ILLUSTRATED

ENCYCLOPEDIA

SCIE

NCE

ISBN 978 1 7418 3760 1

9 781901 323511

The colour wheel shows howthe different colours of lightadd up to make white light. Whenyou spin the wheel, the colours whirlaround so fast that the eye cannotfollow them. Inside the eye each colourmerges with the others so the eye sees allthe colours at once—and all colours oflight added together make white light.

Female glow-worms(a type of beetle)emit light when theyare ready to mate.

A rainbow shows allthe different colours

of the spectrum.

Spectrum of light The section of theelectromagnetic spectrum ( 28) that wecan see. It is formed of all the differentcolours that make up white light:red, orange, yellow, green, blue, indigoand violet.

When the three primary colours of light, red, blueand green are added together they make white light.

Speed of light The speed at which lighttravels through empty space. This is about300,000 km/s—about seven and a halftimes around the Earth in one second. Thespeed of light is the speed limit for theUniverse: nothing can travel faster.

Translucent A material that allows light topass through it, but which spreads thelight rays out in all directions. We canmake out shapes behind translucentmaterials but we cannot see them clearly.Tracing paper and ice are bothtranslucent materials.

Convex lens A shaped piece of glass orplastic that is thicker at its centre than atits edges. It brings light rays together at asingle point called a focus. When you lookthrough a convex lens, objects appearlarger than they really are.

Diffraction The spreading out of light raysas they pass through a narrow gap.

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

Lens A shaped piece of glass or plasticthat bends light rays.

Light filter A piece of coloured,transparent plastic or glass that allowslight of its own colour to pass through it,but stops all other colours. Light filters areoften used in stage lighting, to change thecolour of a light. If a blue filter is placedover a white light, the light that shines onto the stage will be blue.

Luminescence Light that is createdat low temperatures, usuallycaused by certain chemical reactionsor electricity.

Mirage A trick of the eye, that makesfar away objects look much closer thanthey really are. Mirages happen whenlight from the sky is reflected off a layerof hot air just above the ground or thesea. They are commonly seen in deserts.

! It takes sunlight more than eightminutes to travel nearly 150 million km fromthe Sun to the Earth.

! In one year, light travels 9.46 trillion km.This distance is called a light year.

! The colour of an object depends onwhich colours it absorbs and which itreflects. For example, a leaf looks greenbecause its surface absorbs all the colours inwhite light, except green, which it reflects.

! The eye contains a natural convex lenswhich focuses an image on to the retina atthe back of the eye.

! Concave lenses are used in glasses forpeople who are short-sighted (they havedifficulty seeing objects far away fromthem). Convex lenses are used for peoplewho are long-sighted (they have difficultyseeing objects close to them).

Light is a kind of energy ( 18) that oureyes can detect, enabling us to see. Itis mostly produced by very hotthings. It travels in straight lines, but it canreflect (bounce) off objects. In fact, wecan only see an object when light reflectsfrom it and into our eyes, or if it produceslight itself. Sunlight is not colourless, but ismade up of all the colours of the rainbow:the spectrum of light.

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Prism An angled block of transparentmaterial such as clear glass or plastic. Aslight waves pass through a prism, theychange speed and are bent, or refracted.Longer waves of red light refract least.Shorter waves of violet light refract most.The other colours of the spectrum spreadout in between.

Rainbow An arch of colours that formsacross the sky when the Sun shines frombehind you at rain falling in front of you.The raindrops act as millions of tinyprisms, each splitting the white light in sunlight into every colour of the spectrum.

Reflection The bouncing of light rays offan object. Smooth, shiny, light surfacesreflect more light than rough, dark ones.

Refraction The bending of light rays asthey travel through different transparentmaterials. This occurs because light travelsat different speeds through differentmaterials. At the boundary between twomaterials, the light changes speed and isbent from its straight path.

Shadow A dark shape or area producedwhen an opaque object stands between asurface and a source of light. Shadows areformed because light can only travel instraight lines and cannot bend around theopaque object.

Mirror A sheet of glass with a thin layer of metal on the back. Mirrors formimages by reflecting light from the surfaceof the metal.

Opaque A material that does not allowlight to shine through it.

Pigment A substance that is added toanother substance to give it colour.

Primary colours Any of the threecolours that can be mixed together

to form all other colours. The primarycolours of light are red, green and blue.They can be mixed to make any colour.When all three are mixed together theymake white light. In paints, which containpigments, the primary colours are red,yellow and blue.

A prism refracts whitelight, splitting it into everydifferent colour of thespectrum.

Light is producedin a bulb when thefilament is heatedby an electricalcurrent.

Bioluminescence The ability of someanimals to produce light. The light isgenerated by chemical reactions ( 14) inthe animal’s body.

Concave lens A shaped piece of glass orplastic that is thicker at its edges than atits centre. It makes light rays diverge(spread out). When you look through aconcave lens, objects appear smaller thanthey really are.

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Filament

Transparent A material that transmitslight, or allows light to pass through it. Wecan easily see through transparentmaterials, such as glass. We can see theglass because a tiny amount of light isreflected off the material.

By placing two mirrors in a tube you can make aperiscope, a device used to see around corners.Light coming in at one end is reflected through tothe viewer at the other end.

A magnifying glass isa convex lens.

A concave lens (top) and convex lens (bottom).

! Covers 12 major subject areas of science

! More than 200 keywords alphabetically listedand clearly explained

! Fact panels with extra information

! More than 70 detailed illustrations

! Comprehensive index

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First published in 2012 by Orpheus Books Ltd., 6 Church Green, Witney, Oxfordshire, OX28 4AW, England

www.orpheusbooks.com

Copyright ©2012 Orpheus Books Ltd.

Created and produced by Nicholas Harris, Sarah Hartley, Katie Sexton, Ruth Symons and Erica Williams, Orpheus Books Ltd.

Text Ruth Symons

Illustrated by Susanna Addario, Chris Chapman, Elisabetta Ferrero, Guiliano Fornari, Mike Fuller, Andrea Ricciardi di Gaudesi, Gary Hincks,

Stewart Lees,Shane Marsh, Lee Montgomery, Steve Noon, Sebastian Quigley, Alessandro Rabatti, Eric Robson, Claudia Saraceni, Roger Stewart,

Thomas Trojer, Mark Wilkinson, Martin Woodward and David Wright

Consultant David Hawksett, astronomer, writer and broadcaster

All rights reserved. No part of this book may be reproduced, stored in aretrieval system, or transmitted in any form or by any means, electronic,

mechanical, photocopying, recording or otherwise, without the prior writtenpermission of the copyright owner.

