Class 9 Science Chapter 1 Notes

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Class 9 Science Chapter 1 Notes

Chapter Name: - Matter In Our Surroundings

Class 9 Science Chapter 1 Notes_

Section - A
(Questions - Page 3 )

1. Which of the following are matters?
Chair, air, love, smell, hate, almonds, thought, old, lemon, water, smell of perfume.

Every physical thing in this universe that occupies space and has mass, is called mater. On the basis of this definition, the following things are considered matter: 

Matter:- Chair, air, almonds, cold drink, smell of perfume.

(The remaining things like love, smell, hate, thought, and cold are not physical things as they do not possess any space and have no mass. They convey emotions, ideas, or thought but they are symbolic in nature. Therefore, they all are not considered as matter.)

2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.

The smell of hot sizzling food reaches us several metres away because the particles of hot food diffuse into the air at a higher rate than the particles of cold food.

Reason:- Particles of matter are continuously moving as they possess kinetic energy. With the increase in the temperature the kinetic energy of the particles also increases. On heating, diffusion (intermix of particles of two different types of matter) becomes faster.

3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

The matter is made up of particles. These particles of matter attract each other. A diver is able to cut through water in a swimming pool because the force of attraction between the particles of the water is weak.

4. What are the characteristics of the particles of matter?

The following are the characteristics of the particles of matter: –

1. Particles of matter have space between them

2. Particles of matter are continuously moving

3. Particles of matter attract each other

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Class 9 Science Chapter 1 Notes

Section - B
(Questions - Page 6)

1. The mass per unit volume of a substance is called density (density = mass/volume). Arrange the following in order of increasing density - air, exhaust from chimneys. honey, water, chalk, cotton, and iron.

The order of increasing density of the given substances.

exhaust from chimney < air < cotton < water < honey < chalk < iron

(The exhaust coming out of the chimney usually rises up. It indicates that its density is lesser than that of air. The hotness present in it makes it lighter.)

2. a) Tabulate the differences in the characteristics of states of matter.

The difference in the characteristics of three states of matter in tabular form is as follows.

SolidLiquidGaseous
Definite shape, distinct boundaries, and fixed volumesNo fixed shape but have a fixed volumeNeither have definite shape nor the definite volume
Particles have a little or no space in betweenParticles have greater space between them as compared to solidsParticles have greater space between them as compared to liquids
Maintain their shape when subjected to an outside forceDo not maintain their shape. They flow and take the shape of the containerDo not maintain their shapes. The particles move randomly in all directions.
Can diffuse into liquids but the rate of diffusion is the least among all threeThe rate of diffusion is greater than the solids.The rate of diffusion is greater than the liquids
Incompressible or very hard to compressCompressible to some extentHighly compressible

2. b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.

Rigidity: – A tendency of the substances to maintain their shape when subjected to an outside force.

Compressibility: – A tendency of the substances to be reduced to fit into the lower volume.

Fluidity: – An ability of the substances to flow. eg. liquids and gases.

Filling a gas container: – Even a small volume of gas takes up the whole space inside a gas container. Also, a gas can be highly compressed and filled into a container.

Shape: – The noticeable appearance of a substance. 

Kinetic energy: – The energy possessed by an object by virtue of its speed.

Density: – Mass per unit volume of a substance is called density.

3. Give reasons:
a) A gas fills completely the vessel in which it is kept.

The force of attraction between the molecules of a gas is very weak. They move randomly at high speed in all the directions. This is the reason why a gas fills completely the vessel in which it is kept.

b) A gas exerts pressure on the walls of the container.

The particles of a gas move about randomly at high speed in all the directions. This random movement causes the particles to hit each other and also the walls of the container. The force produced by the continuous movement of the particles exerts pressure on the walls of the container.

c) A wooden table should be called a solid.

The wooden table carries all the characteristics of solid substances. It has definite shape, distinct boundaries, and fixed volume. It is rigid and maintains its shape subjected to an outside force. Hence, a wooden table should be called a solid.

(d) We can easily move our hand in air, but to do the same through a solid block of wood, we need a karate expert.

The force of attraction between the particles of a gas is very less. So they have a large space between then allowing our hands to move through it.

Whereas, the force of attraction between the particles of wood is very large. Due to this force of attraction, they are closely packed and have not enough space to move our hands through them. A karate expert can move his hand through a block of wood by overcoming this force. 

4. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Liquids generally have lower density as compared to solids but water has some exceptional qualities. The density of water is maximum at 4ºC and its freezing point is 0ºC. 

So the liquid form of water has a larger density than its solid form, as water is liquid at 4ºC and solid at 0ºC. A substance having lesser density than water will float on it. Hence the ice float on water.

