Class 8 Science

Here you can find Class 8 Science Notes. These notes include important revision points, simple explanations of “Curiosity”

Chapter 1. Exploring the Investigative World of Science 

This chapter introduces science as a process of investigation, where learning begins with curiosity, careful observation, and meaningful questions. It explains that science is not only about memorising facts but about understanding how knowledge is discovered. The chapter encourages students to ask “why” and “how”, observe everyday events closely, and think like young scientists. It highlights the importance of systematic investigation, where one factor is changed at a time, results are observed carefully, and conclusions are drawn logically. Through simple real-life examples, the chapter shows how scientific thinking helps us explore both small everyday phenomena and big challenges related to Earth and life.

Key Points

• Science begins with curiosity and asking thoughtful questions.

• Observation is the first step in understanding the world around us.

• Science is an evolving subject where answers often lead to new questions.

• Investigation in science involves planning, experimenting, and explaining results.

• A good scientific investigation changes only one factor at a time.

• Keeping records and notes helps in analysing observations accurately.

• Experiments do not always need a laboratory; daily-life situations can be investigated scientifically.

• Measurement helps make observations more reliable and comparable.

• Scientific thinking balances careful observation with creative ideas.

• Science helps us understand topics ranging from microorganisms to planet-wide issues.

• Understanding science enables us to face challenges like health, technology use, and climate change.

• Humans play an important role in both causing and solving environmental problems.

• Science guides us to make responsible decisions for the future of Earth.

👉 👉Science is not just a subject but a way of thinking. By being curious, observing carefully, and investigating honestly, we can understand the world better and use scientific knowledge responsibly to protect life and the planet.

Chapter 2. The Invisible Living World: Beyond Our Naked Eye 

This chapter explains that a large part of the living world is invisible to our naked eyes and can be observed only with the help of magnifying lenses and microscopes. It introduces students to the discovery of cells and microorganisms, which form the basic building blocks of life. The chapter describes how scientific tools helped humans explore this hidden world and how these discoveries changed our understanding of living organisms. It also explains the structure of cells, differences between plant and animal cells, and the important roles played by microorganisms in nature, food preparation, agriculture, and environmental balance.

Key Points

• Many living organisms are too small to be seen without special instruments.

• The invention of the microscope opened the study of the invisible living world.

• Cells are the basic unit of life in all plants and animals.

• Robert Hooke discovered cells while observing cork under a microscope.

• Antonie van Leeuwenhoek first observed living microorganisms.

• Cells differ in shape, size, and structure according to their function.

• Plant cells have a cell wall and chloroplasts, while animal cells do not.

• Living beings show levels of organisation: cell → tissue → organ → organ system → organism.

• Microorganisms include bacteria, fungi, protozoa, algae, and viruses.

• Some microorganisms are useful in making curd, bread, and medicines.

• Microorganisms help in decomposition and recycling of nutrients.

• Certain bacteria improve soil fertility through nitrogen fixation.

• Microalgae produce a large amount of oxygen and support life on Earth.

👉 👉The invisible living world shows that even the smallest organisms have great importance. By understanding this hidden life, we learn to respect nature, value scientific discovery, and use microorganisms responsibly for the benefit of humans and the environment.

Chapter 3. Health – The Ultimate Treasure 

This chapter explains that health is much more than just the absence of disease. It highlights that true health includes physical, mental, and social well-being. The chapter discusses how our lifestyle choices, environment, and habits directly affect our health. It explains different types of diseases, their causes, and modes of spread, along with ways to prevent and control them. Special emphasis is given to communicable and non-communicable diseases, the importance of hygiene, balanced diet, exercise, vaccination, and the role of the immune system in protecting our body. Overall, the chapter encourages adopting healthy habits to lead a balanced and happy life.

Key Points

• Health includes physical, mental, and social well-being, not just freedom from illness.

• A healthy person can work efficiently and cope well with daily challenges.

• Lifestyle and environment play a major role in maintaining good health.

• Eating a balanced diet, exercising regularly, and getting enough sleep are essential for health.

• Clean surroundings, safe drinking water, and fresh air help prevent diseases.

• Symptoms are what we feel (pain, tiredness), while signs can be observed or measured (fever, rash).

• A disease affects the normal functioning of the body or mind.

• Communicable diseases are caused by pathogens and can spread from person to person.

• Diseases can spread through air, water, food, direct contact, or insects (vectors).

• Non-communicable diseases do not spread between people and are linked to lifestyle and environment.

• Deficiency diseases occur due to lack of essential nutrients in the diet.