ISBN 978 1 7418 3760 1

Printed and bound in Singapore

Photographs on pages 9, 25, 27 and 29: Science Photo LibraryPhotograph on page 11: Wikimedia Commons/Public Domain

Photograph of scientist on page 14: Copyright ©2010 Alexander Raths Used under licence from Shutterstock.com

Photograph of windmill on page 19: Copyright ©2010 T.W. van UrkUsed under licence from Shutterstock.com

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TTHHEE PPEERRIIOODDIICC TTAABBLLEE 1100

MMEETTAALLSS 1122

CCHHEEMMIICCAALL RREEAACCTTIIOONNSS 1144

FFOORRCCEESS && MMOOTTIIOONN 1166

EENNEERRGGYY 1188

SSOOUUNNDD 2200

CCOONNTTEENNTTSS AABBOOUUTT TTHHIISS BBOOOOKK

Each double page contains a briefintroduction, explaining the general subject,followed by key words arranged in alphabeticalorder. To look up a specific word, turn to the indexat the back of this book: this will tell you which pageto go to. If you want to learn more about a subject, takea look at the factfile, or follow the arrows to read related entries.

SSOOUUNNDDEcho The sound we hear when soundwaves bounce off a surface.

Echolocation A type of sonar used byanimals such as bats and whales. Theanimals emit sounds and listen to theirechoes in order to locate solid objects.Echolocation alows animals to hunt indark or murky conditions where it isdifficult to see.

Musical instrument An object that is usedto make musical sounds. In a cello, a bowrubs over the cello’s strings to make themvibrate. The vibrations pass into the airand also to the cello’s hollow body,making the sound louder and richer.

Noise Any kind of sound. Noise is oftenused as a word for unwanted sounds.

Pitch How high or low a note is. High-pitched sounds have high frequencies andlow-pitched sounds have low frequencies.

Resonance The frequency at which anobject will vibrate if you hit it. This issometimes called the natural frequencyof an object.

Reverberation The sound heard whensound waves continue to travel after theoriginal source of a sound has gone.

Sonar (SOund Navigation And Ranging)A technique that uses sound waves todetect solid objects. The sound wavesbounce off them and reveal their position.Ships use sonar to find shoals of fish orother ships.

Speed of sound The speed at which soundtravels. Sound travels through air at about343 metres per second. The speed ofsound varies depending on the substanceit travels through. Loud and soft soundsall travel at the same speed.

Volume The loudness of a sound. Volumeis measured in decibels (dB). Some soundsare so quiet that we can only just hearthem. Others are so loud that they maydamage our ears. (See intensity.)

Wavelength The distance between onesound wave and the next. Sound waveswith short wavelengths have highfrequencies and make high-pitchedsounds. Sound waves with longwavelengths have low frequencies andmake low-pitched sounds.

! Whales and dolphins use sound tocommunicate. Whalesong can travel up to800 km under water. Whales are believedto be the loudest animal in the world. They can make sounds as loud as 188 dB.The loudest land animal is the howlermonkey. Its calls can be as loud as 88 dB and can be heardup to 16 km away.

! Sound wavescan only travelthrough matter.Space iscompletely silentbecause there areno gas moleculesfor sounds to passalong.

! Most sounds onlycarry a relatively smallamount of energy. Thesound of 200 pianosplaying togetherproduces about thesame amount of energyas it would take to lightone light bulb.

Sound is a form of energy ( 18) madewhen objects vibrate (move to and frorapidly). As an object vibrates it sets theair around it vibrating too: molecules ofthe gases in the air press close togetherand then pull apart. These regions ofhigher and lower air pressure are calledsound waves. They move away from thesound source in all directions, like ripplesin a pond. Sounds also travel as vibrationsthrough liquids and solids. The moleculesare closer together in liquids and solidsthan in gases, so sounds travel throughthem much faster.

Infrasonic Sounds that are too low-pitchedfor humans to hear. It is thought that someanimals are able to hear them.

Intensity The amount of energy that soundwaves carry. The intensity of sound wavesdetermines their volume.

Music A form or art using pleasant sounds.

Acoustics The study of how sound isaffected by location, for example, howsound bounces around a concert hall.

Amplitude The height of a wave. Soundwaves with high amplitudes make loudsounds and sound waves with lowamplitudes make quiet sounds.

Decibel The unit used to measure thevolume, or intensity, of sounds. A veryquiet sound, such as the rustling of leavesis about 20 decibels (dB). A very loudsound, such as a rocket taking off, is about120 dB. Sounds over 80 dB can damageyour ears.

Frequency The number of vibrations, orsound waves, per second. Sound waveswith high frequencies make high-pitchedsounds. Sound waves with lowfrequencies make low-pitched sounds.

Hertz The unit used to measurefrequency. One hertz(Hz) is one vibrationper second.

Stringedinstruments

Sound travels quickest through solids, slowerthrough liquids and slowest of all through air.

The Bell X-1 rocket plane was the firstaircraft to fly faster than the speed of sound.

Sound waves traveloutwards from their sourcelike ripples on a pond.

A trumpet producessound waves.

Supersonic Faster than the speed ofsound. When objects travel faster thanthe speed of sound the they make a loudnoise called a sonic boom.

Ultrasound Sounds that are too high-pitched for humans to hear. Someanimals, such as dogs and bats, can hearthem. An ultrasound scanner is used tomake images of inside the human body. Itbeams high-pitched sound waves into thebody. A computer transforms the echoesinto an image.

Water (1530 mper second)

Air (343 mper second)

Steel (5050 mper second)

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An ultrasound scan of a baby in the womb

A watch makes a soft,medium-pitched sound.

Bats useecholocation totrack their prey.

A rocket makes a loud,low-pitched sound.

A singer makesa medium-loud,medium-pitchedsound.

The sound made by a jet enginemeasures about 140 dB, but it canonly be heard faintly from thestreet because it is so far away.

An electric drill isabout 100 dB. The

people that use it must wear ear-protectors.

Busy traffic can registerbetween 70 and 80 dB.

The sound of a carhorn can be up to110 dB.

ARROWS These arrows show you where to look up otherwords mentioned in the entry. For example, ( 26) tells you to go forward to page 26 and ( 6) tells you to turn back to page 6.

INTRODUCTIONThis explains thegeneral subjectand provides somebasic knowledge.

KEY WORDS AND ENTRIESKey words are arranged alphabeticallyacross each double page. Each entryprovides a short explanation of whatthe key word means.

