? How did he guess its existence?

Galileo worked with rolling bodies. He worked with pebbles, round stones and inclined planes. He

rolled down marbles from one plane to another and observed the height reached by the marble on the

second plane. This is reflected in the image below.

He found that when he released a marble from height H from the first inclined plane, the ball tries to

reach the same height H on the second inclined plane. He was not convinced. He used smoother

inclined planes and better rolling marbles. He did the experiments again and he found that the marble

reached the same heights. The next part of his experiment was to reduce the incline of the second

plane as shown below.

The marble moved further distance in order to reach the same height H from where it was released.

You will learn in the chapter Understanding Energy that since energy is conserved, the marble

should reach the same height H. Ultimately, Galileo reduced the incline of the second plane to zero. In

this way, he imagined that if the plane surface were frictionless (actually friction was first identified

by Galileo, Aristotle knew nothing about frictional forces – these forces oppose motion, like air

drag, ground friction, etc.) the ball should roll on and on, forever, in order to reach the same height!

Thus he found that an object at rest tends to remain at rest and an object in motion tends to remain in

motion unless and until, an external agency, an external force causes it to act otherwise. Believe me,

this experiment is very beautiful and I have performed this experiment at home. I found results

agreeing with Galileo’s inertia. The beauty of physics is that Newton used Galileo’s discoveries and

converted them into three laws of motion.

Isaac Newton was an English natural philosopher. The first encounter with physics was the fall of an

apple. An apple fell and Newton asked why. That simple question led him to uncover gravitation. He

found that the same force with which earth had attracted apple, kept earth around the sun! In fact,

Newton found that every object in the universe attracted every other object with a mutual force.

Gravity was born. We will discuss about gravity in the next chapter. In this chapter, we will see how

Newton explained motion of bodies.

The first law of motion has already been discussed. An object at rest remains at rest forever unless

any external act, causes it to act otherwise. A body in motion always remains in uniform motion

unless and until an external act causes any change. So far, so good – the object is either at zero

velocity or uniform velocity. But Newton’s second law shows us what happens when an external

force does act on the body.

The body starts to accelerate. Force causes change in speeds. Will the body move without any force?

Yes, a body can move without any force acting on it – but it would not change its speed until acted

upon by a force, a net force.

Last but not the least, Newton’s third law of motion states that every action has an equal and opposite

reaction. If you push on a wall, the wall pushed back at you. If you kick a ball, you apply force on the

ball, in return, the ball also applied a force on your leg – instantaneously so that there is an action-

reaction pair. You will find that action and reaction occur on two different bodies.

For example: An object is kept on a table. There are two forces which are acting on this object.

These two forces which are impressed on the object will have their reactions too – according to the

third law of motion. The first of these forces is earth’s pull – acting downward (object’s weight).

Earth is pulling this object down! But this object stays where it is – on the table! Why? This is

because of the second force being impressed on it. The second force is due to the table – which is an

upward force. We know the magnitude of this upward force exerted by the table – it should equal the

weight of the object so as to keep the net force zero and to keep the object where it is. You can see

the diagram below – which shows the forces impressed on the object. But the two forces have their

reactions too. Earth pulls the object down, but in return, object pulls the earth upward! This is the

first action-reaction pair. The second force which was due to the table, also has a reaction. This

object exerts a reaction force on the table too! These forces are shown in the diagram below – these

are the forces exerted by the object. Two forces were impressed on the object and two forces were

exerted by the object itself, thus forming two action-reaction pairs as shown below. You have a clear

understanding of forces now. You know the laws of motion.

But you still don’t know most of the things about motion. We want to ask the following questions:

1. Why do objects move?

2. What happens when a body collides with another body?

3. Why do objects in motion stop?

4. And what exactly motion is?

Let me tell you of what we have been doing so far. We have got only an idea of what motion is. We

define motion as movement, right? But there is more to it, as we shall see. We also discussed about

how Galileo challenged Aristotle and how he experimented with rolling bodies. We talked about

inertia but there is a deeper meaning to it, which we have to understand.

Let us answer the first question. Why do objects move? If you were Aristotle, you would say, objects

move because of the force implied on them. Then, you would be wrong! Force is not required at all

to keep a body moving. A force is required to change how a body is moving – it can speed it up or

slow it down. So why do objects move? The answer is inertia. Suppose that you are travelling in a

car at 30 meters per second. Suddenly, brakes were applied and the car screeches and stops. You

tend to fall forward. This is why there are airbags in your car to keep you safe. What if you were

travelling at 90 meters per second and there were no airbags in your old car!

The next question is: What happens when a body collides with another body? To answer this

question, we have to understand a new physical quantity. You have heard about this and you use it in

your life. This is called momentum. “Oh I wish I could keep the momentum on!” – This is one of the

many sentences that we say. What is momentum? Believe me or not, momentum is a very physical

quantity, one that has enormous physical significance. You get the idea of momentum when a body

collides with another body. What happens when a moving ball collides with a stationary ball? You

see that the ball that was once stationary also starts to move. Why does it move?

It moves because of transfer of momentum. Momentum is a quantity that an object has and which it can

transfer to another body. You cannot transfer speed or acceleration like that – all that you can do is

transfer momentum and see what happens. A moving body has momentum – only a moving body. A

body which is kept on a table has zero momentum. It is not moving. A boy running at 5 steps per

second has momentum too. A truck moving at 30 meters per second has momentum too.

So we were talking about collisions. What would be the consequence of the collision of a truck and a

bicycle? Suppose that you are riding a bicycle, at some normal speed. I give you two options, out of

which you have to choose one. You have no other choice but to choose out of these two options: You

either collide with a car travelling at 20 meters per second or with a fully-loaded truck moving at the

same speed. What will you choose? Obviously, if you are clever enough (and if you definitely have

no other option left) you will choose to collide with the car. Why? It is obvious that you would get

more hurt – or you would die – if you chose to collide with that heavily loaded truck. Two objects

with different masses moving at the same speed have different momenta. The one with greater mass is

the one with greater momentum. Thus, more momentum would be transferred to you and your puny

bicycle. You would be severely injured. You now have the idea of what momentum is and in this

way, we have answered the second question.

