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This PSEB 6th Class Science Notes Chapter 15 Air Around Us will help you in revision during exams.

PSEB 6th Class Science Notes Chapter 15 Air Around Us

→ All living things require air to live.

→ Air is present everywhere around us however we cannot see the air.

→ Our earth is surrounded by a thin layer of air that extends upto many kilometres above the surface of the earth. This is known as the atmosphere.

→ Air is made up of water vapours, Oxygen, Nitrogen, Carbon dioxide, dust, and smoke.

→ Nitrogen and Oxygen are the main constituents of air and are present in large quantities.

→ In the air, nitrogen is 78% and oxygen is only 21%.

→ Oxygen is required for burning.

→ Carbon dioxide is a greenhouse gas.

→ The balance of Oxygen and Carbon dioxide in the atmosphere is maintained by the presence of living organisms (man, animals) and plants.

→ Carbon dioxide is used by plants for producing food by photosynthesis. They release oxygen.

→ Oxygen is consumed by animals and humans for respiration. They produce carbon dioxide.

→ Carbon dioxide is used as a fire extinguisher because carbon dioxide does not support g burning.

→ Air can be compressed and it also exerts pressure.

→ Moving air is called wind.

→ Moving air has the power to rotate a windmill which produces electricity.

→ Windmills are very useful as they produce electricity.

→ Air helps in the dispersal of seeds, pollens, and movement of sailing boats, yachts, gliders, aeroplanes, etc.

→ Dispersal of pollens is known as pollination.

→ Ozone present in the upper layer of the atmosphere protects us from the UV rays of the sun.

→ Air: It is a mixture of many gases like nitrogen, oxygen, carbon dioxide, water vapours, etc.

→ Wind: The moving air is wind.

→ Windmill: A device that is being rotated by air and is used for producing electricity.

→ Atmosphere: The thin blanket of air surrounding the earth constitutes the atmosphere.

This PSEB 6th Class Science Notes Chapter 14 Water will help you in revision during exams.

PSEB 6th Class Science Notes Chapter 14 Water

→ Water is a vital resource and is considered a boon to live.

→ Water is present all over the earth.

→ Around the 3/4th part of the earth, the surface is covered with water.

→ The human body consists of 70% of water.

→ We need water for our daily activities and for producing other things.

→ Two main sources of water are surface water and groundwater.

→ Water exists in three states i.e. solid, liquid, and gas.

→ We get water from ponds, lakes, rivers, wells, etc.

→ Sea or Ocean water is salty. It is not fit for drinking and for domestic, agricultural, and industrial needs.

→ As water is a vital resource so it must be conserved.

→ Judicious use of water and saving it is conservation of water.

→ Rainwater is a pure form of water and is safe for drinking.

→ Rainwater harvesting is a technique that conserves water by storage of rainwater. This water can be reused for different useful purposes.

→ The water cycle is a cyclic process in which water is circulated between the earth and the atmosphere.

→ Ocean water supplies water to the water cycle and thus plays an important role.

→ Water from oceans, lakes, wet clothes and plants gets evaporated.

→ Clouds are just the condensation of evaporated water in the air.

→ Clouds cause rains and water returns to earth, oceans, lakes, etc.

→ Snow on mountains melts and water runs into rivers.

→ Water is also absorbed by the ground and becomes available to us as groundwater.

→ Heavy rains and no rains cause too many problems.

→ Heavy rains cause floods which destroy lives and properties.

→ Overflow of water in a large amount beyond its normal limits is known as a flood.

→ A flood is a natural disaster.

→ No rain or very little rain in a region is caused by the drought.

→ In drought conditions availability of food, fodder, and water become negligible.

→ With the increase of population, industries, and agriculture also increase which lay stress on the use of water.

→ Melting: The process of conversion of solid into liquid is called melting.

→ Freezing: The process of converting liquid into solid is called freezing.

→ Evaporation: The process of converting liquid into its vapours is called evaporation.

→ Transpiration: The process by which plants lose their water in the air is called transpiration.

→ Condensation: The process of conversion of water vapours into water is called condensation.

→ Precipitation: Falling of water in the form of rain and snow is called precipitation.

→ Clouds: The condensed water droplets join together to form clouds.

→ Water cycle: The evaporation of water to air, formation of clouds by condensation, and falling of rain on the earth constitutes the water cycle in nature.

→ Rainwater harvesting: Collection of rainwater for use at a time when it is not available otherwise is rainwater harvesting.

This PSEB 6th Class Science Notes Chapter 13 Fun with Magnets will help you in revision during exams.

PSEB 6th Class Science Notes Chapter 13 Fun with Magnets

→ Magnetite is a natural magnet.

→ Some rocks have the property of attracting pieces of iron and these are called natural magnets.

→ Magnet has the property of attracting iron, cobalt, and nickel. Such substances are called magnetic substances.

→ Every magnet has two poles:

• North Pole
• South pole

→ A freely suspended magnet sets itself in a North-South direction.

→ Unlike (opposite) poles of two magnets attract each other whereas like poles repel each other.