FACTFILEThe factfile provides extrainformation on the subject. Factsare presented in easy-to-readbullet points.

PAGE NUMBERPage numbersare easy to findat the side ofthe page.

BOLD WORDSThese highlightuseful words thatdo not have theirown entry.

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HHEEAATT 2244

EELLEECCTTRRIICCIITTYY&& MMAAGGNNEETTIISSMM 2266

EELLEECCTTRROOMMAAGGNNEETTIICCSSPPEECCTTRRUUMM 2288

IINNDDEEXX 3300

The air inside a hot airballoon is less dense thanthe cooler air outside,making it buoyant.

Inside an atom. Protons and neutrons aregathered in the atom’s nucleus.

Electrons circle the nucleus.MMAATTTTEERR

Atom A basic building block of matter.Atoms are not solid but are mostly madeup of empty space. At the centre of theatom, the subatomic particles protonsand neutrons are clumped together toform the nucleus. Surrounding this aresmaller electrons, which move at speedaround the nucleus.

Atomic number The number of protonsfound in the nucleus of an atom.

Condensing The process of a gaschanging into a liquid. Condensationoccurs when a gas cools down or issubject to an increase in pressure ( 17).

Plasma A state of matter rare on Earth,found at very high temperatures. Forexample, plasma is found inside moststars, including our local star, the Sun. Agas becomes a plasma when it is so hotthat its atoms collide with each other. Theforce of the collisions knocks electronsloose from some atoms, so that the gasbecomes electrically charged ( 26).

Properties of matter The characteristicsof a substance. Chemical properties relateto the structure of atoms in a substance.Physical properties are characteristicsthat can be easily observed, such asweight, shape, density and colour.

Proton A subatomic particlefound in the nucleus of an atom.

Protons have a positive electricalcharge ( 26).

Radioactivity Particles or rays of energygiven off by unstable atoms, for example,uranium. An unstable atom is one that is likely to give off one of its subatomicparticles.

Solid A state of matter in which moleculesare tightly packed together in a rigidpattern. This gives solids a fixed shape.

States of matter The three main forms inwhich matter exists. These are: solid, liquidand gas. A change of state is caused by achange in temperature or pressure ( 17).

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

Sublimation The process of a solid turningstraight into a gas without first becoming a liquid.

Vacuum A place where there is a completeabsence of matter.

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Geysers demonstrate how waterchanges from one state toanother. Water is heated byunderground rocks. It shoots upas steam and hot water. When itcomes into contact with the coldair it condenses and falls to theground as water.

Every thing around us, livingcreatures, lumps of rock, or eveninvisible gases, is made up ofmatter. Matter exists in three mainforms, or states. These are: solid, liquidand gas. All matter is made up of tinybuilding blocks called atoms. They are fartoo small for us to see and arethemselves made up of even tinier partscalled subatomic particles.

! A pinhead contains about one billionbillion atoms.

! The Greek philosopher Democritus (460-400 BC) was the first person to suggest thatmatter was made up of tiny particles.

! The nucleus of a hydrogen atom is100,000 times smaller than the whole atom.If the nucleus was a golf ball in the centre ofa stadium, the edge of the atom would bethe stadium’s outer wall.

! Radioactivity wasdiscovered byFrench physicistHenri Becquerelin 1896 andnamed by Polish-born scientistMarie Curie. In 1903,Becquerel, Curie andCurie’s husband Pierreall won the Nobel Prizefor Physics for their discovery.

76

Gas

LiquidSolid

Evaporation The processof a liquid changing into a gas. Evaporationoccurs when a liquidheats up or experiencesa drop in pressure ( 17).

Fluid A substance thathas no fixed shape but

changes shape to fill itscontainer. Liquids and gases

are both fluids.

Freezing The process of a liquidchanging into a solid. Freezing occurs whena liquid cools down or is subject to anincrease in pressure ( 17).

Gas A state of matter in which moleculesare separate from each other and canmove about freely. This is why gases haveno fixed shape and can expand or contractdepending on the size of their container.

Liquid A state of matter in which moleculesare close to each other but not fixed rigidlytogether. The molecules can move aboutto fill the bottom of their container. Liquidscan be easily poured.

Mass The amount of matter in an object.

Melting The process of a solid changinginto a liquid. Melting occurs when a solidheats up and reaches its “melting point”.

Molecule The smallest part of a substancethat can exist by itself and still possess itschemical properties. A molecule consists ofatoms, either of the same type, or acombination of different types of atombonded together with molecular bonds.

Neutron A subatomic particle found in thenucleus of an atom. Neutrons have noelectrical charge ( 26).

Nucleus The centre of an atom, made up ofprotons and neutrons.

Density A measure of how compactsomething is. An object is denser thananother if its atoms are more tightlypacked together.

Electron A subatomic particle that circlesthe nucleus of an atom. Electrons do notmove at random, but stay in layers knownas shells. Electrons have a negativeelectrical charge ( 26), while protonscarry a positive charge. Positive andnegative charges attract each other, sothe atom is held together.

Air-filled buoys are attached by a chain toa heavy weight on the seabed. This stopsthe buoy from floating away.

The air inside a boat makes it lessdense than water, so it floats.

Rubber rings float becausethey are full of air.

Viscosity A measure of how thick a liquidis. For example, honey is thicker and moreviscous than water.

Volume The amount of space taken up byan object.

When you try to swimdownwards, the waterpushes you back up.

Nucleus

Electron

Proton

Neutron

A glacier is a slow-moving mass of ice.It is water in itssolid state.

Marie Curie

Density determines whether things float or sink. Ifan object is denser than water it will sink. If it is lessdense, it will float.

Water is both a molecule and a compound. It ismade up of oxygen atoms and hydrogen atoms.

Hydrogen The commonest element in theUniverse. It is the simplest and lightestchemical element because each atomcontains one proton and one electron butno neutrons ( 6). Hydrogen joins withoxygen to make water. It also joins withcarbon and oxygen to makecarbohydrates, found in starchy foodssuch as potatoes and rice. Polymer A large molecule made from

chains of smaller molecules calledmonomers. Many types of plastics andother artificial materials such as acrylic andnylon are polymers. Naturalpolymers are found in ourhair and in DNA.

An element is a substance made upof atoms ( 6) of the same type. Itcannot be broken down intosimpler substances. Different elementshave different characteristics, which aredetermined by the number of subatomicparticles ( 7) they have. There are 94natural elements known to us. These aredivided into metals ( 12) and non-metals.If atoms of one element join with atomsof another element, they form a newsubstance. This process is called achemical reaction ( 14). The substancecreated is called a compound.

