A

Acceleration The measure of how quickly velocity (speed) increases or decreases.

Alloy A mixture of two or more elements, of which at least one is a metal.

Aluminium A light, soft metal that does not rust. It is the commonest metal found in the Earth’s rocky crust.

Atom A basic building block of matter. Atoms are not solid but are mostly made up of empty space. At the centre of the atom, subatomic particles called protons and neutrons are clumped together to form the tiny nucleus. Surrounding this are smaller electrons, which move at high speed around the nucleus.

B

Battery A device that changes chemical energy into electrical energy. When a battery is connected to a circuit, a chemical reaction inside it creates an electric current that flows out of one end of the battery, around the circuit, and back to the other end.

Bond A link between atoms.

Bronze A strong, shiny, brown alloy of tin and copper. Bronze was the first alloy to be used by humans. It was used to make weapons, tools and ornaments.

C

Carbon One of the most common elements in the Universe and the main element in all living things.

Celsius scale One of the scales used to measure temperature. Zero degrees Celsius (0°C) is the temperature of freezing water and 100°C is the temperature of boiling water, when the air pressure is normal.

Centrifugal force The force that pushes outwards on an object moving in a circle.

Centripetal force The force that pulls inwards on an object moving in a circle. Gravity (which keeps the Earth circling the Sun) or the tension in a string when your whirl it round with a weight fixed to the end, are both examples of the centripetal force at work.

Chemical energy The energy that keeps atoms bonded to one another. We make use of chemical energy in fuels. As the fuel burns, the bonds between atoms are broken, which releases energy.

Chemical reactions A chemical reaction takes place when one substance joins with another to form a completely new substance.

Chemical symbol A letter that is used to represent a chemical element. For example, C represents carbon and Cu stands for copper.

Chemistry Chemistry is the study of the composition, structure and properties of matter and the reactions between substances.

Combustion A chemical reaction in which oxygen combines with a fuel, releasing energy. This is also known as burning.

Compound A substance formed by more than one element. For example, water is a compound made up of the elements hydrogen and oxygen.

Concave lens A shaped piece of glass or plastic that is thicker at its edges than at its centre. It makes light rays diverge (spread out). When you look through a concave lens, objects appear smaller than they really are.

Concentration A measure of how strong a solution is.

Condensation The process of a gas changing into a liquid. It occurs when a gas cools down.

Conduction One of the ways in which heat energy moves. In conduction, heat passes between two objects that are touching one another.

Convection One of the ways in which heat moves. Convection only occurs in fluids (liquids and gases). When some of the molecules in a fluid are heated, they gain energy and spread away from each other. The hot part of the fluid becomes less dense than its cooler surroundings and rises upwards. But as it rises, it moves away from the source of the heat, so cools down and sinks.

Convex lens A shaped piece of glass or plastic that is thicker at its centre than at its edges. It brings light rays together at a single point called a focus. When you look through a convex lens, objects appear larger than they really are.

Copper A shiny, pinkish-brown metal. Copper is a good conductor of electricity and is often used to make wires and pipes.

Crystal A solid substance with a geometric shape. A crystal’s atoms are arranged into a pattern. Crystals have sharp edges and flat sides at regular angles to each other.

D

Density A measure of how much a particular volume of something weighs. An object is denser than another if its atoms are more tightly packed together, or if they are heavier, or both.

Drag A force that slows an object down as it travels through a gas or liquid. Drag occurs partly because of friction between the object and the molecules around it, and partly because the object uses up energy to push the molecules out of its way. Drag that takes place in the air is called air resistance.

E

Echo The sound we hear when sound waves we have already heard bounce off a surface and come back to us so we hear them again.

Electrical circuit A pathway along which an electric current can flow, for example, a battery, a light bulb and the two wires joining them together.

Electricity A form of energy made by the movement of electrons, the negatively charged particles found inside atoms. Electricity can flow when electrons are free to move through a material.

Electromagnetic radiation A form of energy that travels in waves at the speed of light. Unlike other forms of energy, such as sound waves, radiant energy can travel through empty space (a vacuum). Radio waves, microwaves, light, ultraviolet and X-rays are all forms of electromagnetic radiation. They all travel at the speed of light (in a vacuum), but they have different wavelengths—the distance between one wave crest and the next.

Electron A particle that circles around the nucleus of an atom. Electrons have a negative electrical charge, while protons carry a positive charge. Positive and negative charges attract each other, so the atom is held together.

