Tamil–English Science Glossary

A push or pull that can change the shape, speed, or direction of an object.

The ability to do work or cause change. Energy cannot be created or destroyed, only converted from one form to another.

The speed of an object in a specific direction. Unlike speed, velocity includes direction.

The rate at which velocity changes over time. An object accelerates when it speeds up, slows down, or changes direction.

The amount of matter contained in an object. Mass stays the same everywhere — on Earth, the Moon, or in space.

The gravitational force acting on an object's mass. Weight changes depending on the strength of gravity.

A force that opposes the motion of objects sliding against each other. Rough surfaces create more friction than smooth ones.

An attractive force between any two objects with mass. The larger the mass, the stronger the gravitational pull.

The amount of force applied per unit area. Pressure = Force ÷ Area.

The amount of mass packed into a given volume. Density = Mass ÷ Volume.

The upward force exerted by a fluid on an object placed in it. Objects float when buoyancy equals their weight.

Work is done when a force causes an object to move in the direction of the force. Work = Force × Distance.

The rate at which work is done or energy is transferred. Power = Work ÷ Time. Measured in Watts (W).

A measure of how hot or cold something is, representing the average kinetic energy of particles. Measured in Celsius (°C) or Kelvin (K).

The distance between two consecutive peaks (or troughs) of a wave. Shorter wavelengths mean higher frequency.

The smallest particle of a chemical element that still has the properties of that element. Made of protons, neutrons, and electrons.

Two or more atoms chemically bonded together. Molecules are the smallest unit of a compound or element that can exist independently.

A pure substance made of only one type of atom. Elements cannot be broken down into simpler substances by chemical reactions. There are 118 known elements.

A substance formed when two or more different elements are chemically combined. The properties of a compound are different from its individual elements.

Two or more substances combined physically but not chemically. The substances in a mixture can be separated by physical methods.

A homogeneous mixture where one substance (solute) is dissolved in another (solvent). The mixture looks uniform throughout.

A substance with a pH below 7 that tastes sour and can react with metals. Strong acids are corrosive and dangerous.

A substance with a pH above 7 that tastes bitter and feels slippery. Bases neutralise acids.

A process in which substances (reactants) are changed into different substances (products). New chemical bonds are formed or broken.

A chemical process where a substance loses electrons or gains oxygen. Rusting of iron is a common example of oxidation.

A rapid chemical reaction between a fuel and oxygen that releases heat and light energy. This is what happens when things burn.

A substance that speeds up a chemical reaction without being used up or changed permanently in the process.

The basic structural and functional unit of all living things. Every living organism is made of one or more cells.

The control centre of a cell that contains the genetic material (DNA). It directs cell activities and reproduction.

The process by which green plants use sunlight, water, and carbon dioxide to make their own food (glucose) and release oxygen.

The process by which living cells break down glucose using oxygen to release energy. Carbon dioxide and water are released as byproducts.

The biological process by which organisms produce offspring of the same species. Can be sexual (two parents) or asexual (one parent).

The passing of traits and characteristics from parents to their offspring through genes. This is why children often look like their parents.

A community of living organisms (plants, animals, microbes) interacting with each other and with their non-living environment (air, water, soil).

A sequence showing who eats whom in an ecosystem. Energy flows from producers (plants) through consumers to decomposers.

A feature or behaviour of an organism that helps it survive and reproduce in its environment. Adaptations develop over many generations.

The process of gradual change in the characteristics of a species over many generations, driven by natural selection.

The natural environment where an organism lives and finds the food, water, and shelter it needs to survive.

A thin, flexible layer that surrounds cells or organelles, controlling what passes in and out.

The green pigment found in plant cells that absorbs sunlight for photosynthesis. It is what makes plants look green.

Any individual living thing — from the smallest bacterium to the largest whale. All organisms grow, respond to the environment, and reproduce.

A group of organisms that share similar characteristics and can breed with each other to produce fertile offspring.

The layers of gases surrounding the Earth, held in place by gravity. It protects us from harmful solar radiation and contains the air we breathe.

The wearing away and transportation of rocks, soil, and sediment by natural forces such as wind, water, ice, or gravity.

Small particles of rock, sand, clay, or organic matter that have been moved from one place and deposited by water, wind, or ice.

The preserved remains, impressions, or traces of ancient organisms found in rock. Fossils help scientists understand life on Earth millions of years ago.

Large, slow-moving sections of Earth's crust and upper mantle. Their movement causes earthquakes, volcanoes, and the formation of mountains.

A sudden shaking of the ground caused by the movement of tectonic plates or volcanic activity. Measured using the Richter scale.

An opening in Earth's crust through which hot molten rock (magma), ash, and gases can escape from deep inside the Earth.

The continuous movement of water through the environment — from oceans and lakes (evaporation), to clouds (condensation), to rain (precipitation), and back again.

The curved path that an object takes around another object in space due to gravity. Planets orbit the Sun; moons orbit planets.

Any object that orbits a larger body in space. Natural satellites (like the Moon) orbit planets; artificial satellites are human-made objects orbited for communication, weather, or navigation.

A massive system of stars, gas, dust, and dark matter held together by gravity. Galaxies can contain billions to trillions of stars.

A massive ball of hot plasma (mainly hydrogen and helium) that produces energy through nuclear fusion in its core. The Sun is the nearest star to Earth.

The distance that light travels in one year — approximately 9.46 × 10¹² km (about 9.46 trillion km). Used to measure vast distances in space.

A region in space where gravity is so strong that nothing — not even light — can escape from it. Formed when massive stars collapse at the end of their lives.