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Nitrogen A colourless, odourless gas thatmakes up 78% of the air around us.Nitrogen is essential for life because itmakes up a part of all living cells.

Noble gases A group of gases that havesimilar characteristics. They are sometimesknown as the inert gases because they donot easily form compounds with otherelements. One common noble gas is neon,which is used to make lights and streetsigns. Because it does not react with otherelements, it will not ignite or explode.

Oxygen A colourless, odourless gas thatmakes up one-fifth of the air around us.Oxygen is crucial to much life on Earth ashumans and other animals must breatheoxygen to stay alive.

Phosphorus A chemicalelement that is found in

many rocks andminerals. It is also

found inside our bonesand DNA. In its basic form,

phosphorus is highly flammable.

Plastic A man-made, or synthetic material,that is made in laboratories orfactories. Plastics are usefulmaterials because they are easy toshape and are often light andlong-lasting. Most plastics aremade from compounds of hydrogen andcarbon and are a type of polymer.

Oxygen atoms Hydrogen atoms Water molecules=+

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

Valency The number of bonds anatom can possibly make withother atoms.

Diamond is a very hard allotrope of carbon.

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About 90% of the planet Saturn ismade up of hydrogen.

In an ionic bond an atom loses or gains electrons.Here a sodium atom (right) has donated one electronfrom its outer shell to an atom of chlorine (left).Sodium becomes positively charged, and chlorinebecomes negatively charged. Positive and negativeattract and keep the atoms bonded together,producing a molecule of sodium chloride.

Scuba divers carry oxygen in a tank on their back sothat they can breathe underwater.

! Hundreds of years ago, scientistsbelieved that all things were made up of fourelements—earth, air, fire and water.

! The bodies of all living things are madeup of carbon-based molecules. This includesour own skin, hair, muslces, bones and brain,as well as parts of animals and plants.

! Carbon-based molecules outnumbertenfold the molecules of all the otherelements put together.

! The word “plastic” comes from the Greek word plastikos meaning “to form”. Itis called this because it is easyto form intodifferent shapes.

98

In a covalent bond (above) one atom shares anelectron with another atom. Here, two hydrogenatoms are bonded covalently to one oxygen atom.

Carbon One of the most commonelements in the Universe and the mainelement in all living things.

Chemical symbols A letter that is used torepresent a chemical element. Forexample, C represents carbon and Custands for copper.

Cohesion The force of attraction betweenatoms of the same element or compound.

Compound A substance formed by morethan one element. For example, water is acompound made up of hydrogen andoxygen atoms.

Covalent bond A bond betweenatoms, where one atomshares an electron ( 6)with another atom.

Crystal A solidsubstance with ageometric shape. A crystal’satoms are arranged into a pattern.Crystals have sharp edges and flat sides atregular angles to each other.

Halogens A group of non-metallicelements with similar characteristics. Theyeasily form bonds with other elements.The halogens are: chlorine, fluorine,bromine, iodine and astatine.

Helium One of the noble gases. Helium isthe lightest of all gases. It is used to fillparty balloons.

Ionic bond A bond between atoms, wherean electron leaves one atom and joinsanother. An atom that loses an electronbecomes positively charged, while an atomthat gains an electron becomes negativelycharged. Atoms that have becomepositively or negatively charged are knownas ions. Positive ions attract negative ions.This keeps the atoms bound together.

Metallic bond A bond between atoms in ametal. The metal’s electrons flow freelyfrom one atom to another.

Egg yolk is rich in theelement sulphur.

Bones containcalcium, carbon,phosphorus and sodium.

Table salt is a compound ofthe elements sodium andchlorine. Its scientificname is sodiumchloride.

This plastictoothbrush is mostlymade up of a compoundof hydrogen and carbon.

Adhesion The force of attraction between the atoms of two differentelements or compounds.

Allotrope Different forms of the sameelement. For example, diamond andgraphite are both allotropes of theelement carbon.

Bond A link between atoms.

39Y

Yttrium88.906

1H

Hydrogen1.008

* 29Cu

Copper64

Atomic number—thenumber of protons ( 6)in one atom

Chemical symbol ( 8)

Name ofelement

Atomic mass—the average mass of one atomcompared with the mass of one carbon atom.