→ Man-made magnets are called artificial magnets.

→ Magnets made from iron pieces are called artificial magnets.

→ Magnets are of different shapes such as Bar magnet, Horseshoe shaped (U-shaped) magnet, cylinderical magnet, or spherical magnet.

→ Compass is used to find direction.

→ When a magnet is brought near a compass, its needle gets deflected.

→ On heating a magnet, striking it with a hammer, or dropping it from a height it loses its property of magnetism.

→ If a magnet is not properly stored then it loses its property with time.

→ To store bar magnets with safety the opposite poles of two magnets are placed facing each other.

→ The magnet should be kept away from cassettes mobiles, TVs, CDs, and computers, etc.

→ Compass: Compass is a device that is needed to determine direction.

→ Magnet: Such substances which have the property of attracting iron are called magnets.

→ Magnetite: Magnetite is a natural magnet that was first discovered by a Shepherd named Magnus.

→ North pole: That end of a freely suspended magnet that points towards the geographical north direction is called its North pole.

→ South pole: That end of a freely suspended magnet that points towards the geographical south direction is called its South pole.

This PSEB 6th Class Science Notes Chapter 6 Changes Around Us will help you in revision during exams.

PSEB 6th Class Science Notes Chapter 6 Changes Around Us

→ Change is an act by which a thing becomes different from its previous one.

→ We see many changes around us and every change is important in a positive or negative way.

→ Changes can be grouped together by finding similarities and differences between them.

→ All the changes can be broadly divided into two types i.e. natural and manmade.

→ Changes that occur in nature and do not require our involvement are called natural changes. These are never ending changes.

→ Examples of natural changes include melting of snow, falling of leaves from trees, etc.

→ Changes occurring due to the efforts of human beings are called artificial or manmade changes.

→ Examples of manmade changes include preparing chapattis from wheat flour, cooking vegetables, etc.

→ Based on the speed, we can classify changes into two categories. These are slow changes and fast changes.

→ Slow changes are those which take more time to happen. For example, growing of tree, a baby becoming an adult, etc.

→ Fast changes are those that happen very fast. For example, burning of match sticks, bursting of crackers, etc.

→ Out of all the changes around us, only a few changes can be reversed. These are called reversible changes.

→ The changes which cannot be reversed are called irreversible changes.

→ A change in a substance is called reversible if we can get the substance in its original form by changing the conditions.

→ For example, ice changes to water on melting and water can be changed into ice by cooling, is a reversible change.

→ A change in a substance is called irreversible if we cannot get the substance in its original form by changing the conditions.

→ For example, roti once prepared on Tawa, cannot be changed back to dough again.

→ Some changes are periodic whereas others are non-periodic.

→ Changes that are repeated after regular intervals of time are called periodic changes.

→ For example, change of day and night, swinging of pendulum of a clock, the beating of heart, change of seasons.

→ Changes that are not repeated after a regular interval of time are called non-periodic changes.

→ For example, the occurrence of earthquakes, the occurrence of rain, etc.

→ We have classified changes into physical and chemical changes.

→ Any temporary change in which no new substance is formed and the chemical composition of the original substance remains the same is known as physical change.

→ During physical changes, physical properties like colour, shape, size, state, etc. may change. Therefore, we can say that Physical change is a reversible change.

→ Any permanent change in which new substances are formed. These have physical and chemical properties completely different from those of the original substance.

→ Physical changes are mostly reversible in nature whereas chemical changes are mostly irreversible changes.

→ Expansion and contraction are physical changes that are very useful in our daily life.

→ In the expansion the dimensions of the substance increase and in contraction the dimensions of the substance decrease.

→ Change: An act by which a thing becomes different from its previous one.

→ Natural changes: Changes that are occurring naturally and are never-ending are called natural changes.

→ Manmade changes: Changes that are occurring due to the efforts of human beings are called manmade changes.

→ Periodic change: Changes that are repeated after regular intervals of time are called periodic changes.

→ For example, change of day and night, swinging of pendulum of a clock, beating of heart, change of seasons.

→ Non-periodic changes: Changes that are not repeated after regular intervals of time are called non-periodic changes.

→ For example, the occurrence of earthquakes, the occurrence of rain, etc.

→ Reversible change: The changes which take place in a substance and can be reversed to their original state are called Reversible changes.

→ Irreversible change: The changes which cannot be reversed to the original substances are called Irreversible changes.

→ Physical Change: Physical change is a temporary change in which no new substance is formed and the chemical composition of the original substance remains the same.

→ Chemical change: Chemical change is a permanent change in which new substances are formed whose physical and chemical properties are completely different from those of the original substance.

→ Expansion: When a substance increases its size on heating then the change is called expansion.

→ Thermal expansion: When the expansion is due to an increase in temperature it is called thermal expansion.

→ Contraction: When a substance decreases its size on cooling then the change, is called contraction.

→ Evaporation: When a liquid changes into the gaseous form on heating or on decreasing pressure then the process is known as evaporation.

→ Melting: When a solid changes into liquid form on heating or on increasing pressure then the process is known as melting.