Chapter 15 — Air Around Us

What is Air?

Air is the invisible mixture of gases that fills the space around the Earth and reaches up in layers to form the atmosphere. Even though we cannot see air with our eyes, we can feel it when it moves as wind, hear it when it makes sounds, and observe its effects on objects like leaves, flags and kites. Air surrounds all living things and is present in the empty spaces of objects such as bottles and balloons.

Air acts as a protective blanket for the planet. The atmosphere made of air reduces extremes of temperature between day and night and screens harmful parts of the Sun’s radiation. Air also contains tiny water droplets or vapour that help form clouds and rain. Dust and other particles are mixed into air and travel with it. The amount and type of these particles change from place to place and at different times.

When we study air, we learn simple observable properties: it occupies space, it has weight, and it exerts pressure. Each of these properties can be shown using safe classroom activities like inflating a balloon, using a balance with balloons, or observing water movement under an inverted glass. We also learn how air supports important processes such as breathing, burning and plant growth. Understanding air helps in everyday life — from knowing why we feel cold on windy days to why breathing clean air is vital for health.

Studying air builds the foundation for later topics in weather, environmental science and physics. Students are encouraged to be curious: try experiments, make careful observations, and draw diagrams. Simple notes and drawings will help remember that although air is invisible, its presence and behaviour affect everything around us.

Composition of Air

Air is not a single gas but a mixture of several gases and tiny particles. The main component is nitrogen, which forms the largest part of air. Oxygen is the second most abundant gas and is vital for breathing and burning. Apart from these two, there are small amounts of other gases such as argon, neon, helium and carbon dioxide. The amount of water vapour in air changes from place to place and with temperature — this is what we call humidity. Additionally, dust, pollen, soot and tiny droplets are mixed with the gases.

The approximate composition of dry air is commonly given as roughly 78% nitrogen and 21% oxygen, with the remaining 1% made up of argon, carbon dioxide and other trace gases. Carbon dioxide is present in small amounts but plays an important role because plants use it to make food during photosynthesis. Argon and other noble gases are chemically inert and do not react easily. Water vapour is not constant; warm air can hold more water vapour than cold air.

Human activities change the composition locally and sometimes globally. Burning fossil fuels increases carbon dioxide and releases other harmful gases and fine particles. Farming, factories and vehicles add to the small components in air. Natural processes like volcanic eruptions and plant respiration also add gases and particles.

Classroom activities can help students identify gases. A glowing splint that bursts into flame shows oxygen. Bubbling breath through limewater turning it milky indicates carbon dioxide. Simple charts and diagrams are useful tools to remember the different components and how their amounts affect breathing, burning and weather. Observing how air composition varies helps students understand environmental and health issues linked to poor air quality.

Air Occupies Space

Even though air is invisible, it fills up space. You can show this by many easy experiments. For example, when you blow up a balloon the balloon becomes larger because air fills its inside volume. The balloon keeps its shape only because air pushes outward from inside. Another experiment is to hold a glass upside down and push it into a bowl of water. You will see air trapped inside the glass as bubbles or as a space where water does not enter. This trapped air occupies that part of the glass.

A syringe without a needle also demonstrates this property. When you pull the plunger, air fills the larger space and the plunger moves back in. If you block the nozzle and try to pull further, you feel resistance because the amount of air in the syringe cannot expand freely. The resistance shows that air occupies a definite volume and resists changes when confined.

Understanding that air occupies space helps in many everyday situations. For example, empty bottles and containers still have air inside unless they are vacuum-packed. When you dive under water you see bubbles of air escaping from your mouth or nose — those bubbles are air occupying and leaving the underwater space. Toys and tools such as air pumps, syringes, sports balls and balloons work because air takes up space in them.

These experiments are safe and can be done in class with guidance. Students should note observations carefully: what changes when air is allowed to move and what remains when it is trapped. Drawing diagrams of each setup helps to remember the steps and the idea that even though we cannot see air, it occupies space and affects how objects behave.

Air Has Weight

Air is made of tiny particles that have mass. Although each particle is very light, a large number of them together make the air have weight. You can notice this in simple class activities. For instance, take two identical balloons and inflate only one. Use a balance or make a simple weighing device: the side with the inflated balloon will be slightly heavier than the deflated one. The extra weight comes from the mass of the air you put into the balloon.