11Na

Sodium22.990

19K

Potassium39.098

37Rb

Rubidium85.468

38Sr

Strontium87.62

55Cs

Caesium132.910

56Ba

Barium137.34

87Fr

Francium223

88Ra

Radium226.025

40Zr

Zirconium91.22

72Hf

Hafnium178.49

* 104Rf

Rutherfordium261

41Nb

Niobium92.906

73Ta

Tantalum180.948

* 105Db

Dubnium262

42Mo

Molybdenum95.94

74W

Tungsten183.85

* 106Sg

Seaborgium226

43Tc

Technetium97

75Re

Rhenium186.207

* 107Bh

Bohrium264

27Co

Cobalt58.933

28Ni

Nickel58.70

29Cu

Copper63.546

30ZnZinc

65.38

44Ru

Ruthenium101.07

45Rh

Rhodium102.906

46Pd

Palladium106.4

47AgSilver

107.868

48Cd

Cadmium112.40

76Os

Osmium190.2

77Ir

Iridium192.22

78Pt

Platinum195.09

79AuGold

196.967

80Hg

Mercury200.59

* 108Hs

Hassium277

* 109Mt

Meitnerium268

* 110Ds

Darmstadtium281

* 111Rg

Roentgenium272

* 112Cn

Copernicium285

* 113Uut

Ununtrium284

* 114Uuq

Ununquadium289

* 115Uup

Ununpentium288

* 116Uuh

Ununhexium292

* 117Uus

Ununseptium

* 118Uuo

Ununoctium294

5B

Boron10.81

6C

Carbon12.011

7N

Nitrogen14.007

8O

Oxygen15.998

9F

Fluorine18.998

2He

Helium4.003

10NeNeon20.179

18Ar

Argon39.948

36Kr

Krypton83.80

54Xe

Xenon131.30

86Rn

Radon222

13Al

Aluminium26.982

14Si

Silicon28.086

15P

Phosphorus30.974

16S

Sulphur32.06

17Cl

Chlorine35.453

31Ga

Gallium69.72

32Ge

Germanium72.59

33As

Arsenic74.922

34Se

Selenium78.96

35Br

Bromine79.904

49In

Indium114.82

50SnTin

118.69

51Sb

Antimony121.75

52Te

Tellurium127.60

53I

Iodine126.905

81Tl

Thallium204.37

82PbLead207.2

83Bi

Bismuth208.98

84Po

Polonium209

85At

Astatine210

57La

Lanthanum138.906

89Ac

Actinium227

58Ce

Cerium140.12

90Th

Thorium232.038

59Pr

Praseodymium140.908

91Pa

Protactinium231.036

60Nd

Neodymium144.24

92U

Uranium238.029

61Pm

Promethium145

93Np

Neptunium237.048

62Sm

Samarium150.4

94Pu

Plutonium244

63Eu

Europium151.96

* 95Am

Americium243

64Gd

Gadolinium157.25

* 96CmCurium

247

65Tb

Terbium158.925

* 97Bk

Berkelium247

66Dy

Dysprosium162.50

* 98Cf

Californium251

67Ho

Holmium164.930

* 99Es

Einsteinium254

68Er

Erbium167.26

* 100Fm

Fermium257

69Tm

Thulium168.934

101Md

Mendelevium258

70Yb

Ytterbium173.04

* 102No

Nobelium255

71Lu

Lutetium174.97

* 103Lr

Lawrencium260

10 11

57-71

89-103

The Periodic Table of elements is a list of all known elements arranged in orderof their atomic numbers (the number of protons in each atom). Thehorizontal rows are called periods, and the vertical columns are called groups.Elements with similar chemical properties ( 7) are placed in the same group. Eachelement has a higher atomic number than the element to its left. The Periodic Tablewas designed by Russian scientist Dmitri Mendeleev (1834-1907). Mendeleev leftgaps where he thought elements would be discovered in the future. He correctlypredicted the existence of germanium, gallium and scandium, which were alldiscovered in his lifetime. Of the 118 elements known to us, 94 occur naturally onEarth. The rest are produced artificially.

21Sc

Scandium44.956

3Li

Lithium6.941

4Be

Beryllium9.012

12Mg

Magnesium24.305

20Ca

Calcium40.08

22Ti

Titanium47.90

23V

Vanadium50.941

24Cr

Chromium51.996

25Mn

Manganese54.938

26FeIron

55.847

The lanthanide and actinide series (above, purple) are normally displayed belowthe rest of the Periodic Table. This is because they were discovered after the

table had been arranged, and by this time there was little room left in it.The arrows show where these elements should fit into the table.

Elementswith a star intheir top-leftcorner areproducedartificially

TTHHEE PPEERRIIOODDIICC TTAABBLLEE

Dmitri Mendeleev, creator of the PeriodicTable. Element number 101, mendelevium,is named after him.

Alkali metals ( 12)

Alkaline earthmetals ( 12)

Transition elements ( 12)

Semi-metals ( 12)

Halogens ( 8)

Noble gases ( 8)

Lanthanides ( 12)

Actinides ( 12)

Poor metals ( 12)

Other non-metals

A bicycle frame made from atitanium-steel alloy

Fireworkscontainmixtures ofpowderedmetals such asmagnesium.When they are setalight, they flare upwith bright colours.

Steel An alloy of iron and carbon ( 8).There are many different types of steelalloys, each containing slightly differentamounts of various elements, and eachdesigned to do a different task. Stainlesssteel is a mixture of steel, chromium, andsmall amounts of other metals. It is used

to make sinks and cutlery. Titaniumand vanadium steels resist hightemperatures without melting.

Alkaline earth metals A group of alkalimetals that have two electrons ( 6) intheir outer shell. Magnesium, calcium andradium are all members of this group.

Alloy A mixture of two or more elements,of which at least one is a metal. Alloys can be useful because they have differentchemical properties to the elements that make them up. For example, steel,made of iron and carbon, is muchstronger than iron.

Aluminium A light, soft metal that doesnot rust. It easily bonds with otherelements to make alloys that are lightweight and durable. It is the commonestmetal found in the Earth’s rocky crust.

Bronze A strong, shiny, brown alloy of tinand copper. Bronze was the first alloy tobe used by humans. It was used to make

weapons, tools and ornaments.

Metals are the largest group ofchemical elements ( 8), makingup about three-quarters of thePeriodic Table ( 10). Metals conductheat and electricity well compared tonon-metals. Most are solid at roomtemperature. They are strong, hard andtough, and can be polished to give asmooth, shiny surface. When they aresqueezed under great pressure, theychange shape and become squashed,rather than splinter apart or shatter.These features are true of most metals,but not all. For example, the metalsodium is very soft, while mercury is asilvery liquid at room temperature.

Copper A shiny, pinkish-brown metal.Copper is a good conductor ( 26) and isoften used to make wires and pipes.

Gold A soft, shiny, yellow element. Gold isoften found in small lumps, called nuggets.It is valuable because it is rare and does noteasily spoil or rust. It is a good electricalconductor ( 26) .

Iron A heavy, silvery metal. Iron is a popularconstruction metal because it is abundantand strong. It is used to make steel and canbe used as a magnet ( 26). Iron is a vitalelement needed by the human body: ironinside our red blood cells helps to carryoxygen around our bodies.

Precious metals Valuable metals such asgold, silver and platinum. They are prizedfor their rarity and for their beautifulappearance. They are often used to makejewellery and other ornaments.

Semi-metals Otherwise known as themetalloids, the semi-metals are a group ofelements that are neither metals nor non-metals. Typically they have the hard, shinyappearance of a metal, but make poorelectrical conductors ( 26). Arsenic andbismuth are both semi-metals.

Silver A soft, bright, shiny metal. Silver is aprecious metal, used to make ornamentsand jewellery. It is also a good conductorof electricity ( 26).

Mercury A silvery liquid metal. Mercury is the only metal that is a liquid at roomtemperature. It is used insidethermometers.

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

Ore Rock that contains metal compounds.

Poor metals The name sometimes givento a group of soft, weak metals that meltat low temperatures. Tin, lead andaluminium are all poor metals.

Plutonium A highly radioactive ( 7)metal. Plutonium is used to producenuclear energy ( 18).

MMEETTAALLSS

Lanthanides A group of silvery metalswith very high melting points. They aresometimes called the “rare earth metals”.They belong to the transition metals.

Lead A heavy, bluish metal that turns grey when exposed to the air and has a very low melting point. Lead is often made into weights because it is so heavy.

Battery casings are made of zinc.

! At present, there are 86 different metalsknown to us.

! Humans first started working metalsabout 8000 years ago. At first they usedcopper and gold nuggets that came out ofthe ground in their pure form. Bronze mayhave been discovered by accidentally mixingtin and copper. Because it could be madeharder, sharper and longer-lasting thanother metals, it could make far better toolsand weapons. It gave its name to the BronzeAge, which started in around 3000 BC.