Element An element is a substance made up of atoms of the same type. It cannot be broken down into simpler substances. Different elements have different characteristics, which arise out of the number of particles they have. There are 94 natural elements known. If atoms of one element join with atoms of another element, they form a new substance. This process is called a chemical reaction. The substance created is called a compound.

Energy The ability to make things happen, cause change and carry out work. Energy is all around us, in many different forms, including heat, light, sound, chemical, kinetic and electrical energy.

Evaporation The process of a liquid changing into a gas. Evaporation occurs when a liquid heats up.

F

Fahrenheit scale One of the scales used to measure temperature. In the Fahrenheit scale, 32 degrees Fahrenheit (32°F) is the temperature of freezing water and 212°F is the temperature of boiling water at normal air pressure.

Fluid A substance that has no fixed shape but changes shape to fill its container. Liquids and gases are both fluids.

Focus The point where rays of light meet when directed by a lens or mirror.

Force Something that changes the movement or shape of an object. Once an object is set in motion, it will carry on moving at the same speed and in the same direction until another force speeds it up, changes its direction or slows it down.

Fossil fuel A fuel formed from the remains of living things that died millions of years ago. Coal, oil and natural gas are all types of fossil fuel.

Frequency The number of vibrations, or waves, passing a certain point per second. Sound waves with high frequencies make high-pitched sounds. Sound waves with low frequencies make low-pitched sounds.

Friction A force that tries to stop things moving. Friction is produced when two surfaces rub together, or when a surface moves through a liquid or gas.

G

Gas A state of matter in which molecules are separate from each other and can move about freely. This is why gases have no fixed shape or size and can expand or contract depending on the size of their container.

Geothermal energy Energy that comes from heat stored deep inside the Earth. This energy will last for millions of years.

Gold A soft, shiny, yellow element. Gold is often found in small lumps, called nuggets. It is valuable because it is rare and does not easily spoil or rust.

Gravity The force that attracts all objects to each other. The larger an object’s mass, the greater its gravitational pull. The greater the distance between objects, the smaller the force of gravity between them.

H

Heat A type of energy that objects possess when their atoms are moving or vibrating. It is sometimes called thermal energy. The more the atoms move, the more heat the object has.

Helium One of the noble gases. Helium is one of the lightest of all gases. It is used to fill party balloons.

Hydroelectric energy Energy that comes from the kinetic and potential energy of moving water. Hydroelectric power stations control the rush of water through a dam. The movement of the water is used to generate electricity.

Hydrogen The commonest element in the Universe. It is the simplest and lightest chemical element because each atom contains one proton and one electron but no neutrons.

I

Inertia The tendency for objects to resist changes to their motion; that is, the tendency for objects that are moving to carry on moving, and for objects that are still to stay still.

Infrared (IR) radiation A form of electromagnetic radiation, with a wavelength just longer than that of visible red light. It is the radiation that you feel as heat from hot objects.

Ion An atom that is either positively or negatively charged is known as an ion. An atom that loses electrons becomes a positively charged ion, while an atom that gains electrons becomes a negatively charged ion.

Iron A heavy, silvery metal. Iron is a popular construction metal because it is abundant and strong. It is used to make steel and can be used as a magnet. Iron is also a vital element needed by the human body: iron inside our red blood cells helps to carry oxygen around our bodies.

K

Kinetic energy The energy that an object has because of its movement. For example, a ball rolling down a hill has kinetic energy. The faster it rolls, the more kinetic energy it has.

L

Lead A dense, bluish metal that turns grey when exposed to the air and has a very low melting point.

Lever A stiff bar that pivots at a fulcrum.

Lift An upward force that holds aircraft in the air. As an aeroplane moves, the shape of its wings forces air to flow faster over the top of the wing than the air flowing beneath it. This means that there is less pressure on the upper side of the wing than on the lower side. The result is lift.

Light A kind of energy that our eyes can detect, enabling us to see. A kind of electromagnetic radiation, light is mostly produced by very hot things. It travels in straight lines, but it can reflect (bounce) off objects. In fact, we can only see an object when light reflects from it and into our eyes, or if it produces light itself. Sunlight is not colourless, but is made up of all the colours of the rainbow: the spectrum of light.

Lightning A visible spark of electricity produced during a thunderstorm. Static electricity builds up inside clouds when ice and water molecules bump against each other and become electrically charged. If enough charge builds up in the cloud, it produces a flash of lightning. The light we see is a strip of air being suddenly heated by the electricity. The heat of the flash makes the air around it expand so fast it makes a loud boom of thunder.