Another way to feel that air has weight is to use two sealed containers of the same size and material. One container may have more air pressure inside (if compressed) while the other has normal air; measuring carefully you will find a slight difference in weight. Although these differences are small for small volumes, the entire atmosphere above us has very large total weight. That weight of the column of air above a place is what creates atmospheric pressure.

This idea of air weight explains some observations in nature. At higher altitudes, there is less air above and therefore less weight pressing down; we say the air pressure is lower. Weather balloons must overcome the weight of air as they rise. Airplanes and hot-air balloons are designed considering the mass of air they displace or carry. Even everyday tools like a compressed air can or a filled football weigh more than their empty versions because of the air inside.

When doing experiments, students should note that measuring the weight of air requires sensitive scales, but simple classroom demonstrations are clear enough to build the idea. Always follow safety instructions and have an adult when working with sharp instruments or pressurised containers.

Air Exerts Pressure

Air does not only have weight; it pushes on everything around it. This push is called air pressure. Air pressure exists because air particles move and strike surfaces in all directions. When many particles hit an area, they exert a force on that area. We feel the result of air pressure in many ways: when we hear wind pushing against a door, when our ears ‘pop’ during a change in height, or when a suction cup sticks to a smooth surface.

Simple experiments can show air pressure clearly. One classic demonstration is to fill a glass with water, cover it with a card, and then turn the glass upside down while holding the card in place. When the hand is removed, the card stays in place because air pressure from outside the glass pushes upward on the card more than the weight of the water pulls it down. Another experiment is to light a candle and cover it with an inverted jar. As the flame uses up oxygen inside, the pressure drops slightly and water may rise into the jar if placed in a shallow dish — showing the effect of changing air pressure.

Air pressure also changes with altitude and temperature. At higher places there is less air above, so the pressure is lower. Warm air tends to rise and create lower pressure areas; cooler air sinks and creates higher pressure areas. These differences in pressure cause air to move from high to low pressure regions — that movement is wind. Devices such as pumps, syringes and vacuum cleaners work because they create pressure differences that move air or fluids.

Students should try safe classroom activities to observe pressure and record what happens. Drawing forces on diagrams helps understand why a card stays in place or why suction cups stick. Learning about air pressure is a key step to understanding weather, sound, and many machines that use air.

Role of Air in Breathing

Breathing is the process by which living organisms exchange gases with their surroundings. Air supplies the oxygen our bodies need to burn food and produce energy. When we inhale, air enters through the nose or mouth, goes down the windpipe and reaches the lungs. Inside the lungs are tiny air sacs called alveoli where oxygen passes into the blood and carbon dioxide, a waste gas from the body, passes out of the blood into the lungs to be exhaled.

Different animals have different breathing systems, but all need air in some form. Humans and many animals rely on oxygen from air at or near the Earth's surface. Plants also interact with air: during the day they take in carbon dioxide for photosynthesis and give out oxygen, which helps balance gases in the atmosphere. At night some plants may respire like animals and release carbon dioxide.

There are simple classroom activities that illustrate the role of air in breathing. Bubbling exhaled air through limewater makes the water turn milky because of the carbon dioxide in breath. Counting breaths before and after exercise shows how physical activity raises the breathing rate and depth because muscles need more oxygen. Observing how smoke or dusty air makes breathing harder helps students understand health risks from polluted air.

Good breathing depends on clean air. Pollutants such as smoke, dust and harmful gases can damage lungs and reduce the ability to take in oxygen. Teaching hygiene, avoiding smoky environments, and improving indoor ventilation are practical steps to protect breathing. Students should learn to record breathing patterns, try simple tests under supervision, and appreciate the link between air quality and health.

Air and Combustion

Combustion or burning is a chemical process in which substances combine with oxygen and release heat and light. Air contains oxygen, so it supports burning. In everyday life we see combustion when wood burns in a fire, gas burns on a stove, or candles burn. If oxygen is removed, burning stops. This important link between air and combustion can be shown by simple classroom demonstrations carried out safely under adult supervision.

One common experiment is to light a candle and cover it with a jar. The flame will burn for a short time and then go out because it uses up the oxygen inside the jar. This shows that air supports the flame. Another demonstration is to blow on some glowing charcoal — the flame becomes brighter because the blow brings more oxygen to the burning material. Fire spreads more quickly where there is a steady supply of air; in enclosed spaces fires may grow more slowly if oxygen is limited.