! For many centuries lead was used tomake water pipes. It was then discoveredthat lead-contaminated water could causeserious illnesses. Copper or plastic is used tomake water pipes today.

! The purity of gold is measured in carats.Pure gold is 24 carats (24k). Gold that has

been mixed with other substances isabout 10k. Gold is often mixed with

copper or other metals to make itharder and more durable.

! Most cars have bodyworkmade of steel plate. This is strongand easy to shape, but steel ismostly iron, and iron rusts when

exposed to oxygen. Because ofthis, the steel panels receivean anti-rust coating beforethey are painted.

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Actinides A group of radioactive ( 7)metals. They are transition metals.

Alkali metals A group of metals that react with water to form alkaline solutions ( 14). All alkali metals have justone electron ( 6) in their outer shell. Theyare generally soft, shiny and a pale silverycolour. Lithium, sodium and potassiumare all members of this group.

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Tin A silvery metal that caneasily be bent and shaped.

Tin was once used to make cansand foil, but aluminium has since takenits place, because it is cheaper.

Transition metals A group of metals thatare mostly hard, dense and shiny and make good electricalconductors ( 26). Gold, silver, iron andcopper are all transition metals.

Zinc A bluish-white metal. It is used to make battery casings. Zinc is also an important part of our diet and isfound in foods such as nuts and red meat.

Magnesium A light, silvery-white metal.Magnesium easily reacts with otherelements and burns with a bright whiteflame. It is used to make fireworks ormixed with other metals to make alloysthat are strong but light.

The precious metals gold and silver

The steel bodywork of this carhas rusted due to exposure tooxygen in the air.

The Statue of Liberty in New York is made of a shell ofcopper built around an internal framework. Exposedto the air, copper develops a greenish covering. This isbecause it reacts with oxygen to form copper oxide.

Ingredients are mixed together tomake a cake. When the cake iscooked, its ingredientsare chemicallychanged.

Salt A solid compound made when a basejoins with an acid. A salt is a type of crystal( 8). Many types of salt dissolve in water.Table salt is called sodium chloride, butchalk (calcium carbonate) and saltpetre(potassium nitrate) are also types of salt.

Soluble The ability of one substance todissolve in another one.

Solution A liquid mixture of two differentsubstances. One substance, known as thesolute, usually a solid, is dissolved inanother substance, known as the solvent,which is usually a liquid. For example,table salt stirred into water is a solution.

Liquid oxygen andhydrogen areignited inside arocket engine.This is calledcombustion(right).

Mixture A blend of two differentsubstances that are not chemicallychanged by being put together.Sand and salt combined produce amixture—neither the salt nor thesand are chemically changed.

Neutralize To turn an acid or alkali intoa neutral solution—one that is neither acidnor alkaline. This can be acheived by mixingan acid and an alkali together. The aciddonates its positive hydrogen atom to thenegative alkali, so that they both have a neutral charge ( 26).

Oxidation A reaction in which oxygencombines with another chemical.

Physical reaction A change in a substancethat affects its appearance but not itschemical properties ( 7). Crushing a can and melting an ice cube are both examplesof physical reactions. The can changesshape and the ice changes state, but theyare otherwise unaltered.

Reactive How likely a substance is to join with another substance in a chemical reaction.

Reversible change A change, or reaction,that can be undone. If you freeze water,you can reverse the change by melting theice. If you dissolve salt in water, you can boiloff the water to leave the salt. Reversiblechanges never create new substances.

Diffusion The process by which moleculesmove around to fill a space. For example,molecules of ink will diffuse, or spread out,in a glass of water so that the liquidchanges colour.

Electrolysis The process of separating theelements in a compound ( 8) by using an electrical current ( 26). The compound must be in a liquid state for thisto happen.

Filtration A way of removing solids fromliquids by pouring a mixture through amaterial known as a filter. This is a materialwith very fine holes in it. It allows liquids,but not solids, to pass through it.

Indicator A substance that shows howacidic or alkaline a solution is. Universalindicator and litmus paper are bothexamples of indicators. They change colourdepending on the acidity of a solution.Acidity is measured using the pH scale. Avery acidic solution has a pH of 0. A veryalkaline solution has a pH of 14. A neutralsolution (such as water) has a pH of 7.

Alkali A base that dissolves inwater. An alkali is a substancethat has an overall negativecharge ( 26). It is always

willing to give up an electronor receive a proton in order to

become neutral. This means thatit readily reacts with other

substances. All alkalis are bases.

Base A substance that reacts with anacid to form a salt and water.

Catalyst A substance that triggers orspeeds up chemical reactions.

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

Concentration A measure of how strong asolution is.

Corrosion The breaking down of asubstance into the individual atoms thatmake it up. This is caused by a chemicalreaction between the substance and itssurroundings. For example, steel ( 13)corrodes when it is exposed to oxygen inthe air.

Achemical reaction takes place whenone substance joins with another toform a completely new substance.Chemical reactions are taking place allaround us. Some happen naturally. Forexample, the food we eat is chemicallychanged inside our bodies to produceenergy. Other reactions are made to takeplace artificially, for example in themanufacture of medicinal drugs.

Acid A substance that contains apositively-charged ( 26) hydrogen atom(ion). An acid will always give up itshydrogen ion in order to rid itself of itspositive charge and become neutral.Alternatively, it can accept anelectron, which is negative, toachieve the same result. Thismeans that acids readily reactwith other substances.

Chemists wear goggles, labcoats and gloves toprotect themselves from corrosive chemicals.Strong acids and alkalis can dissolve substances,including human skin and even bones.

! The speed at which a reaction takes placeis called its rate of reaction. Many reactionstake place more quickly at highertemperatures or in bright light, becausetheir molecules are given more energy.

! In the Middle Ages the plague killedmillions of people. The dead bodies of itsvictims were sprinkled with lime, a strongand corrosive base. It helped to make themrot faster and to kill harmful germs.

! A bee’s sting is painful because it isacidic. The pain can be treated by using analkaline solution of ammonia, whichneutralizes the acid in the sting.

! Citrus fruits, such as oranges, lemonsand grapefruits, all contain a natural

citric acid. This gives them a sharpor sour taste. A weak alkali has abitter or soapy taste.

Irreversible change A change, or reaction,that cannot be undone. When you bake acake, the molecules in its ingredients arerearranged. You cannot change the cakeback into its ingredients. Burning is anothertype of irreversible change. Irreversiblechanges always produce a new substance.