• Prevention is better than cure and simple habits can reduce disease spread.

• The immune system protects the body from harmful pathogens.

• Vaccines train the immune system to fight specific diseases.

• Antibiotics work only against bacterial infections and should be used wisely.

• Misuse of antibiotics can lead to antibiotic resistance, making treatment difficult.

👉 👉Health is our greatest wealth. By adopting healthy habits, keeping our surroundings clean, and using medicines responsibly, we can prevent diseases and lead a balanced, active, and happy life.

Chapter 4. Electricity – Magnetic and Heating Effects 

This chapter explains how electricity is closely connected with magnetism and heat. It shows that when electric current flows through a wire, it creates a magnetic field, which can turn a simple coil into a temporary electromagnet. The chapter also explains that electric current produces heat due to resistance in wires, which is used in many household appliances. In addition, it describes how cells and batteries generate electricity through chemical reactions, and compares voltaic cells, dry cells, and rechargeable batteries. Overall, the chapter helps students understand how electricity works in daily life, from lifting scrap metal to heating food and powering devices.

Key Points

• Electric current flowing through a wire produces a magnetic effect.

• A magnetic field exists around a current-carrying conductor.

• A coil carrying electric current behaves like a magnet.

• Such a current-carrying coil is called an electromagnet.

• An electromagnet has two poles – North and South.

• The strength of an electromagnet depends on current, number of turns, and iron core.

• Polarity of an electromagnet can be reversed by changing current direction.

• Electric current also produces heat due to resistance in wires.

• This is called the heating effect of electric current.

• Appliances like heaters, irons, and kettles work on heating effect.

• Excess heating can cause damage and fire hazards.

• Cells and batteries produce electricity using chemical reactions.

• Voltaic cells use metal plates and liquid electrolytes.

• Dry cells are compact and used in daily devices.

• Rechargeable batteries can be reused multiple times and reduce waste.

👉 👉Electricity is a powerful form of energy that must be used carefully and responsibly. Understanding its magnetic and heating effects helps us use electrical devices safely, save energy, and protect the environment. Scientific knowledge guides us to use technology wisely for a better and sustainable future.

Chapter 5. Exploring Forces  

This chapter explains the concept of force as a push or pull that arises due to interaction between objects. It helps students understand how forces affect the motion, direction, and shape of objects in everyday life. The chapter discusses different effects of force, showing that a force can make an object move, stop, change speed, change direction, or change its shape. It further classifies forces into contact forces and non-contact forces, explaining muscular force, friction, magnetic force, electrostatic force, and gravitational force with simple examples. The chapter also introduces the ideas of weight, gravity, buoyant force, and explains why some objects float or sink in liquids.

Key Points

• A force is a push or pull caused by interaction between objects.

• Force can start or stop motion of an object.

• Force can change the speed of a moving object.

• Force can change the direction of motion.

• Force can change the shape of an object.

• At least two objects must interact for a force to act.

• The SI unit of force is newton (N).

• Contact forces act only when objects are in physical contact.

• Muscular force is applied by muscles of humans and animals.

• Friction is a contact force that opposes motion between surfaces in contact.

• Friction is greater on rough surfaces and less on smooth surfaces.

• Non-contact forces act without physical contact.

• Magnetic force acts between magnets or magnetic materials.

• Electrostatic force acts between electrically charged objects.

• Like charges repel and unlike charges attract each other.

• Gravitational force is the force with which Earth attracts objects.

• Gravity always acts downward and is always attractive.

• Weight is the gravitational force acting on an object.

• Weight is measured in newton (N) using a spring balance.

• Mass is the amount of matter in an object and remains constant everywhere.

• Buoyant force (upthrust) is the upward force applied by a liquid.

• Objects float or sink depending on gravitational force and buoyant force.

👉 👉Forces control motion and stability in our daily lives. By understanding different types of forces and their effects, we learn how nature works and how to use force wisely, safely, and efficiently in science, technology, and everyday activities.

Chapter 6. Pressure, Winds, Storms, and Cyclones  

This chapter explains how pressure is created when a force acts on a surface and how changes in pressure lead to natural phenomena such as winds, storms, and cyclones. It describes pressure as force acting per unit area and shows how pressure depends on the area over which a force is applied. The chapter explores how liquids and air exert pressure in all directions and how differences in air pressure cause winds to flow. It further explains the formation of thunderstorms, lightning, and cyclones, highlighting their causes, effects, and safety measures to reduce damage to life and property.