Knowing how air affects combustion helps with fire safety. Smothering a small fire by covering it cuts off oxygen and can safely put out flames. Removing heat or separating fuel also stops fire. On the other hand, strong drafts or winds can make a small ember grow into a larger fire by supplying fresh oxygen. In engines and stoves, the right mix of fuel and air is important for clean and efficient combustion; too little air causes incomplete burning and more smoke.

Students should learn both the science and safety: never play with matches, always have adult supervision for experiments, and know how to report and respond to dangerous fires. Understanding air's role in combustion links to practical issues like cooking, engines and controlled burning in agriculture.

Air Helps in Sound and Smell

Air plays an important role in how we hear sounds and smell things. Sound travels through a material medium by vibrations; in everyday life that medium is usually air. When an object vibrates — for example, a drum skin or a guitar string — it makes nearby air particles vibrate too. These vibrations travel as waves through the air until they reach our ears and are detected by the auditory system. If there is no air, sound cannot travel, which is why a bell placed in a vacuum becomes almost silent as the air is removed.

Smell works because tiny molecules from substances mix with air and travel to the nose. When food is cooked, molecules rise with warm air and reach our nose, allowing us to smell the aroma. Wind carries odours over long distances; a pleasant smell from a flower garden can be noticed far away if the wind carries the scent. Similarly, harmful smells from factories or garbage can spread and cause discomfort or health problems for people downwind.

Classroom experiments can demonstrate these ideas. A ringing bell inside a jar connected to a pump will become fainter as the air is pumped out. Another simple activity is to place a scented cloth at one end of a tube and ask students to detect the smell at the other end by blowing air through — this shows that smell moves with air flow. Observing how sounds change in different rooms, or how smells are stronger near a source, helps students connect experience with these scientific ideas.

Learning that air carries sound and smell has practical uses: designing quiet rooms and auditoriums, ventilating kitchens, and controlling odours near schools and homes. It also reinforces why keeping air clean is essential for comfort and health.

Air and Weather: Wind Formation

Wind is the movement of air from one place to another. It happens because the Sun heats different parts of the Earth unevenly. Land, water, and air warm up at different rates. When air over a place becomes warm, it becomes lighter and rises, leaving an area of lower pressure. Cooler air from nearby higher pressure areas moves in to take its place. This movement of air is what we feel as wind.

Local features affect wind. For example, during the day sunlight heats land faster than sea. The warm air over the land rises and cooler air from the sea moves inland — this movement is called a sea breeze. At night the land cools faster than the sea, causing cool air to move from land to sea — a land breeze. Hills, buildings and forests change the speed and direction of wind by blocking or channeling it.

On larger scales, pressure differences across regions lead to more steady winds like the monsoon winds or trade winds. Seasonal heating patterns and the rotation of the Earth influence these large movements. Weather systems are linked to pressure changes: areas of low pressure often bring clouds and rain because rising warm air cools and its water vapour condenses to form clouds. Areas of high pressure often bring clear skies.

Students can observe wind with simple tools like a pinwheel, wind vane or by watching flags and leaves. Recording wind direction and strength over days helps understand patterns. Predicting weather uses measurements of wind, temperature and pressure. Understanding how wind forms connects everyday observations — a breezy day or a gust — to larger forces working in the atmosphere.

Air Pollution and Its Causes

Air pollution occurs when harmful substances or excessive quantities of natural substances are mixed into the air. Pollutants include gases such as carbon monoxide, sulfur dioxide, nitrogen oxides, and volatile organic compounds; tiny solid or liquid particles called particulate matter (dust, soot); and smoke or chemical fumes. These pollutants can come from human activities as well as natural events.

Major human causes include vehicle exhaust from cars, trucks and buses; smoke from burning biomass like wood and crop residue; emissions from factories and power plants that burn coal or oil; dust from construction and mining; and burning plastic or other waste. Indoor pollution can come from poorly ventilated stoves and heaters. Natural sources include volcanic eruptions, forest fires and dust storms.

Some pollutants are visible, like smoke and dust, but many are invisible and still harmful. For example, carbon monoxide is colourless and odourless yet dangerous because it reduces the blood’s ability to carry oxygen. Tiny particles (PM2.5 and PM10) can enter deep into the lungs and cause health issues. Certain gases can react in the air to form smog or acid rain, which harms plants, buildings and water bodies.

Understanding causes helps us think of solutions: controlling vehicle emissions, using cleaner fuels, reducing open burning and installing filters in factories can all reduce pollution. At home, better ventilation and cleaner stoves reduce indoor pollution. Teaching students to observe visible pollution sources in their neighbourhood helps them connect local problems with global impacts and encourages community action.