Liquid A state of matter in which molecules are close to each other but not fixed rigidly together. The molecules can move about to fill the bottom of their container. Liquids can be easily poured.

M

Machine A device that changes the direction or size of a force, making it easier to perform certain tasks. The most simple machines are: a wheel and axle, a lever, a wedge, a screw, a pulley and an inclined plane.

Magnesium A light, silvery-white metal. Magnesium easily reacts with other elements and burns with a bright white flame. It is used to make fireworks or mixed with other metals to make alloys that are strong but light.

Magnet An object that has two ends, called poles, and produces a magnetic force field around itself. Most magnets are made of the metals iron or steel and attract other objects made of these materials. The Earth itself has a magnetic field, as if it had a magnet inside it.

Magnetism The invisible force of attraction or repulsion between magnetic materials. Electricity can produce magnetism and magnetism can produce electricity.

Mass The amount of matter in an object.

Matter Every thing around us, living creatures, lumps of rock, or even invisible gases, is made up of matter. Matter exists in three main forms, or states. These are: solid, liquid and gas. All matter is made up of tiny building blocks called atoms.

Melting The process of a solid changing into a liquid. Melting occurs when a solid heats up and reaches its melting point.

Mercury A silvery liquid metal. Mercury is the only metal that is a liquid at room temperature. It is used inside some thermometers.

Metals Metals are the largest group of chemical elements. Metals conduct heat and electricity well compared to non-metals. Most are solid at room temperature. They are strong, hard and tough, and can be polished to give a smooth, shiny surface. When they are squeezed under great pressure, they change shape and become squashed, rather than splintering apart or shattering.

Microwaves A form of electromagnetic radiation with a wavelength longer than infrared radiation. Microwaves are used in communications. Some microwave frequencies can also be used in cooking.

Mirror A sheet of glass with a thin layer of metal on the back. Mirrors form images by reflecting light from the surface of the metal.

Mixture A blend of two different substances that are not chemically changed by being put together. Sand and salt combined produce a mixture—neither the salt nor the sand are chemically changed.

Molecule The smallest part of a substance that can exist by itself and still possess its chemical properties. A molecule consists of atoms, either of the same type, or a combination of different types of atom bonded together.

Momentum The tendency for objects that are moving to carry on moving.

Motion The word given to any kind of movement. All movement is caused by forces. An object going in a straight line has linear motion. An object that circles a central point has circular motion.

N

Neutron A subatomic particle found in the nucleus of an atom. Neutrons have no electrical charge.

Newton, Isaac (1642–1727) The English scientist who discovered the laws of gravity and motion. Isaac Newton proposed that the Earth’s gravity attracted the Moon and kept it circling the Earth.

Nickel A silvery-white metal. It is used to make stainless steel and other alloys.

Nitrogen A colourless, odourless gas that makes up 78% of the air around us.

Nuclear energy The energy contained by an atom, due to the strong force that holds together the protons and neutrons in its nucleus. There are two ways of releasing nuclear energy. These are: nuclear fission and nuclear fusion. They are both forms of nuclear reaction.

O

Opaque A word used to describe a material that does not allow light to shine through it.

Ore Rock that contains metals or other useful materials.

Oxidation A reaction in which oxygen combines with another chemical.

Oxygen A colourless, odourless gas that makes up one-fifth of the air around us. Oxygen is crucial to much life on Earth as humans and other animals must breathe oxygen to stay alive.

P

Pitch How high or low a sound is. High-pitched sounds have high frequencies and low-pitched sounds have low frequencies.

Plastic A type of man-made, or synthetic, material that is made in laboratories or factories. It is made of long molecules. Plastics are useful materials because they are easy to shape and are often light and long-lasting. Most plastics are made from compounds of hydrogen and carbon.

Potential energy Energy that is stored. For example, a boulder on a hillside has potential energy. As the boulder starts to roll under the force of gravity, its potential energy gradually changes into kinetic energy.

Pressure The amount of force acting on a certain area.

Primary colours Any of the three colours that can be mixed together to form all other colours. The primary colours of light are red, green and blue. They can be mixed to make any colour. When all three are mixed together they make white light.

Prism An angled block of transparent material such as clear glass or plastic. As light waves pass through a prism, their different colours spread out to form a spectrum, which looks like a rainbow.

Proton A subatomic particle found in the nucleus of an atom. Protons have a positive electrical charge.