The third question, however, is a bit trickier. Why do objects stop moving? Aristotle had been fooling

around with people by saying that objects stopped because they got tired. Do tennis balls get tired?

Actually, he was fooling around with his own mind. It was Galileo who fully realised why objects in

motion stopped. Galileo introduced a new term – Friction. Friction is a force, an opposing force. An

object moves on a marbled floor. That same object now moves on a rough floor, like that of a

playground, with tall grass. It is obvious that it would stop quickly on the rough surface. Roll a ball

and you will find the answer.

What exactly motion is? This is the last question that we need to answer to fully understand motion.

Haven’t we done enough? We know that whenever an object changes its position with time, it moves.

It moves with certain speed and if it changes its speed, it is accelerating. We found that to accelerate,

forces have to be applied. Yet, we do not know the most important thing about motion. Do not worry,

I am going to give you a hint. So here is the hint: Aristotle saw that the sun, the moon, the stars and

the planets were crossing earth’s sky. They were seen moving, yet he did not see earth to be

moving. Earth seemed to be static. Thus Aristotle concluded that earth was stationary and that it

was the centre of the universe and every other heavenly body revolved around the majestic earth.

Did you get the hint? Motion is relative. It was Galileo who realised that motion was relative.

Actually earth is moving around the sun. So why don’t we see it moving? This is because all objects

on earth (including earth itself) are moving at the same speed. The pen on your study table, the books

on the bed and your TV are static relative to you (you are sitting on a chair) but if someone on moon

observed you, he would see you moving – moving at the same speed at which earth is moving!

So if you get a chance, try to move abreast a bus. You move in your car and the bus moves side by

side. You see the bus and the bus sees you. Match the speeds and you feel no motion relative to bus. I

get amazed whenever I practice this! I get amazed by the relativity of motion. For someone inside the

bus, you are stationary, since your speed matches that of the bus. But for someone standing on the

ground, you are in motion – only because there is a difference in speeds.

This is motion.

Chapter 2

Understanding Gravity

You are always acted upon by a force called gravity. Gravitation is a universal force and every

object in the universe attracts every other body with a force proportional to the product of their

masses. The force falls off as the distance increases. How do you know that you are under earth’s

gravitational pull? Even though you cannot directly see gravity, you can still feel it. Jump up and you

will get down. You should not try to fly because you cannot. Gravity pulls you down.

But nature has some boundaries. Earth has a limited gravity. We have learned to overcome

gravitational pull and there is a special speed with which if we travel, we could fly into space. If you

throw a stone straight up, gravity will eventually bring it down. But if you have enough power to

throw this stone at a special speed, and let us assume that the stone continues to travel at the same

speed, the stone would fly out into space. This special speed is called escape speed, because it can

be used to escape earth – its value is 11.2 km / s directed upward.

We are here to understand gravity. What is gravity? How did we get to know about this force and

how did we understand its behavior? It turns out that there are 5 heroes of gravity. They are

Copernicus, Galileo, Kepler, Newton and Einstein. They have led to our understanding of the

universe as well as gravity. So let us begin the story of gravity.

It was Nicholas Copernicus, a Polish priest who predicted that sun was the centre and not the earth.

Before him, everybody had believed on the geo-centric model of solar system, i.e. earth was the

centre of the universe. This earth-centred model was supported and firmly established by Aristotle

and Ptolemy. Thus, it was a daring move to challenge the old theory. Copernicus was punished for his

bold proposition.

Copernicus was unlucky because he did not have enough data to explain what he wanted to say. The

next hero was Johannes Kepler. He was a German astronomer and mathematician who was keenly

interested in geometry and wanted to use geometry to explain celestial motion. He used Tycho

Brahe’s data – another astronomer of his day and deduced three laws of planetary motion which are

called Kepler’s laws of planetary motion. Kepler had always supported Copernican theory – every

object revolved around the sun. The most important law, however, was that of the shape of the orbits.

Copernicus had used circular orbits in his theoretical model but when matched with Brahe’s data,

only elliptical orbits fit the best. An ellipse is an elongated circle. A circle has a unique centre – on

the other hand, an ellipse has two foci. You can think that circle is an ellipse in which distance

between the two foci is 0, while an ellipse is an elongated circle in which the two foci are separated

by some distance. The figure below shows you an ellipse and a circle.

It was Galileo who was the first to realise the existence of a mutual force between heavenly bodies

because he found tiny bodies circling the planet Jupiter. He therefore modified the Copernican theory

by proposing that not every object had to directly revolve around the sun. Galileo also confirmed

the Copernican theory because he had proof. He had a special instrument called telescope with which

he became the first man to peep into space. He discovered Saturn’s rings and was astonished at the

beauty of Saturn. Galileo paved the way for Newton to realise the existence of gravity.

Isaac Newton was an extraordinary kid. He was curious about nature, about plants and animals. He

soon realised his interest in mathematics and physics. This story is very interesting. He was once

sitting under a tree and was accompanied by an apple fall. An apple fell and a quick question popped

up: Why did the apple fall down? Why didn’t it go up? These questions haunted Newton for several

years until he came up with an answer. As he fought for his answers, he came up with a new branch of

mathematics called calculus. He used his imagination and his knowledge of mathematics to unlock a

secret force – the force of gravity. Gravity was born and Newton explained that every object attracted

every other within the universe with a mutual force.

We have thus studied about the four heroes so far. One more is left. But before that, we must

encounter special and amazing characteristics of gravity. So let us first examine the fall of an apple.

When an apple falls, it is pulled by the earth. This force is F, it just so happens that the apple also

pulls the earth with the same force F but directed oppositely. Thus, earth pulls the apple down, and

the apple pulls the earth upward – very much in agreement with Newton’s third law of motion. We

see only the apple moving and not the earth because we know that the same force is acting on the tiny

apple and the same force is acting on the massive earth. If you try to move a bicycle with a force F

and you use the same force to move a mountain, you would hardly succeed. In our example, we have

an apple, which is less massive than a bicycle and we have earth, more massive than any mountain.