Key Points

• Pressure is defined as force per unit area.

• Pressure increases when the same force acts on a smaller area.

• Broad straps or handles reduce pressure by increasing the area.

• The SI unit of pressure is pascal (Pa) or N/m².

• Liquids exert pressure at the bottom and on the sides of containers.

• Liquid pressure increases with the height of the liquid column.

• Overhead water tanks are placed at a height to provide greater water pressure.

• Air exerts pressure on all objects; this is called atmospheric pressure.

• Air pressure acts in all directions.

• Air moves from a region of high pressure to low pressure.

• Winds are caused due to differences in air pressure.

• Warm air rises, creating a low-pressure area.

• Cool air moves in to replace warm rising air.

• High-speed winds create low-pressure regions.

• Roofs may be blown off during storms due to pressure differences.

• Storms are caused by strong winds with rain.

• Thunderstorms involve thunder, lightning, and heavy rainfall.

• Lightning is caused by the discharge of electric charges in clouds.

• Lightning conductors protect buildings by safely transferring charges to the ground.

• Cyclones form over warm oceans due to very low pressure and rotating winds.

• The eye of a cyclone is calm, while surrounding areas experience strong winds.

• Weather warnings help reduce loss of life during cyclones.

👉 👉Pressure and air movement play a major role in shaping weather and natural events. By understanding pressure, winds, and storms, we can stay safe, respect nature’s power, and use scientific knowledge responsibly to reduce risks and protect life and property.

Chapter 7. Sound  

This chapter explains sound as a form of energy that helps us hear and communicate. It describes how sound is produced by vibrating objects and how these vibrations travel through a medium in the form of waves. The chapter explains that sound needs a medium like air, water, or solids to travel and cannot move through a vacuum. It also introduces important characteristics of sound such as loudness and pitch, and explains how sound is reflected to produce echoes. The chapter further highlights the usefulness of sound in daily life and the harmful effects of noise pollution on health.

Key Points

• Sound is a form of energy that produces the sensation of hearing.

• Sound is produced due to vibrations of objects.

• Vibrating objects move to and fro rapidly.

• Sound needs a medium to travel

• Sound can travel through solids, liquids, and gases.

• Sound cannot travel in a vacuum.

• Sound travels in the form of waves.

• Loudness depends on the strength of vibrations.

• Loudness is measured in decibel (dB).

• Pitch depends on the speed of vibration.

• Fast vibrations produce high-pitched sound.

• Slow vibrations produce low-pitched sound.

• Echo is the repetition of sound due to reflection from a distant surface.

• Echo can be heard when the reflected sound reaches the ear after a short delay.

• Noise is unwanted or unpleasant sound.

• Continuous loud noise causes noise pollution.

• Noise pollution can lead to stress, headache, hearing loss, and lack of concentration.

• Reducing noise helps protect human health and environment.

👉 👉Sound is essential for communication and daily activities, but excessive noise is harmful. By understanding sound and controlling noise, we can protect our hearing, health, and environment while using science responsibly.

Chapter 8. Nature of Matter – Elements, Compounds, and Mixtures 

This chapter explains that everything around us which has mass and occupies space is called matter. It helps students understand how matter is classified into elements, compounds, and mixtures based on its composition and properties. The chapter describes how substances combine physically to form mixtures while retaining their individual properties, and how elements combine chemically in fixed ratios to form compounds with entirely new properties. It also explains the concept of pure substances, highlights the difference between uniform and non-uniform mixtures, and introduces minerals as natural substances found in the Earth. Through activities and examples from daily life, the chapter shows how knowledge of matter helps in science, technology, industry, and environmental protection.

Key Points

• Matter is anything that has mass and occupies space.

• Most substances around us are made of more than one component.

• A mixture is formed when two or more substances are mixed physically.

• Components of a mixture retain their individual properties.

• Mixtures can be uniform (homogeneous) or non-uniform (heterogeneous).

• Air is a uniform mixture of gases like nitrogen, oxygen, and carbon dioxide.

• Alloys are uniform mixtures of metals or metals with non-metals.

• A pure substance contains only one kind of particle.

• Pure substances cannot be separated by physical methods.

• Pure substances are classified as elements or compounds.

• Elements are the simplest substances and cannot be broken down further.

• Elements are made of identical particles called atoms.

• Compounds are formed when elements combine chemically in a fixed ratio.

• Properties of a compound are different from its constituent elements.

• Water is a compound made of hydrogen and oxygen in a fixed ratio.

• Components of a compound cannot be separated by physical means.