R

Radar (Radio Detection And Ranging) A system that detects objects by transmitting radio waves and receiving the echoed signals that bounce back from them. Radar has many uses. Ships and aeroplanes have radar systems in order to detect other craft or oncoming storms. 

Radiation One of the ways in which heat moves. Radiant heat travels in the form of waves. Unlike conduction and convection, radiation can travel through empty space (a vacuum). This is how the Sun’s heat reaches the Earth.

Radio waves A form of electromagnetic radiation with a very long wavelength. Radio waves are used in communications and broadcasting.

Rainbow An arch of colours that forms across the sky when the Sun shines from behind you at rain falling in front of you. The raindrops act as millions of tiny prisms, each splitting the white light in sunlight into every colour of the spectrum.

Reflection The bouncing of light rays off an object. Smooth, shiny, light surfaces reflect more light than rough, dark ones.

Refraction The bending of light rays as they travel through different transparent materials. This occurs because light travels at different speeds through different materials. At the boundary between two materials, the light changes speed and is bent from its straight path.

Renewable energy Energy sources that will not run out because they are constantly replenished. Renewable energy comes from natural sources, such as sunlight, waves, tides, wind and geothermal heat.

S

Shadow A dark shape or area produced when an opaque object stands between a surface and a source of light. Shadows are formed because light can only travel in straight lines and cannot bend around the opaque object.

Silver A soft, bright, shiny metal. Silver is a precious metal, used to make ornaments and jewellery.

Solid A state of matter in which molecules are tightly locked together in a rigid pattern. This gives solids a fixed shape.

Soluble The ability of one substance to dissolve in another one.

Solution A liquid mixture of two different substances. One substance, usually a solid, is dissolved in another substance, known as the solvent, which is usually a liquid. For example, table salt stirred into water makes a solution (called saline).

Sonar (Sound Navigation And Ranging) A technique that uses sound waves to detect solid objects. The sound waves bounce off them and reveal their position. Ships use sonar to find shoals of fish or other ships.

Sound A form of energy made when objects vibrate (move to and fro rapidly). As an object vibrates it sets the air, liquid or ground around it vibrating too: molecules press close together and then pull apart. These sequences of higher and lower pressure are called sound waves.

Static electricity Electricity that does not move. Static electricity is produced when two objects rub against each other and electrons rub off from one material on to the other. The material that has lost electrons becomes positively charged; the material that has gained them becomes negatively charged.

Steel An alloy of iron, carbon and, usually, other elements. There are many different types of steel alloys, each containing slightly different amounts of various elements, and each designed to do a different task.

Subatomic particles The tiny parts that make up an atom. They include electrons, neutrons and protons.

Sulphur An element that is found in some rocks. It readily forms bonds with other elements. It is used in gunpowder and matches because it easily catches alight.

T

Temperature A measure of how hot or cold something is. Adding heat energy to an object increases its temperature.

Thermometer An instrument used to measure temperature. Glass thermometers are made of a long glass tube containing alcohol or mercury, which expands as it heats, and rises up the tube.

Tin A silvery metal that can easily be bent and shaped. Tin was once used to make cans and foil, but aluminium has since taken its place, because it is cheaper.

U

Ultrasound Sounds that are too high-pitched for humans to hear. Some animals, such as dogs and bats, can hear some of them. An ultrasound scanner is used to make images of the inside of the human body.

Ultraviolet (UV) radiation A form of electromagnetic radiation with a wavelength just shorter than that of visible violet light. Some of the energy emitted by the Sun takes the form of UV radiation.

V

Vacuum A place where there is a complete absence of matter.

Velocity A measure of both how quickly an object moves and the direction in which it travels.

Viscosity A measure of how thick a liquid is. For example, honey is thicker and more viscous than water.

Volume The amount of space taken up by an object.

W

Wavelength The distance between one wave and the next. Sound waves with short wavelengths have high frequencies and make high-pitched sounds. Sound waves with long wavelengths have low frequencies and make low-pitched sounds.

Weight A measure of the gravitational force pulling on an object. A big book is weighty because it is pulled downwards by the Earth’s gravity. In space, away from the Earth’s gravity, objects and people are become weightless and move about freely. Objects in space still have mass, however.

X

X-rays A form of electromagnetic radiation with very short wavelengths and extremely high frequencies. They pass right through some solids. In medicine they can be used to see the structure of bones and internal organs.

Z

Zinc A bluish-white metal. It is used as a rust-proof coating.

Consultant: Mike Goldsmith