So we won’t see the earth moving, we would see the apple fall down. This is obvious but now you

also know why it should be obvious.

The second thing that we must know about is weight. Mass and weight are two different quantities.

Your weight is the direct result of earth’s gravitation. If you were on the moon, you would weigh very

less than what you weigh on earth but if you were on Jupiter, you would weigh more than the double

than what you weigh on earth. Thus, weight is always perceived and it changes from place to place.

We must also know about rockets which are able to escape earth’s gravity. In the previous chapter,

we looked at Newton’s three laws of motion. Actually, rockets work on Newton’s third law – the law

of action and reaction. A rocket uses a mixture of gases as its fuel. These gases are highly

compressed, i.e. they are under enormous pressure. When there is takeoff, all these pressurized gases

escape the nozzle. They apply an enormous force on the launch pad, i.e. on earth and in return earth

pushed the rocket upward. This is an excellent example of Newton’s laws and this allows it to escape

earth’s gravity. Not every rocket can escape earth – only the powerful ones are capable to do so.

The last hero of gravity is Albert Einstein who managed to explain how gravity actually worked. He

explained that the universe was composed of a special fabric. Let us suppose this to be made of

rubber. A trampoline is a good example. If you put a massive object on this fabric, there is a

depression. So if you stand on a trampoline, your feet produce a depression on the rubber sheet.

Einstein stated that this was the case with masses in space. Planets, stars and all other bodies produce

depression in the fabric of the universe. This depression would be greater if the mass would increase,

thus, sun would produce the greatest depression in our solar system. So you stand on a trampoline, in

our analogy, you are the sun. Now I come around, I take out a small iron ball from my pocket, just

about the size of a tennis ball – but it is made of iron – it is very dense. I put it very carefully around

your feet. What will happen? Clearly, this ball will try to fall toward your feet. In doing so, it will

revolve around you. This is the truth – Einstein stated that all bodies in our solar system fell into the

sun’s depression. All that we have discussed about Einstein’s theory has been carefully shown in the

diagram below. It shows a planet creating its depression. You can now see where gravitation comes

from – it comes directly from the curved depressions created by the masses. Thus, we have

understood the five heroes of gravity and their stories.

Here, earth is creating a depression on the fabric of cosmos

Gravitation as we know it, is a force. If you want to know more about the stories of Galileo, Newton

and much more about how Einstein corrected Newtonian theory of gravity, you should try this book

below. It is called Gravitation: A crucial breakthrough in Physics – available on Amazon

Revision 1

1. What is motion? Give examples of a moving body. Also give examples of a body which is at

rest. Always consider relativity of motion.

2. State and explain the three laws of motion as given by Newton.

3. Take a pencil and a paper. Hold them at the same height in your hands and then drop them

simultaneously. What do you observe? What hits the floor before? Now crumble the paper

and make it like a ball. Repeat the experiment. What do you observe this time?

4. A man is trying to push a car with a force of 1000 Newton but the car is still not moving.

Eventually, as he continues to push, the car finally moved. He noted that the force he had to

apply to move the car was 1500 Newton. What was stopping the car?

5. A box is kept on a table. How many forces are acting on this box? If the box is at rest, what

can you say about these forces?

6. Take a balloon and blow in air. Make it big. You have now filled air inside – the molecules

of air are now moving around randomly. Now leave it to fly. The balloon will fly around.

Why do you think it flies?

7. A tennis ball and a leather ball (both of the same size) are dropped from the same height on

a muddy ground. Which would create a deeper depression on this ground?

8. Now you drop a tennis ball from height 20 m and drop a leather ball from 10m at the same

time. They are of the same size. Which would create a greater depression on the muddy

ground?

9. Why do planets revolve around the sun? Which force exists between all bodies?

10. Earth’s gravitational acceleration is close to 10 m/s2 and your mass is 30 kg. What will be

your weight on earth? If moon’s gravity is only 1/6th times that of earth, what will be your

weight on moon?

11. Who were the five heroes of gravity? Who is your favourite? Why?

12. Write different things that you see so that you can be sure that gravity exists.

13. A bus and a car are moving side by side. Both are moving at the same speed. You stand on

earth, do you measure their speeds to be zero?

14. You get on the bus. The driver of the car decided to overtake the bus. He drives the car at

twice the speed as that of the bus. What speed do you see?

Chapter 3

Understanding Heat

Heat is a form of energy. When you bask under the sun, you feel its heat, you get warm. Sun is

providing you some energy which your body uses to maintain a temperature good enough to keep you

warm. What is temperature? Take any two bodies, one sees that one of the bodies is relatively cooler

than the other. Consider earth and sun. Sun is hotter than our earth. Take a more familiar example:

Take a hot cup of tea and touch it with your hands. Now before touching, your hand was cooler. But

slowly, as you keep touching the hot cup, your hand starts to get hotter than it was before.

Sometimes, we are in hurry. I am prone to this behavior too. So, sometimes, when the food is still hot,

I (without knowing the temperature of the chapattis) take them in. My mouth burns and I look for

water. But then, I realise that slowly as I keep eating hot food, temperature of my mouth and that of the

food will equal. I mean to say that when I had not taken any hot food inside my mouth, it was at

relatively lower temperature than the food. Thus, when hot food was taken in, my mouth could not

bear the new increase in temperature. It takes time for the difference to decrease.

So I have defined temperature, but indirectly. Temperature is the measure of how hot or how cold a

body is. It is not heat. When you say: “This body has high temperature” – you are wrong. This is

because temperature is relative. A cup of tea is hot only relative to your hand. It is not hot relative to

sun. I hope you understand the difference. So what is heat?

I say it again. Heat is a form of energy. But why does heat exist at all? Where does it come from?

Why is one body hotter than the other? A good answer comes to my mind. When there is a difference

in temperature between two bodies, heat transfer occurs between them. Since the body that is hotter of

the two has excess of heat, it will want to decrease its energy and become stable. The other body will

gain some heat and become hotter than it was before. The transfer occurs until there is equilibrium.