Our Sun and all the objects that orbit it — including 8 planets, their moons, asteroids, comets, and dwarf planets — held together by the Sun's gravity.

A small icy body in space that develops a bright tail of gas and dust when it passes close to the Sun. The tail always points away from the Sun.

The variety of life on Earth — including all species of plants, animals, fungi, and microorganisms — and the variety of ecosystems they form.

The introduction of harmful substances or contaminants into the environment (air, water, or soil) that cause damage to living organisms and ecosystems.

An organism that makes its own food using sunlight (photosynthesis) or chemical energy. Producers form the base of every food chain.

An organism that breaks down dead organic matter (dead plants and animals) into simpler substances, recycling nutrients back into the soil.

The process by which carbon moves through the Earth's systems — from the atmosphere to living things through photosynthesis, and back to the atmosphere through respiration, decomposition, and combustion.

Long-term shifts in global temperatures and weather patterns. While some climate change is natural, since the 1800s human activities (mainly burning fossil fuels) have been the main driver.

A complex network of interconnected food chains showing how energy flows through an ecosystem. More realistic than a single food chain because most organisms eat many different things.

The protection and careful management of natural resources, wildlife, and ecosystems to prevent loss of biodiversity and maintain healthy environments for future generations.

Vibrations that travel as waves through a medium; requires a medium (unlike light).

Electromagnetic radiation visible to the human eye; travels at ~300,000 km/s in vacuum.

The bouncing of light or sound off a surface.

The bending of light as it passes from one medium to another.

The number of complete wave cycles per second, measured in Hertz (Hz).

Distance traveled per unit of time; does not include direction.

The product of mass and velocity (p = mv); a measure of how hard it is to stop a moving object.

The tendency of an object to resist changes in its state of motion. Related to Newton's first law.

Thermal energy transferred from a hotter object to a cooler one.

An atom or molecule that has gained or lost electrons, giving it an electric charge.

Atoms of the same element with different numbers of neutrons.

A scale from 0–14 measuring acidity or alkalinity; 7 is neutral, below 7 is acidic, above 7 is basic.

When two dissolved substances react to form an insoluble solid.

A large molecule made of many repeating smaller units (monomers).

Large molecules made of amino acids that perform almost every function in living cells.

Movement of water through a semi-permeable membrane from an area of high water concentration to low.

Cell division that produces two identical daughter cells with the same number of chromosomes as the parent. Used for growth and repair.

Deoxyribonucleic acid; the molecule that carries genetic instructions for the development and functioning of all known living organisms.

Thread-like structures in the nucleus made of DNA and proteins that carry genetic information.

A protein that acts as a biological catalyst, speeding up chemical reactions in living cells without being consumed.

A specialised cell that transmits electrical signals in the nervous system.

A chemical messenger produced by glands that regulates body functions.

Organic compounds essential in small amounts for normal body function that the body cannot produce sufficiently on its own.

The breakdown of rocks and minerals at or near Earth's surface by physical, chemical, or biological processes.

The continuous process by which rocks are formed, changed, and recycled through igneous, sedimentary, and metamorphic stages.

A naturally occurring inorganic solid with a definite chemical composition and crystalline structure.

Horizontal lines circling the Earth parallel to the equator, measuring distance north or south of the equator in degrees.

Vertical lines running from pole to pole on Earth, measuring distance east or west of the Prime Meridian.

A celestial body orbiting the Sun, large enough to be spherical, and has cleared the neighbourhood around its orbit.

A natural satellite orbiting a planet.

A large cloud of gas and dust in space where new stars are born.

A massive stellar explosion that occurs when a large star exhausts its fuel, briefly outshining entire galaxies.

A rocky body smaller than a planet orbiting the Sun, mostly found in the asteroid belt between Mars and Jupiter.

An instrument that collects and focuses light or other radiation to observe distant objects.

The natural environment where a species normally lives and finds the resources it needs to survive.

The process by which green plants use sunlight, water, and CO₂ to produce glucose and oxygen. 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂.

The continuous movement of water through evaporation, condensation, precipitation, and runoff.

Energy from sources that are naturally replenished — solar, wind, hydro, geothermal.

The trapping of heat in Earth's atmosphere by gases like CO₂ and methane, keeping the planet warm enough for life. An enhanced greenhouse effect causes climate change.

A muscular organ that pumps blood throughout the body via the circulatory system; beats approximately 100,000 times per day.

A pair of organs in the chest that bring oxygen into the blood and remove carbon dioxide.

The organ in the skull that controls all body functions, thought, memory, emotion, and movement.

The internal framework of 206 bones that supports the body, protects organs, and enables movement.

The body's defence network of cells, tissues, and organs that fights pathogens like bacteria and viruses.

The process of breaking down food into nutrients the body can absorb and use for energy, growth, and repair.

The fluid that circulates through the body's blood vessels, carrying oxygen, nutrients, hormones, and waste products.

The science of how food provides the body with the energy and materials it needs — carbohydrates, proteins, fats, vitamins, minerals, and water.

The flow of electric charge (usually electrons) through a conductor. Measured in Amperes (A).

The electric potential difference between two points; the 'pressure' that pushes current through a circuit. Measured in Volts (V).

The opposition to the flow of electric current in a material. Measured in Ohms (Ω). Ohm's Law: V = IR.

A closed path through which electric current can flow, consisting of a source, conductors, and components.

An object that produces a magnetic field and attracts ferromagnetic materials like iron and nickel.

The generation of an electric current when a conductor moves through a magnetic field. The principle behind all electric generators.

A material that allows electric current to flow easily.

A material that strongly resists the flow of electric current.