• Minerals are naturally occurring substances found in rocks.

• Minerals can be elements or compounds.

• Knowledge of elements, compounds, and mixtures helps in medicine, agriculture, construction, and industry.

👉 👉Understanding the nature of matter helps us recognise how substances around us are formed and used. By learning the difference between elements, compounds, and mixtures, we can use natural resources wisely, support scientific innovation, and protect the environment for a sustainable future.

Chapter 9. The Amazing World of Solutes, Solvents, and Solutions  

This chapter explains how different substances mix to form solutions and why some mixtures appear uniform while others do not. It introduces the concepts of solute, solvent, and solution using everyday examples like sugar in water and ORS. The chapter also explores how much solute a solvent can dissolve, how temperature affects solubility, and how gases dissolve in liquids. Further, it explains why some objects float or sink by introducing the idea of density, along with methods to measure mass and volume accurately. Through simple activities and real-life connections, the chapter helps students understand the science behind mixing, dissolving, floating, and sinking.

Key Points

• A uniform mixture is called a solution.

• The substance that dissolves is the solute, and the substance that dissolves it is the solvent.

• In a solution, components are evenly distributed and cannot be seen separately.

• Air is a solution of gases where nitrogen acts as the solvent.

• A solution that can dissolve more solute is called an unsaturated solution.

• A solution that cannot dissolve more solute at a given temperature is a saturated solution.

• Solubility is the maximum amount of solute that can dissolve in a fixed amount of solvent at a given temperature.

• Solubility of most solids increases with increase in temperature.

• Solubility of gases decreases when temperature increases.

• Oxygen dissolved in water supports aquatic life.

• Objects float or sink based mainly on their density.

• Density = Mass ÷ Volume.

• Density is independent of shape but depends on temperature and pressure.

• Heating generally decreases density, while cooling increases it.

• Ice floats on water because it is less dense than liquid water.

👉 👉Understanding solutions and density helps us explain many everyday phenomena—from making ORS to why ships float and ice forms on lakes. Scientific thinking allows us to observe carefully, measure accurately, and apply knowledge responsibly in daily life and environmental care.

Chapter 10. Light – Mirrors and Lenses   

This chapter explains how light behaves when it falls on mirrors and lenses and how images are formed. It introduces reflection of light using plane mirrors, concave mirrors, and convex mirrors, and explains their image formation with simple rules. The chapter also discusses refraction of light through lenses, including convex and concave lenses, and their uses in daily life. It highlights important concepts such as real and virtual images, focal length, magnification, and applications of mirrors and lenses in devices like vehicles, spectacles, and scientific instruments.

Key Points

• Light travels in a straight line.

• When light falls on a mirror, it undergoes reflection.

• A plane mirror forms a virtual, erect image of the same size.

• Images formed by a plane mirror show lateral inversion.

• A concave mirror can form both real and virtual images.

• A convex mirror always forms a virtual, erect, and smaller image.

• Concave mirrors are used in torches, headlights, and solar cookers.

• Convex mirrors are used as rear-view mirrors in vehicles.

• Refraction is the bending of light when it passes from one medium to another.

• A convex lens converges light rays and can form real or virtual images.

• A concave lens diverges light rays and forms only virtual images.

• The focal length is the distance between the focus and the mirror or lens.

• Magnification tells how large or small an image is compared to the object.

• Lenses are used in spectacles, microscopes, cameras, and magnifying glasses.

• Understanding light helps in designing optical devices used in daily life.

👉 👉Light helps us see and understand the world around us. By learning how mirrors and lenses work, we can use light wisely to create useful tools that improve safety, learning, and technology in everyday life.

Chapter 11. Keeping Time with the Skies   

This chapter explains how humans have used the sky to understand and measure time since ancient times. It describes how the Moon’s phases, the movement of the Sun, and the revolution of Earth create natural cycles that help define a day, month, and year. The chapter explains why the Moon appears to change shape, how waxing and waning phases occur, and why the Moon is sometimes visible during the day. It also introduces different types of calendars—lunar, solar, and luni-solar—and explains how festivals are connected to astronomical events. The chapter further highlights the importance of artificial satellites and how they help in communication, weather forecasting, and space research.

Key Points

• The Moon does not produce light; it shines by reflecting sunlight.

• The visible shapes of the Moon are called its phases.

• A full cycle of Moon phases takes about 29.5 days.

• Waxing phase occurs when the illuminated part of the Moon increases.

• Waning phase occurs when the illuminated part of the Moon decreases.

