RBSE Praveshika Science key terms

Anything that has mass and occupies space. Matter is made of tiny particles that are always moving, have gaps between them and attract one another; it exists mainly as solid, liquid or gas.

The spontaneous spreading of the particles of one substance through another because of their random motion, from a region of higher concentration to a region of lower concentration. It is fastest in gases and at high temperature.

The change of a liquid into vapour at any temperature below its boiling point, happening only at the surface. It causes cooling, because the fast-moving particles that escape carry heat energy away with them.

The heat energy needed to change one kilogram of a liquid at its boiling point into vapour at the same temperature, with no rise in temperature. For water it is about 2260 kJ per kg.

The tendency of a body to resist any change in its state of rest or of uniform motion in a straight line. It depends on the mass of the body, so a heavier object has greater inertia.

The rate at which the velocity of a body changes with time. It is a vector quantity measured in metres per second squared; it is positive when speed increases and negative (retardation) when speed falls.

The force of attraction between any two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

The motion of a body under the influence of gravity alone, with no air resistance or other force acting on it. Near the Earth's surface all freely falling bodies accelerate downwards at about 9.8 m/s².

Work is done when a force moves an object along its own direction. It equals force multiplied by displacement, is measured in joules, and is zero when the displacement is perpendicular to the force.

The energy a body possesses because of its motion. It equals half the mass multiplied by the square of the speed, so doubling the speed makes the kinetic energy four times greater.

Energy can neither be created nor destroyed; it can only be changed from one form into another. The total energy of an isolated system stays constant, though some may become low-grade heat.

The rate at which work is done or energy is transferred. Power equals work divided by time and is measured in watts, where one watt equals one joule per second.

A sound heard again after it is reflected from a distant hard surface such as a wall or cliff. To be heard separately, the reflected sound must reach the listener at least 0.1 second after the original.

The bouncing back of light when it strikes a surface. The angle of incidence equals the angle of reflection, and the incident ray, the reflected ray and the normal all lie in one plane.

The ratio of the speed of light in vacuum to its speed in a given medium. It shows how strongly a medium bends light; a larger value means light travels slower and bends more.

The distance between the pole (or optical centre) of a mirror or lens and its principal focus. It tells how strongly the mirror or lens converges or diverges a beam of light.

Short-sightedness: a defect in which a person sees nearby objects clearly but distant objects blurred, because the image is formed in front of the retina. It is corrected using a concave lens.

At constant temperature, the current flowing through a metallic conductor is directly proportional to the potential difference across its ends; that is, V = IR, where R is the resistance.

The property of a conductor that opposes the flow of electric current through it. It is measured in ohms and increases with length and temperature, but decreases when the wire is made thicker.

The rate at which an electrical device consumes or delivers energy. It equals voltage multiplied by current (P = VI) and is measured in watts; the kilowatt-hour is the commercial unit of electrical energy.

The production of a current in a coil when the magnetic field linked with it changes, for example when a magnet is pushed towards it. This is the principle of the electric generator.

An equation in which the number of atoms of each element is the same on both sides, so that mass is conserved. Coefficients are written before formulas to balance it, while subscripts inside formulas are never changed.

A reaction in which a substance gains oxygen, or loses hydrogen or electrons. Burning of fuels, rusting of iron and the browning of cut fruit are everyday examples of oxidation.

A reaction in which one compound breaks down into two or more simpler substances. It usually needs heat, electricity or light, as when calcium carbonate is heated to give quicklime and carbon dioxide.

A number scale from 0 to 14 that measures how acidic or basic a solution is. Values below 7 are acidic, 7 is neutral and values above 7 are basic; each step means a tenfold change in hydrogen ion concentration.

The reaction of an acid with a base to form a salt and water. The acidic and basic properties cancel each other; for example, hydrochloric acid with sodium hydroxide gives sodium chloride and water.

A substance that changes colour to show whether a solution is acidic or basic. Litmus turns red in acid and blue in base, and natural indicators such as turmeric paste or red cabbage juice also work.

A homogeneous mixture of a metal with one or more other elements, made to improve properties such as hardness, strength or resistance to corrosion. Steel, brass and solder are common examples.

The existence of an element in two or more different forms in the same physical state, differing in the arrangement of their atoms. Diamond, graphite and fullerene are allotropes of carbon with very different properties.

An atom or group of atoms that gives a family of organic compounds its characteristic chemical properties. Examples are the hydroxyl group in alcohols and the carboxyl group in carboxylic acids.

The process by which green plants use sunlight, carbon dioxide and water to make glucose and oxygen in the chloroplasts. Chlorophyll absorbs the light, and the food made supports the plant and indirectly animals.

A quick, involuntary response to a stimulus in which a message travels along a reflex arc from a receptor through the spinal cord to a muscle, without waiting for the brain to decide.

A chemical messenger made in small amounts by an endocrine gland and carried by the blood to a target organ, where it controls processes such as growth, blood sugar level or the menstrual cycle.

A method of asexual reproduction in which a single-celled organism divides into two identical daughter cells, as in Amoeba and bacteria. The offspring produced are genetically alike.

The characteristic that appears in an offspring when two contrasting inherited factors are present together. In pea plants the tall form is dominant and masks the short, recessive form.

The process by which individuals with variations better suited to their surroundings survive and reproduce more successfully, so those helpful traits become more common in later generations.

The sequence through which energy and nutrients pass from one organism to another by eating, starting with a producer and ending with a top consumer. Each step in it is a trophic level.

The thinning of the ozone layer in the upper atmosphere, mainly caused by chlorofluorocarbons and other halogen-containing compounds. Less ozone allows more harmful ultraviolet radiation to reach the Earth's surface.

Materials or energy obtained from nature that living things use, such as air, water, soil, forests and minerals. Renewable resources can be replaced, while non-renewable ones such as coal are used up.