What is equilibrium? It is a state of equality. You keep a hot cup of tea on your study table. But some

way or other, you forget to consume it. The cup does not care for you. It will lose heat. The

surrounding just close to the cup is cooler relatively. Nature does not like this, nature wants harmony.

Eventually, your hot cup of coffee will get cooler. It cannot store heat forever!

What are we trying to talk about? So far, we know that heat is a form of energy. Temperature is a

degree of measure of hotness or coldness and that heat transfers from a hot body to a cold body. We

are yet to talk about equilibrium.

Take a tank. Divide this tank into two parts. Fill one of the halves completely with water. The other

half should remain empty. Now remove the partition between the two halves. What will happen? You

say that it is obvious that the water from the one half will distribute equally between the two. This is

obvious, isn’t it? With heat, this is obvious too.

Now think about particles. Think about gases. Take a tank and it has air inside. Air has lots of small

particles that we cannot see. These particles or atoms move around randomly. Why do they move?

They have thermal energy. But if we heat this tank, we provide the energy to the tank. The atoms

would speed up. Their thermal energy will increase.

What am I trying to say? You may ask. I am trying to show you how the world works. You heat an ice

cube. It will turn into water, eventually. You heat water, and it turns into steam, only eventually. Why

do these conversions happen? Because of heat that you give. In a solid, atoms are close together, they

are tightly packed. Thus the random movement is not there. There is only small vibration of atoms

about their positions. When you heat a solid, these vibrations increase. As you continue heating the

solid, these vibrations grow so stronger that they overcome the force that was supposed to hold the

solid. The solid breaks and turns into liquid. In liquids, there is some movement. Unlike solids,

liquids can flow. When you heat a liquid, you provide energy to its constituents and eventually, they

become free. Liquid turns into gas. Gas is that state of matter in which constituents are no longer

bounded, they are ultimately free from all bounds and move around randomly. Heat is responsible for

the changes that you see in your immediate environment. Consider evaporation. You may have studies

about evaporation when you were younger. Do you still remember it? It involves heating. In fact,

evaporation speeds up upon heating. The surface molecules get heated first, thus they are the ones

which turn into gases. Evaporation is a surface phenomenon. It is a continuous process. The question

that comes ahead is: “If rivers and oceans are always being evaporated, will they get empty some

day?” The answer is not obvious as you may think.

You think you know it. You say that evaporation and raining are two simultaneous processes. You say

that if sea water gets evaporated, it will return as rain someday. You seem to be correct. Nature loves

harmony. But have you heard of stories that rivers dry too? Suppose we have river ‘A’ in city ‘C’.

But this city is a strange city. Evaporation occurs but it is one of the driest regions in the country (this

is obviously possible too!) The river evaporates completely in 100 years (just to give you an idea)

and it rains only once in 10 years (a very dry city) – what do you think will happen? Do you see what

I am trying to point out? The river will someday vanish. Did the same thing occur on the planet Mars?

Try to think about it!

What are the uses of heat? What keeps you warm? Heat! Mars is too cold to sustain life. Mercury is

too hot. One needs a perfect location. It just so happens that our planet earth is set in the perfect spot.

Heat energy is very necessary and I do not need to tell you the examples. In the next chapter, we will

learn about energy. What is energy? Let us understand...

Chapter 4

Understanding Energy

I am very energetic. Are you too? What is energy? Why do we use this term in our daily lives?

Actually, physics involves a different meaning of the word energy. But one can use this word without

any fear in his or her life. You eat food, you get energy. Why do you get energy and where do you get

it from? It just so happens that plants, roots and trees in our surrounding are capable of gathering

sunlight and they convert it into food energy. This fact is known to every person in the world. Plants

make food. Then you eat food, you get energy. You get energy to do work.

What is work? A man holds two baskets filled with water for two hours. He is standing under the sun.

He is covered all in sticky sweat. Yet he did no work if physics is considered – in real life, he was

given a punishment. In physics, work and energy are very different terms from what we know in real

life. Here we are going to talk about energy but in this way only, you will get an idea of what work

really is.

Imagine a car travelling at 40 mph. You may have heard about kinetic energy which is energy

possessed by an object due to its linear motion. What is it and how do we know that this car has

kinetic energy? We know this because this car has ability to do work. If this car collided with a

bicycle, energy will be transferred. We discussed in the first chapter that when a body collides with

another body, momentum is transferred as per the given conditions. Then, the bicycle will fall at some

distance after the impact. The car would come to a halt. The energy due to its speed has vanished.

This energy has to go somewhere, it cannot vanish like that because nature loves harmony. What

happened? Actually, the bicycle gained the energy. The car slowed down, say to 15 mph, but it still

has kinetic energy equivalent to 15 mph, the remaining energy had been transferred to the bicycle (the

bicycle moved too!) and also to the heat and sound energy during the accident.

This is a fundamental result. Energy cannot be created or destroyed. Energy can only be converted

from one form to another. Sun does not create light energy arbitrarily. How does sun make light? Do

you think it creates energy? No, never, never, never. Sun, in fact all the bodies in the universe are

only capable of converting one form of energy into another form. Before understanding these

conversions, we must know something about these forms.

The first form of energy that we talked about was heat energy, in the previous chapter. In this chapter,

we began with kinetic energy, i.e. energy due to motion. The next type of energy is potential energy.

Potential means ability or capability. To understand potential energy, we must understand about

references. Imagine that you are living on a three floored building. This does not include the ground

floor. Thus, this building actually has four floors. The ground floor is used as a reference. One can

say that ground floor is the lowest level or the zero level. Then, as you go up, the levels increase.

With respect to the zero level, the top level is called the third level. So you go like this: 0, 1, 2, 3 and

you are at the top. If three objects are on the ground floor, i.e. they are on the zero level, they have

zero potential energy. If these objects are on the first level, their potential energy is no longer zero.

One of the objects is a leather ball. This ball can fall off from this floor and hurt somebody on the

zero level (on the ground floor) but what would be the consequence if this leather ball were to fall

from the third level to the zero level? This could lead to more severe injury. The ball has gained

further potential energy. One can say that potential energy is energy due to height. But potential energy

is relative, one has to first choose the zero level. This zero level serves as the reference. This level

has zero potential energy and thus, we call it zero level.