CCHHEEMMIICCAALLRREEAACCTTIIOONNSS

The fumes from vehicle exhausts and factoriescontain nitrogen dioxide and sulphur dioxide.These dissolve in drops of water in clouds to formnitric or sulphuric acids which fall as acid rain. Thiscan seriously damage buildings and statues.

The sea is a solution of salt. The Dead Sea has somuch salt in it that no more can dissolve—it is asaturated solution. Because it cannot dissolve, solidlumps of salt float on the surface.

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Miscibility The ability for liquids to mixtogether. Miscible liquids mix easily.Immiscible liquids, for example oil andwater, will not mix. If an emulsifier isadded, immiscible liquids will floattogether in a mixture called an emulsion.

Machine A device that changes thedirection or size of a force, making it easierto perform certain tasks. The most simplemachines are: a wheel, a lever, a wedge, ascrew, a pulley and an inclined plane.

Momentum The tendency for objects that are moving to carry on moving. Anobject’s momentum is a result of its massand its velocity.

! The Earth’s gravitational force is whatgives all objects on Earth their weight.

! The Moon has less mass than the Earth,so its gravitational force is less. On the Moonthis book would weigh about one-sixth ofwhat it weighs on Earth.

! Even still objects exert forces. When yousit on a chair, the chair pushes up against youwith the same force as your weight pushesdown on the chair. If this did not happen, thechair would collapse beneath you.

! Birds and fish have naturally streamlinedbodies. Their shape minimizes the flow of airor water around them, which reducesfriction and allowsthem to movefaster.

! It is said thatIsaac Newton firsthad the idea forgravitational forcewhen he saw anapple fall from atree, andquestioned why itfell straight to theEarth.

Aforce is something that changes themovement or shape of an object.Once an object is set in motion, itwill carry on moving at the same speed andin the same direction until another forcespeeds it up, changes its direction or slowsit down. Forces always act in pairs. Whenboth forces are equal, an object will staystill or will move at a constant speed in onedirection. When one force is greater thanthe other, the forces are unbalanced andthe object will change direction or speed.When several forces act on an object, theoverall effect is called the resultant force.For example, lift, thrust, gravity and dragall act on an aeroplane, while its resultantforce is a forward motion.

FFOORRCCEESS &&MMOOTTIIOONN

Nuclear force The force that bindsneutrons and protons together inside thenucleus of an atom ( 6).

Pressure The amount of force acting on acertain area.

Reaction A force that opposes anotherforce of equal strength. Forces always actin pairs, where one force is called theaction and the other is called the reaction.

Thrust The force from a vehicle’s enginethat results in forward motion.

Velocity How quickly an object changes itsposition. Velocity measures both howquickly an object moves and the directionin which it travels. Speed measures howquickly an object moves, but does notspecify its direction.

Weight A measure of the gravitationalforce pulling on an object. A big book isweighty because it is pulled downwards bythe Earth’s gravity. In space, away from theEarth’s gravity, objects and people are notpulled down, so they become weightlessand float about freely. Objects in space stillhave mass, however.

The two pairs of forces actingon a flying plane are: lift andthrust, and gravity and drag.The plane flies because theforces are balanced.

Motion The word given to any kind ofmovement. All movement is caused byforces. An object going in a straight linehas linear motion. An object that circles acentral point has circular motion. Anobject that twists around on the spot hasrotary motion. An object moving to and frohas reciprocating motion.

Newton, Isaac (1643-1727) The Britishscientist who discovered the laws ofgravity and motion. Newton proposed thatthe Earth’s gravity attracted the Moon andkept it circling the Earth.

Newton The unit in which force ismeasured. One newton is the force of theEarth’s gravity on an object with a mass of102g (about the size of a small apple).

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Gravity The force that attracts all objects toeach other. The larger an object’s mass, orthe greater its density ( 6), the greater itsgravitational pull. The greater the distancebetween objects, the smaller the force ofgravity between them. When we jump inthe air, gravity is the force that pulls us backto the Earth.

If a bus suddenly stops moving, people on it fallforward because of their momentum.

Fulcrum

Wheels haverotary motion.

Gravitationalforce pulls youdown a slide.

When you sit on aroundabout, you areaffected by bothcentripetal andcentrifugal forces.

Neither the dog nor his ownercan move because they are bothpulling with the same force.

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Isaac Newton

Thrust

Drag

Lift

Gravity

A lever is a stiff bar thatpivots at a fulcrum. If thefulcrum is near one end, asmall force at the other endwill move a heavy weight.

A rope and pulley (left) and a lever(below) are both types of machine.

A rope and pulley changesthe direction of a pullingforce so that you pull downon a rope in order to movea weight upwards. This isbecause it is easier to pulldown than to pull up.

Pulley

Inertia The tendency for objects to resistchanges to their motion; that is, thetendency for objects that are moving tocarry on moving, and for objects that arestill to stay still. All objects always haveinertia, whether they are moving or still.

Lift An upward force that holds aircraft inthe air. As an aeroplane moves, the shapeof its wings forces air to flow faster overthe top of the wing than the air flowingbeneath it. This means that there is lesspressure on the upper side of the wingthan on the lower side. The result is lift.

A “Chair-o-Plane”

Acceleration The measure of how quicklyvelocity increases. A decrease in velocity iscalled deceleration.

Centrifugal force The force that seems topush outwards on an object moving in acircle. When we sit on a spinning fairgroundride such as a “Chair-o-Plane” (below) wefeel centrifugal force pushing us outwards.At the same time there is another force atwork, keeping us moving in a circle. This iscalled the centripetal force.

Centripetal force The force that pullsinwards on an object moving in a circle. Itbalances centrifugal force. Gravity is atype of centripetal force that keeps theplanets moving around the Sun.

Drag A force that slows an object down asit travels through a gas or liquid. Dragoccurs because of friction between theobject and the molecules around it. Unlikefriction, drag is affected by an object’sspeed. Drag that takes place in the air iscalled air resistance. Drag that takes placein a liquid is called water resistance.

Friction A force that tries to stop thingsmoving. Friction is produced when twosurfaces rub together. Rough surfacesproduce more friction than smooth ones.Friction can make machines wear out, but

it can also be helpful. For example, avehicle stops because of

friction provided by itsbrakes.

Chemical energy The energy that keepsatoms bonded together ( 6). We makeuse of chemical energy in fuels. As the fuelburns, the bonds between atoms arebroken, which releases energy.

Fossil fuel A fuel formed from the remainsof living things that died millions of yearsago. Coal, oil and natural gas are all typesof fossil fuel.

