CBSE Class 8 Science (Curiosity)

1. Exploring the Investigative World of Science

How scientists investigate

• The Scientific Method – The scientific method is the careful way scientists find out how the world works. Observe something, ask a testable question, make a hypothesis (a clear, testable guess), test it with a fair experiment (change one variable, measure one, keep the rest the same), repeat and record data, analyse it, draw a conclusion and share it so others can check. Results that fail the test are useful too: they send you back to a new hypothesis.

2. The Invisible Living World: Beyond Our Naked Eye

Cells · Microorganisms

• Microorganisms: The Tiny Living Things All Around Us – Microorganisms (microbes) are living things too small to see without a microscope. The main groups are bacteria, fungi, protozoa and algae; viruses are also studied with them but are not cells. Bacteria have no nucleus (prokaryotes); the others have one (eukaryotes). Bacteria multiply by splitting in two, so their number doubles again and again. Most microbes are harmless or helpful: our gut microbiota helps digestion, microbes make curd and bread, recycle dead matter and fix nitrogen. A few are pathogens that cause disease. Antibiotics kill bacteria but not viruses, and misusing them breeds resistant bacteria.

3. Health: The Ultimate Treasure

Health and disease

• Health and Disease – Health is complete physical, mental and social well-being, not just the absence of disease. Communicable diseases are caused by pathogens (bacteria, viruses, fungi, protists) and spread from person to person, through air, water, food, touch or animals. Non-communicable diseases such as heart disease, diabetes, many cancers and high blood pressure do not spread; they are linked to genes, age and lifestyle. We prevent disease with hygiene, clean water, vaccines, a balanced diet, exercise, sleep, not smoking, and regular check-ups and self-checks. Antibiotics kill bacteria but not viruses; misusing them breeds resistant bacteria. Medicines must be taken as the leaflet or doctor says.

4. Electricity: Magnetic and Heating Effects

Magnetic effect of current · Heating effect of current · Batteries

• Magnetic Effect of Electric Current – A wire carrying electric current makes a magnetic field around itself. The field forms circles around a straight wire, becomes nearly straight at the centre of a loop, and is uniform inside a solenoid, which then acts like a bar magnet.
• Electric Cells and Batteries: How a Cell Makes Electricity – An electric cell turns chemical energy into electrical energy. It needs two different metals (electrodes) dipped in a liquid or paste that conducts (the electrolyte). A chemical reaction leaves extra electrons on one metal (the negative terminal); when a wire joins the two terminals, electrons flow through it as an electric current. A battery is two or more cells joined together; in series their voltages add up.

5. Exploring Forces

Forces

• Forces: Pushes and Pulls – A force is a push or a pull between two objects. It is measured in newtons (N). Contact forces need touching (push, friction, normal force, tension, buoyancy); non-contact forces act at a distance (gravity, magnetism, electric). A force is drawn as an arrow: start = point of application, direction, length = size. Forces can change an object's speed, direction or shape. If forces balance, a still object stays still (equilibrium). Forces always come in pairs: if A pushes B, B pushes A back equally (Newton's third law).

6. Pressure, Winds, Storms, and Cyclones

Pressure · Winds, storms and cyclones

• Pressure: Force on Each Square Metre – Pressure is the force acting on each unit of area: P = F ÷ A. Its SI unit is the pascal (1 Pa = 1 N/m²). The same force on a smaller area gives a bigger pressure, which is why pins, knives and nails are sharp, and why tractors and camels have wide feet or tyres. Liquids press in all directions, and their pressure grows with depth (P = ρgh). Gases press because their particles keep hitting the walls; squeezing a gas or heating it raises its pressure. The air around us presses with about 101 kPa. Blood pressure is the pressure of blood on the walls of the arteries.

7. Particulate Nature of Matter

Particles of matter

• The Particle Model of Matter – All matter is made of tiny particles that are always moving. In a solid they are close and only vibrate; in a liquid they are close but slide past each other; in a gas they are far apart and move fast in all directions. Heating gives particles more energy: either they move faster (temperature rises) or the forces between them are broken (the state changes while the temperature stays the same). Gas pressure comes from particles hitting the walls.

8. Nature of Matter: Elements, Compounds, and Mixtures

Classifying matter

Coming soon

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

Solutions and density

• Solutions: How Things Dissolve and How Much Can Dissolve – A solution is a uniform mixture of a solute dissolved in a solvent. In water (an aqueous solution) the solute breaks into particles too small to see, so it never settles and passes through filter paper. Concentration tells how much solute is present (mass % = solute ÷ solution × 100). Solubility is the most that can dissolve in 100 g of solvent at a given temperature; beyond it the solution is saturated. Evaporation, crystallisation and distillation separate solutions.

10. Light: Mirrors and Lenses

Mirrors and lenses

Coming soon

11. Keeping Time with the Skies

Sky and calendars

• The Sun–Earth–Moon System – The Sun is a star; Earth orbits it once in about 365¼ days while spinning once a day, and the Moon orbits Earth once in 27.3 days. The Sun always lights half of the Moon. As the Moon goes round, we see changing amounts of that lit half: the phases, which repeat every 29.5 days. The Moon spins once per orbit, so the same face always points at us. Its gravity (with the Sun's) raises two tidal bulges, giving two high tides a day; spring tides come at New and Full Moon, neap tides at the quarters. A solar eclipse happens when the Moon's shadow falls on Earth (New Moon); a lunar eclipse when the Moon enters Earth's shadow (Full Moon). The Moon's 5° tilted orbit means eclipses do not happen every month. Earth's distance from the Sun, liquid water, atmosphere and magnetic field make it fit for life.

12. How Nature Works in Harmony

Interactions in nature

• Ecosystem, Food Chains and Energy Flow – An ecosystem is all the living things in a place plus the non-living things around them, working together. Energy enters as sunlight, passes one way up a food chain, and only about 10% moves to each next level.

13. Our Home: Earth, a Unique Life Sustaining Planet

Earth supports life

Coming soon