Effects of Air Pollution on Health and Environment

Air pollution affects people, plants, animals and buildings. Short-term exposure to polluted air can cause irritation of the eyes, nose and throat, coughing, headaches and breathing difficulty. Long-term exposure increases the risk of chronic respiratory diseases such as asthma, bronchitis and emphysema, and can affect the heart and blood vessels. Children, elderly people and those with pre-existing health problems are especially vulnerable.

Air pollution also damages the environment. Pollutants like sulfur dioxide and nitrogen oxides can combine with water vapour to form acid rain, which harms crops, forests and freshwater bodies. Soot and particulate matter settle on leaves and reduce the sunlight available for photosynthesis, thereby lowering plant growth and crop yields. Ozone near the ground, produced by reactions between pollutants and sunlight, can damage plant tissues and reduce agricultural productivity.

Animals and aquatic life suffer when polluted air leads to polluted waterways and soils. Visibility in cities reduces due to smog and fine particles, affecting daily life and transport safety. Buildings and monuments can be corroded by acidic pollutants. Climate change is linked to certain air pollutants like carbon dioxide and methane that trap heat in the atmosphere, altering long-term weather patterns and affecting ecosystems globally.

Reducing these effects requires both individual actions and policy measures. Cleaner fuels, pollution control devices, protected green spaces, and public awareness help reduce harm. Monitoring air quality and taking precautions, such as staying indoors when pollution is high and using masks when necessary, can protect health. Education about these effects helps students become responsible citizens who can take part in improving the environment.

Ways to Reduce Air Pollution

Reducing air pollution requires actions by individuals, communities, industries and governments. At the individual level, using public transport, walking or cycling instead of private cars reduces vehicle emissions. Car-pooling and maintaining vehicles to reduce exhaust also help. At home, using cleaner fuels like LPG instead of wood or coal, and using efficient stoves and good ventilation cuts indoor smoke. Avoiding burning leaves, plastic or trash prevents toxic gases from entering the air.

Schools and communities can organise tree-planting drives and green spaces which trap dust and absorb carbon dioxide. Industries can install filters and scrubbers to limit the release of smoke, particulates and harmful gases. Switching to cleaner energy sources such as electricity from renewable sources, solar cookers or biogas reduces dependence on polluting fuels. Cities can promote public transport, design better traffic flow and encourage electric vehicles to cut pollution.

Simple classroom projects help students learn and spread awareness: measuring traffic near school, making posters, and calculating pollution reduction from walking or cycling. Policies such as emission standards, regular vehicle checks and waste management rules are important at the government level. Community behaviour change, like proper waste disposal and avoiding open burning, also makes a difference.

Teaching children about practical and low-cost actions empowers them to take part in cleaner-air projects. Small changes by many people add up. When students share knowledge at home, they influence family choices and help build healthier environments for everyone.

Measuring and Observing Air

Although air itself is invisible, its properties can be measured and observed by instruments and by simple classroom tools. Weather stations use thermometers for temperature, anemometers for wind speed, wind vanes for wind direction, and barometers for air pressure. For young students, easy devices and observations give useful information: a pinwheel or wind sock shows wind direction and strength; a thermometer shows how warm or cold the air is; and a simple homemade barometer made from a jar and a stretched balloon can give hints about pressure changes.

Keeping a weather diary is a valuable exercise. Students can make a table with columns for date, time, temperature, wind (calm, breeze, strong), wind direction, sky condition (clear, cloudy, rainy) and notes. Recording the same observations twice daily for a week shows patterns and helps link air temperature and wind with changes in weather. Observing visibility and smelling smoke or odours gives a rough idea of air quality, while more precise measurements need special instruments for particulates and gases.

Classroom experiments can also show air movement and pressure. For example, a homemade barometer uses a balloon stretched over a jar to show slight changes when pressure rises or falls; mark the balloon edge on a scale and note any movement over days. A simple smoke trail from incense can make wind patterns visible near buildings or trees and show how air flows around obstacles. Students should learn to record observations accurately, repeat experiments, and discuss variations.

Building these observation skills prepares students for more advanced study in weather, climate and environmental science. It also helps them understand daily forecasts and the importance of local air quality monitoring. Encourage careful notes, labelled drawings and safe use of tools when performing observations.