The next type of energy is sound energy. How does sound energy do work? Sound is a wave and a

wave is equivalent to energy. A wave carries energy. Sound energy can shatter tall buildings. It

requires energy to make sound. How do we make sound? We make sound by speaking. But media are

required to convey sound energy. Sound cannot travel without a medium. When a bomb explodes,

much of its energy is converted into sound energy. This is one of the many examples of why sound is a

form of energy.

Light is also a form of energy.

Then there is electrical energy.

You will be amazed to know that mass is another form of energy. If you have read about Einstein’s

energy-mass equivalence, mass is a compact form of energy. This leads us to atomic bombs, really

devastating for the society. Now that we know about different forms of energy, we can learn about

conversions. We will learn mutually. You teach me and I teach you.

The first example that I want to give you is hydroelectric power. Water falls from height (having

potential energy) which is used to gain electrical energy. The potential energy of water is used to run

turbines and current electricity is produced and stored. In this case, potential energy is converted into

electrical energy.

The second example is of an electric bulb. When current runs (electrical energy) it heats the tungsten

wire inside the bulb (heat energy) and eventually, the heat is enough to get light (light energy) In this

case, there are two conversions. Electrical energy is first converted into heat. Heat is then converted

into light energy.

The next example that I want to give you is about a falling body. Imagine that a body is at the edge of

a cliff. The cliff is 100 meters high. Thus, this body has initially got some potential energy with

respect to the ground (here is our zero level!) now let this body fall. As it falls, gravitational

acceleration will increase the speed of the body. Thus some of the potential energy is converted into

kinetic energy – energy of motion. In the end, when the body hits the ground, it hit it with some

velocity – having kinetic energy but it will have zero potential energy on the ground.

The last and the most bizarre example of conversion I want you to know is about how sun makes light.

Sun actually uses its mass to make sunlight. It is converting its mass (energy source) into light

(conversion) – eventually after millions of years, there will come a time when sun will use all of its

mass and would meet its end. Imagine how massive sun should be to light for another million years!

We have seen multiple examples of how energy is converted from one form to another. These

different forms of energies exist between us but we hardly give any importance to them – we hardly

appreciate their existence. Now that you know a lot about energy, it is time for revision 2.

Revision 2

1. What is heat and what is temperature? Are the two same? Explain your answer.

2. Try to touch a hot cup of tea with a metal rod. You hold the rod and let one of the ends touch

the cup. After some time, what do you feel?

3. Take another hot cup of tea, this time touch this cup with a plastic stick. What do you feel

this time? Compare this with what you felt in activity (2)

4. List all the forms of energy that you see in your surroundings.

5. What is conservation of energy?

6. List any two examples of conversion of energy.

7. How can you use sunlight to make electrical energy? What is this process called? Are you

destroying any energy?

8. What is energy?

9. If you are on the top floor of a 100 m tall building and your brother (you and your brother

have the same mass – just for the sake of simplicity) is on a floor such that his potential

energy is exactly half of that of yours. This building is 10 floors high. Where is your

brother?

10. How do stars make light?

11. Why should energy be conserved?

Chapter 5

Understanding Light

Without light, you cannot see. Try to find your way in dark, if you are familiar with the things around,

you will do this with ease. But try to walk around in a dark and gloomy tunnel where there are

numerous items scattered on the floor. You would hurt yourself. Darkness can be removed with lights

of all colours. Most people are not aware of the fact that colours are also lights. In fact, light that we

see is made of seven different colours and the image below tells you what I want to convey.

Just like our ancestors wanted to understand motion and gravity, they were also keen about the nature

of light. They asked numerous curious questions: What is light? What is it made of? How fast does it

travel? Where does it come from? What is its nature? Only a curious and inquisitive mind can ask

such questions. Take for example Carl Sagan, who was once puzzled by the stars. He asked, what

were they? The most usual answer that he got was ‘ They are lights in the sky, kid.’ The correct and

somewhat more satisfying answer that he found was that stars were distant suns. This allowed him to

wonder at the grand design of the universe and left his young impressionable mind in joy.

So when kids ask questions, they are trying to know of something – in fact they may be curious to

learn something new. We, as adults should promote their desire and not suppress it with usual and

boring answers. With kids, adults often become smarter. So what will you tell your kid if he asks you

‘ How does a bulb glow?’ You tell him (or her) about conversion of energy. What is he asks you about

light? So let us understand what light actually is:

It was Isaac Newton (yes, again!) who first questioned about the nature of light – he compared light as

a stream of particles. He believed in his particulate model of light. Just as a pen or pencil or any

other object is made of small particles called atoms – Newton assumed that light, too, was composed

of small microscopic particles that carried light energy.

In this way, Newton could explain reflection – the way you see yourself on the mirror. You see your

reflection because light particles move and collide with shiny surface of mirror and bounce back.

Compare these particles with bouncing balls. You aim a ball at a wall and it bounces back at you.

Light is thought of as small balls bouncing back at you. But Newton explained that the reflection is not

always perfect. For example, you can also see your reflection on the back side of a spoon but it is not

as clear as what you see on the mirror. This is because rough surfaces as explained by Newton would

always absorb most of the light particles. Those surfaces that do not absorb but always allow the light

particles to bounce back produce the best reflection – like that mirror next to you.

But Newtonian view of light was challenged. Newton could not explain refraction. He did but his

explanation was vague. Refraction is very different from reflection. While reflection is bouncing back

of light rays, refraction involves bending of light rays. You may have experienced refraction when

you are in a swimming pool. You appear to be shortened. The picture below clearly illustrates what

refraction is – it is the bending of light when light changes media (such as from air to water) and

Newtonian theory of gravity was not fit to explain bending.