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Class 9 Science Chapter 1 Notes

Section - C
(Questions - Page 9)

1. Convert the following temperature to Celsius scale:
a) 300K
b) 573 K

a) Given temperature = 300K

As Value in Celsius = Value in Kelvin – 273

we get,

Value in Celsius = 300 – 273 => 27

So, 300k = 27ºC

 

b) Given temperature = 573K

As Value in Celsius = Value in Kelvin – 273

we get,

Value in Celsius = 573 – 273 => 300

So, 573K = 300ºC

2. What is the physical state of water at:
a) 250°C
b) 100°C

The physical state of water

At 250ºC = Gaseous state

At 100ºC = Liquid as well as gaseous state

3. For any substance, why does the temperature remain constant during the change of state?

During the change of state, the heat energy supplied to a substance is used up to overcome the force of attraction between its particles. This heat does not increase the temperature of the substance so it is known as latent heat. That is the reason why the temperature remain constant during the change of state.

4. Suggest a method to liquefy atmospheric gases.

The pressure and temperature determine the state of a substance, whether it will be solid, liquid, or gas. Therefore applying pressure and reducing temperature can liquefy gases.

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Class 9 Science Chapter 1 Notes

Section - D
(Questions - Page 10)

1. Why does a desert cooler cool better on a hot dry day?

The rate of evaporation depends upon an increase in temperature and the amount of water vapour present in the air. On a hot day, the rate of evaporation of water inside a desert cooler increases due to an increase in temperature. The large latent heat of vaporisation of water helps to cool the surroundings. 

2. How does water kept in an earthen pot (matka) become cool during summers?

The tiny pores present in the earthen pot act as a passage for the water present inside of it to reach out to the outer surface. The evaporation is a surface phenomenon and increases with the increase in the surface area. The water from the surface of the earthen pot starts evaporating at a higher rate making the water cool inside the pot.

3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?

The intermolecular force of attraction between the particles of acetone or petrol or perfume is very less. So, it evaporates at a very high rate. When we put any of these on our palm their particles gain energy from our palm or surroundings and evaporate at a faster rate causing the palm to feel cold.

4. Why are we able to sip hot tea or milk faster from a saucer than a cup?

The surface area of milk or tea poured in a saucer is more than that of a cup. The evaporation is a surface phenomenon. The rate of evaporation increases with an increase in surface area. The hot milk or tea becomes cool faster in a saucer rather than a cup so we are able to sip them faster.

5. What type of clothes should we wear in summers?

We should wear cotton clothes in the summer.

Reason: – Cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation. During evaporation, the particles at the surface of the liquid gain energy from the surroundings and change into vapour. The heat energy equal to the latent heat of vaporisation is absorbed from the body leaving the body cool.

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Class 9 Science Chapter 1 Notes

Section - E
(Questions - Exercise)

1. Convert the following temperatures to the Celsius scale.
(a) 293 K
(b) 470 K.

a) Given temperature = 293K

As Value in Celsius = Value in Kelvin – 273

we get,

Value in Celsius = 293 – 273 => 20

So, 293K = 20ºC

 

b) Given temperature = 470K

As Value in Celsius = Value in Kelvin – 273

we get,

Value in Celsius = 470 – 273 => 197

So, 470K = 197ºC

2. Convert the following temperatures to the kelvin scale.
(a) 25°C
(b) 373°C.

a) As Value in Celsius = Value in Kelvin – 273

So we get, Value in Kelvin = Value in Celsius + 273

Given temperature = 25ºC

 

Value in Kelvin = 25 + 273

So, 25ºC = 298K

b) Given temperature = 373ºC

Value in Kelvin = 373 + 273

So, 373ºC = 646K

3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.

The naphthalene balls show the property of sublimation (change directly from solid state to gaseous state without changing into liquid). They convert into the gaseous state directly over a period of time and disappear.

(b) We can get the smell of perfume sitting several metres away.

Due to the high speed of the particles and large space between them, gases show the property of diffusing very fast into other gases. That is the reason why the particles of perfumes diffuse easily into the air and we can get the smell of these sitting several meters away.

4. Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.

The increasing order of forces of attraction between the particles of the water, sugar, and oxygen is

 oxygen < water < sugar

5. What is the physical state of water at—
(a) 25°C (b) 0°C (c) 100°C?

The physical state of water

At 25ºC → liquid

At 0ºC → solid, liquid, vapour (This is called the triple point of water)

At 100ºC → liquid, vapour

 

6. Give two reasons to justify—
(a) water at room temperature is a liquid.

The water possesses the characteristics of a liquid at room temperature. It has no fixed shape but has a fixed volume and shows fluidity at room temperature.

(b) an iron almirah is a solid at room temperature.

The almirah possesses the characteristics of a solid at room temperature. It has a fixed shape, distinct boundaries, and fixed volume.

7. Why is ice at 273 K more effective in cooling than water at the same temperature?

The particles of ice at 273K possesses more energy than the particles of water at the same temperature. 

8. What produces more severe burns, boiling water or steam?

Steam produces severe burn as the particles of steam have more energy than hot water at the same temperature. This is because the particles of steam absorb extra energy in the form of the latent heat of vaporisation.

9. Name A,B,C,D,E and F in the following diagram showing change in its state

Name A B C D E and F in the following diagram showing change in its state-question

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Class 9 Science Chapter 1 Notes

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