Class 9 Science Matter in Our Surroundings
Introduction
When we look around, we see many different things with various shapes, sizes, and textures. Everything in the universe is made of something called “matter.” Matter includes the air we breathe, the food we eat, stones, clouds, stars, plants, animals, and even tiny drops of water or grains of sand. All these things take up space and have weight, which means they have mass and volume.
Since ancient times, people have tried to understand the world around them. Early Indian thinkers believed that everything, whether living or non-living, was made of five basic elements called the “Panch Tatva” — air, earth, fire, sky, and water. Ancient Greek philosophers had a similar idea about the basic elements of matter.
Today, scientists classify matter in two ways: by its physical properties and by its chemical nature. In this chapter Matter in Our Surroundings, we will learn about matter based on its physical properties. We will explore its chemical aspects in later chapters.
Matter
All those substances which have mass and volume are called matter.
- Everything in the world is the matter.
- Matter is made up of particles and they are extremely fine.
Physical Nature of Matter
- Matter is made up of particles
- How small are these particles
Characteristics of particles of matter
- Particles of matter are much smaller.
- Particles of matter attract each other.
- There are empty spaces between the particles of matter.
- The particles of matter keep moving continuously, that is, they have kinetic energy.
States of Matter
Matter exists in three states: solid, liquid, and gas.
1. Solid State:
The substances that have a definite volume and shape are called solids, like iron, wood, stone, etc.
2. Liquid State:
The substances that have a definite volume but no definite shape are called liquids, like water, milk, oil, etc.
3. Gaseous State:
The substances that have neither a definite volume nor definite shape are called gases, such as air, carbon dioxide, oxygen, etc.
Note: Dear friend, You have to know one more important thing which is related to the state of matter. Recentaly scientist, two more states of matter have also been discovered which are as follows
4. Plasma: Plasma is the state of matter which consist of super energetic particles.
example – Sun
5. BEC (Bose-Einstein Condensate): Bose-Einstein Condensate is a super cold state of matter where atoms act like waves, behaving as one big entity.
Can Matter Change its States?
Matter can change its state by the following.
- By changing the temperature.
- By changing the pressure.
Change of State of Matter
The process of changing matter from one state to another due to temperature or pressure is called the change of state of matter.
Effect of Change of Temperature
Melting Point
The temperature at which a solid turns into a liquid at 1 atmospheric pressure is called the melting point of the solid. There is no increase in temperature at the melting point, but the heat given is used to convert the solid into liquid. This heat is called the latent heat of fusion.
Freezing Point
The process opposite to melting is called freezing, and the specific temperature at which this process occurs is called the freezing point.
Boiling and Boiling Point
The specific temperature at which the vapour pressure of the liquid becomes equal to the atmospheric pressure is called the boiling point of the liquid, and the process of evaporation at this temperature is called boiling.
Condensation
The conversion of gas into liquid is called condensation.
Sublimation
The conversion of a solid substance directly into vapour when heated is called.
Deposition
The process of conversion of gas directly into a solid is called deposition.
Temperature
Temperature is the degree of hotness of a body.
- S.I. Unit of temperature is Kelvin.
- Normal Unit of temperature – Celsius, Fahrenheit.
Relation between Celsius and Fahrenheit
\frac{C}{5}=\frac{F−32}{9}
Evaporation
The process of changing a liquid into vapour at a temperature lower than its boiling point is called evaporation.
The process of evaporation depends on the following factors.
1. Nature Of Liquid
Substances with lower boiling points evaporate more quickly because their particles require less heat energy to break free from the liquid state and become gas.
2. The surface area of the liquid
Because increased surface area allows more liquid particles to escape into the air, speeding up evaporation due to greater exposure to air.
3. Temperature of the liquid
Because evaporation is directly proportional to temperature, evaporation rises as temperature increases, as higher temperatures provide more energy for liquid particles to escape into the air.
4. Surface area of liquid
Because surface area is directly proportional to evaporation, when there is more space for liquid to touch the air, it evaporates faster. So, bigger surfaces mean quicker evaporation.
5. Wind Speed
Because wind speed is directly proportional to evaporation and faster wind makes water evaporate faster, as it carries away water vapour molecules, speeding up the process.
6. Humidity
If the humidity is high then the evaporation is slow and if the humidity is low then the evaporation is fast.
What is humidity?
Answer: The amount of moisture or water vapor present in the air
Evaporation always causes cooling
Evaporation causes cooling because when a liquid evaporates, its particles need energy to change into a gas. This energy is taken from the liquid’s surroundings in the form of heat. As a result, the surroundings lose heat and become cooler. This is why sweating cools our bodies.
| Quantity | Unit | Symbol |
|---|---|---|
| Temperature | kelvin | K |
| Length | metre | m |
| Mass | kilogram | kg |
| Weight | newton | N |
| Volume | cubic metre | m³ |
| Density | kilogram per cubic metre | kg/m³ |
| Pressure | pascal | Pa |
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