A new idea was waiting for approval – that light was a wave that carried light energy. This idea was

put forward by Christian Huygens who stated that light travelled as a wave. He stated that wave

travels with some speed and when light enters from one medium to another, its speed changes, thus

bending occurs. But again, Huygens theory could not perfectly explain reflection. Actually the idea is:

Both theories could explain some aspects of light but both theories also failed at certain light

phenomena. Scientists were confused about what was correct and what was wrong. The major

belief was that light couldn’t be both!

Newton’s theory said that if you shine a torch at a wall and shine another at the same wall, you make

a brighter light on the wall – the wall lights up! But there was a contradictory phenomenon that

scientists discovered, including Thomas Young. He found that when a light ray from a similar source

passed through two very narrow slits – as thin as a thread, there were patterns of bright and dark

patches. He expected only brightness – as he believed in Newton but what he saw amazed his eyes!

He found that light plus light could also create darkness! So in our analogy, it is like you shine the two

torches at the wall, and you see no brightness, nothing but darkness! The diagram below shows you

the pattern as seen in the two-slit experiment.

Scientists all around the world started to discard particle theory because it did not predict such a

thing! They started analyzing the wave model of light and found a possible explanation. Below you

see a wave, it has ups and downs as you see in a water wave.

If you mix two waves you can create two patterns: One of them is called constructive mixing and the

other is termed destructive mixing. If you look at a wave, you can create these two patterns. When

two waves mix at the same level, they produce light – light + light = much brighter light but when you

mix two waves differently – at different levels, you create a dark patch – light + light = darkness. Just

look at the diagram below to understand this again.

It is like addition. You add 2 and 2, only to get 4. But if you add 2 with (-2) you get nothing. This is

what happens with light waves. Same levels mean same signed waves and different levels mean

waves of opposite phases. This is pure analogy.

But the story is not finished. Particle model wanted revenge, wave theory had overthrown its power

when Young did double-slit experiment but when Hertz performed photoelectric experiment, only

particle model of light could explain what was happening.

Heinrich Rudolf Hertz, a German experimental physicist found that when light rays of suitable

(required) energy hit a metal surface, electrons were emitted out of the metal – like a current, when

light (photo) hit metal producing current – thus the name photoelectric, relating light and electrons.

Hertz also found that when a negative charged metal plate was placed under incident light of required

energy, the negative charge on the metal decreased. Also, when a positive plate was kept, it got more

and more positive. This led Joseph Thomson, an English physicist, to assume that metal atoms, in fact

all atoms, had tiny particles that carried negative charges. He explained that when light of suitable

energy fell on metal like sodium or calcium, electrons (which was the name of these negative

particles) were emitted out with some kinetic energy.

So what was happening? Light energy was changing to kinetic energy of electrons. At first, it seemed

that wave theory would easily be able to explain this phenomenon, and that particle model would not

be needed. But as it turned out, wave theory failed. We would not further discuss of what happened –

but one thing was clear. Light was of mysterious character – it behaved like wave at times (light +

light = darkness) and like particle at times, to explain emission of electrons from metal (in which light

particle transferred their momenta to electrons to give these negative charges some kinetic energy). If

you want to know more about photoelectric effect and about its explanation, you should check out this

book: Light, colours and the physics behind or Let us discover modern physics in which you learn

about wave-particle duality.

Now let us understand something about what colours are. You see a variety of colours around you.

You see red, green, yellow, blue and so many colours, that it is almost impossible to list them all. But

what are they?

Actually a colour is a light of special nature. To each colour, a special property is associated – this is

called frequency. Violet or blue is the most frequent light. Red and orange are less frequent light

waves. It is best to understand colours as waves. So when you see red colour, you are actually

looking at a particular frequency of light, a slight increment or decrement from the red frequency lets

you create a new colour. This is used by computers that can create millions of colours by varying

frequency of standard colours. The sunlight that you see is composed of seven different colours. They

mix so well that sunlight appears to be white. You can see this for yourself, take a CD, and let

sunlight fall on it. Do you see different colours? These arise from the sunlight as sunlight is composed

of them. Why do we see colours? This question is well answered in the next chapter, called

Understanding Atoms.

Chapter 7

Understanding Atoms

All matter that we see is made of tiny particles called atoms. A long time ago, Democritus thought of

an entity that was indivisible, he called it the final stage of all matter. He imagined that what would

he get if he keeps on cutting an item with a very sharp knife? Will there be an ending stage? He stated

that yes there is an end and he named this an atom.

So, according to Democritus, all things were made of tiny indivisible particles called atoms.

According to him, one could not further divide atoms into smaller particles. That would be

impossible according to him. John Dalton was an English school teacher whose theory of atoms was

the first to leave an impact on the scientific community. He stated that different atoms represented

different elements. He stated that atoms could neither be created, destroyed nor be transformed into

other atoms. In a chemical reaction, according to him, there is only a rearrangement of atoms.

Dalton’s theory assumed atoms to be indivisible and spherical, which we now reject.

Joseph Thomson, discovered electron, a sub-atomic particle contradicting Democritus and Dalton.

His experiment was a consequence of photoelectric effect. He found that all things were made of

atoms, but in turn, all atoms had a negative charged particle which he named electron. Not only that,

Thomson also predicted the existence of a positive particle – since atoms are neutral as a whole.

Proton, a positive particle was soon discovered. Proton has charge exactly equal to that on an

electron but the polarity is opposite. An electron is negative, on the other hand, a proton is positive.

Two sub-atomic particles were discovered and the name atom, which meant indivisible in Greek was

contradicting the then theory.

Later experiments showed the possible existence of a third sub-atomic particle. Obviously this

particle had to be electrically neutral otherwise it would make an atom charged up (an atom is neutral

by birth)

Rutherford found that masses of atoms found experimentally were not agreeing with those calculated

on paper. On paper, we were considering the masses of protons and electrons, yet we were very short

of the masses found in spectrometer experiments.

Rutherford modified Thomson’s theory by stating that there was another particle inside an atom. To

illustrate this, he had designed an experiment. Locations of protons and electrons were not stated

clearly in Thomson’s model of atom. Rutherford had planned to bombard high-speed alpha particles

( by the way, alpha particle is a charged particle which has charge exactly double of that on a

proton) on a very thin gold-foil. He was actually measuring interaction of alpha particle and gold

atom. He found amazing stuff! The results were so astonishing that he had to totally change the

Thomson’s model!

