Science Class IX

Matter in our surroundings

Can you say what is surrounding?

Everything around us is surrounding.

If we look around us, we can see different things. So, tell me what you can see in your surroundings: a table, chair, fan, door, and books. These all are matters. Also, all these have some mass and volume. They occupy some space.

Anything which occupies space and has mass is called matter. Matters have both mass and volume. Example- table, chair, water, air, etc

Physical nature of matter

Matter is made up of particles. These particles are extremely small and can not be seen by our naked eyes. They are small beyond our imagination.

Characteristics of 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.

• Particles of matter possess kinetic energy. As the temperature rises, particles move faster. The kinetic energy of particles increases with the increase in temperature.
• The intermixing of particles of two different types of matter on their own is called diffusion. On heating, diffusion becomes faster.
• The particles of matter have a force acting between them. This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another.

States of Matter

Matter around us exists in three different states, which are

1. solid
2. liquid 
3. gas

These states of matter arise due to the variation in the characteristics of the particles of matter.

The solid state

1. Solids have a definite shape and fixed volume.
2. Solids have negligible compressibility.
3. Solids have a tendency to maintain their shape when subjected to outside forces.
4. Solids may break under force, but it is difficult to change their shape. They are rigid.

Case of Rubber band, Sugar and salt, and sponge

Rubber bands, sugar, salt, and sponges are solids. A rubber band changes shape under force and regains the same shape when the force is removed. If excessive force is applied, it breaks. The shape of each sugar or salt crystal remains fixed, whether we take it in our hand or put it on a plate or jar. A sponge has minute holes in which air is trapped; when we press it, the air is expelled, and we are able to compress it.

The liquid state

1. Liquids have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept. 
2. Liquids flow and change shape. 
3. They are not rigid, and they can be called fluid. 
4. Solids, Liquids and gases can diffuse together into liquids. 
5. The rate of diffusion of liquids is higher than that of solids. This is due to the fact that in the liquid state, Particles move freely and have greater space between each other as compared to particles in the solid state.

The gaseous state 

1. Gases are highly compressible as compared to solids and liquids. 
2. The liquefied petroleum gas (LPG) or the oxygen supplied to hospitals in cylinders is compressed gas. 
3. Compressed natural gas (CNG) is used as fuel these days in vehicles. 
4. Due to its high compressibility, large volumes of a gas can be compressed into a small cylinder and transported easily.
5. Due to the high speed of particles and the large space between them, gases show the property of diffusing very fast into other gases.
6. In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container.

Can matter change its state?

We all know that water can exist in three states of matter

• solid, as ice,
• liquid, as water, and
• gas, as water vapour

Effect of change in temperature 

On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating at a greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid. 

Melting Point

• The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
• The melting point of a solid is an indication of the strength of the force of attraction between its particles.
• The melting point of ice is 273.15 K. 
• The process of melting, that is, the change of a solid state into a liquid state, is also known as fusion.
• When a solid melts, its temperature remains the same.

The heat gets used up to change the state by overcoming the forces of attraction between the particles. As this heat energy is absorbed by ice without showing any rise in temperature, it is considered that it gets hidden into the contents of the beaker and is known as the latent heat. The word latent means hidden. 

Latent heat of fusion- The amount of heat energy that is required to change 1kg of solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion.

Particles in water at 0°C have more energy as compared to particles in ice at the same temperature.

When we supply heat energy to water, particles start moving even faster. At a certain temperature, a point is reached when the particles have enough energy to break free from the forces of attraction of each other. At this temperature, the liquid starts changing into gas. The temperature at which a liquid starts boiling at the atmospheric pressure is known as it's boiling point. Particles from the bulk of the liquid gain enough energy to change into the vapour state. 

For water this temperature is 373 K.

Particles in steam, that is, water vapour at 373 K have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporisation.

The state of matter can be changed into another state by changing the temperature.

We know that there are substances which change state from solid to liquid and from liquid to gas on application of heat. There are also some substance that change directly from a solid state to a gaseous state and vice versa without changing into the liquid state.

Camphor or ammonium chloride can change its state directly from solid to gas without changing into a liquid state. A change of state directly from solid to gas without changing into a liquid state is called sublimation, and the direct change of gas to solid without changing into a liquid is called deposition.

Effect of change of pressure

• If we apply pressure and reduce the temperature of gases, we can liquefy gases.
• We can store carbon dioxide in a solid state under high pressure. When the pressure decreases to 1 atmosphere, solid CO2 is converted directly to a gaseous state without becoming liquid. This is why solid carbon dioxide is also known as dry ice.
• Pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas.

Evaporation

The phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.

Factors affecting evaporation

The rate of evaporation increases with 

1. An increase in surface area- Evaporation is a surface phenomenon. If the surface area is increased, the rate of evaporation increases
2. An increase in temperature- With the increase in temperature, a greater number of particles get enough kinetic energy to go into the vapour state.
3. A decrease in humidity- The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in the air is already high, the rate of evaporation decreases.
4. An increase in Wind speed- With the increase in wind speed, the particles of water vapour move away with the wind. This phenomenon decreases the amount of water vapour in the surroundings.

Q. How does evaporation cause cooling?

    In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy from the surroundings to regain the energy lost during evaporation. This absorption of energy from the surroundings make the surroundings cold.

What happens when you pour some acetone (nail polish remover) on your palm? The particles gain energy from your palm or surroundings and evaporate causing the palm to feel cool.

After a hot sunny day, people sprinkle water on the roof or open ground because the large latent heat of vaporisation of water helps to cool the hot surface.

Q. Why should we wear cotton clothes in summer?

    During summer, we perspire more because of the mechanism of our body which keeps us cool. We know that during evaporation, the particles at the surface of the liquid gain energy from the surroundings or body surface and change into vapour. The heat energy equal to the latent heat of vaporisation is absorbed from the body leaving the body cool. Cotton,being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation.

Q. Why do we see water droplets on the outer surface of a glass containing ice-cold water?

    Let us take some ice-cold water in a tumbler. Soon we will see water droplets on the outer surface of the tumbler. The water vapour present in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state, which we see as water droplets.

THE FUNDAMENTAL UNIT OF LIFE

MOTION

Motion- Motion is the change in position of an object with respect to time and its surroundings.

motion along a straight line

Uniform motion and Non-Uniform motion

Measuring the rate of motion

rate of change of velocity

graphical representation of motion

Distance Time graph 

velocity time graph 

Equation of motion by graphical method 

UUniform circular motion