• New Moon occurs when the illuminated part is not visible from Earth.

• Full Moon occurs when the entire illuminated part faces Earth.

• The Moon rises about 50 minutes later each day.

• The phases of the Moon are not caused by Earth’s shadow.

• A day is based on Earth’s rotation, a month on Moon’s revolution, and a year on Earth’s revolution around the Sun.

• Lunar calendars are based on Moon phases.

• Solar calendars are based on Earth’s movement around the Sun.

• Luni-solar calendars combine both Moon phases and seasons.

• Many Indian festivals are linked to astronomical events.

• Artificial satellites orbit Earth and help in communication, navigation, and research.

• ISRO satellites support weather monitoring, mapping, and space exploration.

👉 👉Nature follows fixed patterns that help us measure time and understand the universe. By observing the sky carefully and using scientific knowledge responsibly, humans have developed calendars, celebrated cultures, and advanced space technology for the benefit of society.

Chapter 12. How Nature Works in Harmony    

This chapter explains how nature functions as a connected system, where living organisms and non-living elements depend on each other to survive. It shows that plants, animals, microorganisms, air, water, soil, sunlight, and temperature are all linked through interactions that maintain balance in nature. The chapter highlights concepts such as habitats, populations, communities, ecosystems, food chains, food webs, and decomposition. Through real-life examples like pond ecosystems, forests, farming systems, mangroves, and the Sundarbans, it explains how even a small change can disturb the balance of nature. The chapter also stresses the role of humans in protecting ecosystems and adopting sustainable practices for the future.

Key Points

• A habitat is a place that provides suitable conditions for organisms to live.

• Every habitat has biotic components (plants, animals, microorganisms) and abiotic components (air, water, soil, sunlight, temperature).

• A population is a group of the same kind of organisms living in a habitat at a given time.

• A community consists of different populations living together in one habitat.

• Interaction between biotic and abiotic components forms an ecosystem.

• Ecosystems can be terrestrial (forests, grasslands, farms) or aquatic (ponds, rivers, lakes).

• Plants are producers as they make their own food through photosynthesis.

• Animals are consumers and depend on plants or other animals for food.

• Decomposers like bacteria and fungi break down dead matter and recycle nutrients.

• A food chain shows who eats whom in a simple sequence.

• A food web is a network of interconnected food chains.

• Each step in a food chain is called a trophic level.

• Interactions like mutualism, commensalism, parasitism, and competition help maintain balance.

• One small change in an ecosystem can lead to many cascading effects.

• Human activities such as deforestation, pollution, and overuse of resources disturb ecosystems.

• Protected areas help conserve biodiversity and natural balance.

• Sustainable farming and responsible resource use are essential for future survival.

👉 👉Nature works through balance and cooperation. Every organism, big or small, has a role to play. When humans disturb this balance, nature suffers—and so do we. By understanding ecosystems and adopting sustainable and responsible practices, we can protect nature and ensure a healthy future for all living beings.

Chapter 13. Our Home – Earth, a Unique Life-Sustaining Planet   

This chapter explains why Earth is a special planet that supports life. It describes how Earth has the right distance from the Sun, suitable temperature, air, water, and soil, which together make life possible. The chapter highlights the importance of the atmosphere, hydrosphere, lithosphere, and biosphere, and how they interact to maintain balance. It also explains the role of gravity, ozone layer, and natural cycles in protecting life. The chapter encourages responsible use of resources so that Earth remains a healthy home for future generations.

Key Points

• Earth is the only known planet that supports life.

• The right distance from the Sun maintains suitable temperature.

• Presence of liquid water is essential for all living organisms.

• The atmosphere provides oxygen for breathing and carbon dioxide for plants.

• The ozone layer protects Earth from harmful ultraviolet rays.

• Gravity holds air and water on Earth’s surface.

• The lithosphere provides land and minerals needed for life.

• The hydrosphere includes oceans, rivers, lakes, and groundwater.

• The biosphere is the zone where living organisms exist.

• Earth’s rotation causes day and night, while revolution causes seasons.

• Natural cycles like the water cycle maintain balance in nature.

• Plants play a key role in maintaining oxygen–carbon dioxide balance.

• Human activities can disturb Earth’s natural balance.

• Pollution, deforestation, and climate change threaten life on Earth.

• Conservation of resources helps protect our planet.

• Sustainable living ensures Earth remains safe for future generations.

👉 👉Earth is our only home and supports all forms of life. By understanding its uniqueness and using resources wisely, we can protect our planet and ensure a safe and healthy future for all living beings.