Thomson had created a model like that of a sphere – so he assumed atoms to be spheres, and he also

assumed that all the mass of atom was uniformly distributed in this sphere – but Rutherford disproved

his model.

Rutherford found that most of the alpha particles passed straight through the foil. This meant that most

of the atom was empty space. If it were uniformly distributed with mass, the alpha should have

rebounded, like a light particle hitting a mirror.

Another thing that Rutherford found was that a few particles deflected from their usual path at small

angles, say 15 degrees or so. This meant, that somewhere inside the atom, a few locations were

occupied by electrons, which were applying an electric force on alpha particles, causing them to

deflect.

He found that one in 20000 alpha particles rebounded exactly at 180 degree angle. He assumed that

the particle must have had hit a very dense solid. This was named nucleus. Rutherford stated in his

atomic theory that most of the mass was located at extremely small and extremely dense area called

the nucleus, located at the centre of the nucleus and that electrons were revolving around the centre

just as planets revolve around the sun. Nucleus contained protons and neutrons, (the neutral particles)

and electrons revolved around the nucleus.

There is one way so that you can experience Rutherford’s experiment. This experiment is discussed in

the revision and I hope that you do this one, it is really interesting.

Now we will try to know how colours are made. The theory of atoms is not yet over. There is a lot of

understanding that is left, you would be amazed but Rutherford’s model was falsified by Neils Bohr,

whose model was again falsified by the collective efforts of Heisenberg and Schrodinger. You see

science and especially physics is about checking and validating. No matter who you are, if one single

experiment disagrees with your theory, your theory is falsified and no longer valid. For the sake of

simplicity, we will discuss about colours in the simplest way possible, for a detailed and simplified

explanation, you should also invest your time on one of these books:

1. Light, colours and the physics behind, this book is devoted to the physics of colours

2. Let us discover modern physics, if you want to know more about atomic theory by Bohr and

Heisenberg’s modification in the simplest language possible

3. What is this world made of? A book which discusses atomic theories for the best of your

understanding of this world and beyond

The main objective of all books is to enjoy physics, because physics is beyond equations, it is in

experience.

So we were talking about colours. Colours are actually made by atoms. So imagine a yellow

coloured wall. Why is it yellow? It is yellow because light falls on its surface and it reflects back

only the frequency corresponding to yellow. When it is very dark in the room you are in, you do not

see the wall. So you see the wall, when light falls upon it. According to Einstein, light is made of

particles which he named photons, so when these photons fell on the wall, having some energy, they

excite atoms of the wall. A neutral and not so excited atom has no absorbed energy. As we already

know, when light falls on a rough surface, most of the incident energy is absorbed and only a

particular frequency is reflected back, which we see as its colour. When light falls on a very smooth

and very shiny surface, such as a mirror, almost all (sometimes 100%) the light is reflected back, thus

you see your reflection, mirror does not have a colour because all the light that falls on it (which is

white light of sun) is reflected back (which is again a white light)

So what we see as colours are actually frequencies, visible frequencies. So when light falls on the

atoms of wall, these atoms get excited, an excited atom is the one which has absorbed energy. But

atoms are not stable at all in their excited states. They want to get normal. How can nature make them

normal? It is done by re-emission of the energy that they had absorbed. This re-emission is what we

see as colour. In the dark, no light falls on the atoms of this wall, no excitation occurs and thus no

colours are seen.

Maybe this seems confusing. But if you read the above two paragraphs again and very carefully, you

will understand what I mean, but I strongly recommend Modern Physics o r Light, colours and the

physics behind. Your understanding about atoms and light would be much stronger than it is now!

Revision 3

1. What is light? How do stars make light?

2. How do you see your reflection on a mirror? How did Isaac Newton explain reflection?

3. What is refraction? Have you ever experienced refraction? Discuss about it.

4. What is sunlight made of? Take a chart paper and cut a circle. Colour the seven colours of

the sunlight on this circle and stick this paper circle on a solid cardboard. Now you have

made a circular disk. The colours are violet, indigo, blue, green, yellow, orange and red.

Rotate this disk fast enough. What do you see? Why?

5. What was the argument between Newton and Huygens?

6. How did the double slit experiment falsify the particle theory of light and establish the wave

model?

7. So what exactly is light? Is it a wave or a particle?

8. What is an atom? Is it indivisible as Democritus had assumed?

9. State the postulates of Dalton’s atomic theory. Why do you think John Dalton is considered

as the father of modern atomic theory?

10. What is photoelectric effect? How did Thomson use this to predict the existence of a sub-

atomic particle? Explain in detail.

11. Why did Rutherford suspect Thomson’s model of atom? What experiment did he suggest?

12. What were the results of Rutherford’s experiment with alpha particles? How did he

completely change Thomson’s model of atom?

13. What is a nucleus?

14. Why should the number of protons and the number of electrons be the same in a neutral

atom?

15. An atom has 10 protons and 13 electrons. Is it neutral? Express its charge equivalent to that

on an electron.

16. What is an excited atom? Is an excited atom equally stable as a neutral atom?

17. Rutherford’s experiment can be replicated at home! Stand next to a wall. Draw a very small

target on this wall, a target as big as a tennis ball. Now stand 50 metres away from this wall

and aim tennis balls at it. Do you hit the target? Most of the time, you will fail – this same

thing happened with Rutherford. 1 in 50 times, you may hit the target! Rutherford is proud of

you…

18. How are colours produced? Why do you see green colour of grass during the day and not

see it at all when it is totally dark?

Chapter 8

Understanding the Universe

We understood about motion and gravity. We discussed about the nature of light, which is a form of

energy. We now know what heat is and what atoms actually are. All these things and all these

quantities are a small part of the grand design of the universe. In this chapter, we get our attention

toward the universe. First of all, we learn about the solar system.

Our solar system had 9 planets, but now, due to our definition of what a planet is, we have discarded

Pluto as a planet and now call it a dwarf planet. Solar system is incomplete without sun, sun’s gravity

holds this system together. All the planets, their moons, dwarf planets, comets, asteroids revolve

around the sun.

Solar system is a system and it is moving as a system in the universe. Sun is not static, it is also

revolving around the Milky Way galaxy’s centre. This system is a very small part of the galaxy.

Aristotle had thought that sun, and all the other bodies moved around earth, but Galileo, Copernicus,

Kepler, Newton and later scientists and observations firmly established that sun was the centre of the

solar system. I am not going to discuss stupid facts like the diameter of the sun, or mass of the planets.

These are not necessary, the truth is that sun is the most massive body in the solar system, thus, all

bodies revolve around it. Jupiter is the second most massive body in the solar system. It is the largest

planet in the solar system, and I hope you agree with me, that earth and Saturn are the two most

beautiful planets in the solar system – earth because it sustains life and Saturn because of its beautiful

rings.

Now we turn our attention on galaxies. Back in the 19th century, astronomers had discovered many

nebulae in the universe. They thought that they were all parts of Milky Way. But Edwin Hubble

measured distances to those so-called nebulae and they turned out to be distant galaxies! Hubble

established the fact that the universe was full of galaxies. A galaxy is a group consisting of stars.

Maybe Milky Way contains billions of stars. We do not know the exact number but we try to digest

the fact that galaxies are so large that they must be home to at least a million stars, or maybe even

more. Universe is very big. It is way beyond our imagination. It is home to millions of galaxies, we

do know this. But what after that?

Motion is very much prevalent in the universe. We are moving, all the planets are moving and the sun

is moving around the galaxy. It was assumed a century ago that the entire universe was static. It is

hard to imagine an object to be at rest. It is always moving with respect to something. For example, a

book kept on a table is at rest with respect to you, but it is in motion when Neil Armstrong sees it

from the moon! All the planets are moving too, the sun is itself in motion. In fact, the entire universe is

in motion – nothing is stationary. To know about this motion in detail, switch to the book Let us

discover Physics: Appreciating Nature.

One thing that we know about the universe is that it is also in motion. It is expanding. To know about

this expansion, you must know about Doppler Effect, which is explained very much in detail in the

book ‘ Let us discover Physics.’ But here we would like to know what causes this expansion? We ask

ourselves: Will this expansion ever stop?

We think of two forces. One of the force is gravity, the force that we think could stop the expansion of

the universe. The other force which we think could accelerate the expansion is unknown. This is

opposing the action of gravity. If there is enough matter (enough mass) in the universe, gravity would

ultimately cause the universe to stop expanding and shrink back to smaller sizes. On the other hand,

the mystery force or dark force would cause the universe to expand forever. Both would ultimately

lead to death of the universe.

How did the universe begin? Why do we study about the universe in a book about physics? What do

we gain from it? Actually the universe is governed by four fundamental forces. These four are gravity,

electromagnetism, weak and strong nuclear forces. To know more about these forces, you must read

Let us discover Physics. But what are we trying to say? I am saying that if we keep on studying the

universe, someday we may discover another fundamental force, which will change the way we look

at the universe. Anything can happen and thus physics can change very rapidly. How did the universe

begin? No one knows for sure. But one theory called the big bang theory possibly answers the

questions of creation, not of creation, in fact about the beginning. The universe is currently expanding,

we do not know what may happen at the next moment, but if we run the cosmic movie backward, we

see that the galaxies get closer together. We ultimately get to a time when all the galaxies were

exactly at the same location.

Maybe we are getting out of the scope of this book, but we do know one thing: Physics and universe

get related in astrophysics. It is an adventurous journey of the entire human race.

Chapter 9

Understanding Physics

Physics is an awesome journey of understanding nature. Some people try to find physics in equations.

I say that physics is beyond equations, it is in experience. Some people boast of solving complex

numerical problems, without actually realising the physics working behind the scenes. What is

important to understand physics?

1. Qualitative analysis

2. Quantitative analysis

3. Analogy

4. Relationship

5. Love and joy of physics

Qualitative analysis is extremely important. This allows you to relate things that you see. For

example, volume and pressure are two separate physical quantities. A balloon has gas particles

which move randomly, colliding with the walls of balloon, thus applying pressure. For the sake of

simplicity, assume that a balloon has 6 particles. These 6 particles apply pressure on the walls of

balloon. This balloon has volume V, which provides the space for movement. Now you decrease the

volume to V/2 – what have you done? You have put a limit to the volume in which the particles can

move around, thus increasing the collisions with the balloon wall. You have actually increased

pressure.

On the other hand, you can use quantitative analysis, i.e. using numbers and calculations. You could

measure and experiment. Qualitative analysis is necessary to make ideas, quantitative analysis is

required only to test the ideas. Thus, in my opinion, qualitative analysis is vital. I can’t explain this

but I am in love with physics – I enjoy doing problems and I also enjoy nature. Love and joy are both

required while understanding physics. It is the love of physics and the joy of knowing new stuff that

keeps the human race driven. Analogy and relationship are necessary parts of understanding physics.

Physics is fun and if you know the rules, you can enjoy it too! So let us discover physics!

Other books that you might be interested in:

About the Author

If you are a curious kid, Vedang Sati is just like you. He was born on January 4, 1996 and his interest

in astronomy came forward when his mother gifted him a book on space entitled 'Deep Deep Space.'

Since then, he has taken the subject very seriously. He questions about vivid natural phenomena

because he believes that questioning is important as it opens the pathway for a curious mind. Growing

up in New Delhi, India, watching Cosmos and listening to Stephen Hawking's electronic voice - that

all has inspired him to indulge in this amazing cosmic adventure. He loves to draw in his spare time.

Someday he hopes, he will solve the most confusing riddles of the universe. With this goal in mind

and to inspire every single individual toward science, here he is, on his spaceship, out on an amazing

cosmic adventure! Visit him at www.facebook.com/questioninggod which is another home to physics

lovers! Please leave a review for this book at www.amazon.com !

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Table of Contents

Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 7

Chapter 8

Chapter 9