Fuel Any source of energy.

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

Hydroelectric energy Energy that comesfrom the kinetic and potential energy ofmoving water. Hydroelectric powerstations control the rush of water througha dam. The movement of the water isused to generate electricity.

Energy is the ability to make thingshappen, cause change and carry outwork. Energy is all around us, inmany different forms, including heat ( 24),light ( 22), sound ( 20), chemical, kineticand electrical energy ( 26). Energy canchange from one form to another, orstored waiting to be used—it is never lostor gained. For example, different energiesare converted into electrical energy, whichis useful in our modern world. This processis called generating electricity. Withoutenergy, our world would be completelydark and silent.

EENNEERRGGYY

Work The energy transferred when aforce ( 16) moves an object over adistance. For example, you have to workto lift a box. You must exert a force onthe box to overcome the Earth’sgravitational pull ( 16). In order to do thisyou must first have energy, which youobtain in the form of chemical energyfrom your food.

Joule The unit used to measure energy.One joule (J) is the energy exerted whena force of one newton ( 17) moves anobject a distance of one metre.

Kinetic energy The energy that anobject has because of its movement. Forexample, a ball rolling down a hill haskinetic energy. The faster it rolls, themore kinetic energy it has.

Non-renewable energy Energy sourcesthat will eventually run out and cannotbe replaced for hundreds of millions ofyears. Oil and coal are both examples ofnon-renewable energy sources.

Nuclear energy The energy contained by an atom, due to the strong force that holds together the protons andneutrons in its nucleus ( 6). There are two ways of releasing nuclearenergy. These are: nuclear fission andnuclear fusion. They are both forms ofnuclear reaction.

This energy chainshows howenergy canchange form.Heat and lightenergy from theSun make foodcrops grow.

Nuclear fission The process of splittingopen the nucleus of an atom by blasting itwith a high-speed neutron ( 6). Thisreleases a huge amount of nuclear energy.

Solar energy The heat and light energythat is given off by the Sun. A solar cellis a device that converts solar energy into electrical energy when the cell isexposed to sunlight.

Watt The unit used to measure power—the speed at which energy is converted.One watt (W) of power is the same as onejoule (J) of energy per second.

! The word energy comes from the Greekword energia, which means “activity”.

! One wind turbine can generate enoughenergy to power heat and electricity in upto 300 homes. People have been usingwind energy since ancient times, whenwindmills were used to grind grain.

! In just one hour, enough sunlight fallson the Earth to power every home on theplanet for a whole year.

! When you run, your muscles onlyconvert about 25% of the chemical energyfrom your food into kinetic energy to keepyou moving. The rest is lost as heat energy.

Nuclear fusion The process of fusingtogether the nuclei of two atoms. This releases an enormous amount ofnuclear energy.

Potential energy Energy that is stored.For example, a boulder on a hillside haspotential energy. As the boulder starts to roll under the force of gravity ( 16), its potential energy changes into kinetic energy.

Power The rate, or speed, at which energyis converted or work is done. Power ismeasured in watts.

Renewable energy Energy sources thatwill not run out because they areconstantly replenishing themselves. They come from natural sources, such as sunlight, waves, tides, wind andgeothermal heat.

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NUCLEAR FISSION: A nuclear particle called aneutron smashes into the nucleus of a uraniumatom (1). The nucleus breaks into two parts (2).This releases heat and other energy alongside twomore fast-moving neutrons (3). These smash intomore uranium nuclei in a chain reaction (4).

The Hoover Dam in the United States is ahydroelectric power station. A lake is formed bydamming a river in a steep-sided valley. Some of thewater is allowed to rush out through pipes and themovement is used to generate electricity.

Food crops store energyfrom the Sun in the form ofchemical energy. When we eat weabsorb this energy into our bodies.When we move, our muscles convertchemical energy into kinetic (movement) energy.

In this scene, there are examples of differentkinds of energy at work .

The onlookers encourage therunners with sound energy.

The runners usekinetic energy.

Cameras use lightand electricalenergy.

The Sun produces heat andlight energy.

Planes use chemicalenergy from the fuelburnt in their engines.

A wind farm out at sea is used to harness windenergy and generate electricity.

1918

SSOOUUNNDD Echo The sound we hear when soundwaves bounce off a surface.Echolocation A type of sonar used byanimals such as bats and whales. Theanimals emit sounds and listen to theirechoes in order to locate solid objects.Echolocation allows animals to hunt indark or murky conditions where it isdifficult to see.

Musical instrument An object that is usedto make musical sounds. In a cello, a bowrubs over the cello’s strings to make themvibrate. The vibrations pass into the airand also to the cello’s hollow body,making the sound louder and richer.

Noise Any kind of sound. Noise is oftenused as a word for unwanted sounds.

Pitch How high or low a note is. High-pitched sounds have high frequencies andlow-pitched sounds have low frequencies.

Resonance The frequency at which anobject will vibrate if you hit it. This issometimes called the natural frequencyof an object.

Reverberation The sound heard whensound waves continue to travel after theoriginal source of a sound has gone.

Sonar (SOund Navigation And Ranging)A technique that uses sound waves todetect solid objects. The sound wavesbounce off them and reveal their position.Ships use sonar to find shoals of fish orother ships.

Speed of sound The speed at which soundtravels. Sound travels through air at about343 metres per second. The speed ofsound varies depending on the substanceit travels through. Loud and soft soundsall travel at the same speed.

Volume The loudness of a sound. Volumeis measured in decibels (dB). Some soundsare so quiet that we can only just hearthem. Others are so loud that they maydamage our ears. (See intensity.)

Wavelength The distance between onesound wave and the next. Sound waveswith short wavelengths have highfrequencies and make high-pitchedsounds. Sound waves with longwavelengths have low frequencies andmake low-pitched sounds.

! Whales and dolphins use sound tocommunicate. Whalesong can travel up to800 km under water. Whales are believedto be the loudest animal in the world. They can make sounds as loud as 188 dB.The loudest land animal is the howlermonkey. Its calls can be as loud as 88 dB and can be heardup to 16 km away.

! Sound wavescan only travelthrough matter.Space iscompletely silentbecause there areno gas moleculesfor sounds to passalong.

! Most sounds onlycarry a relatively smallamount of energy. Thesound of 200 pianosplaying togetherproduces about thesame amount of energyas it would take to lightone light bulb.

Sound is a form of energy ( 18) madewhen objects vibrate (move to and frorapidly). As an object vibrates it sets theair around it vibrating too: molecules ofthe gases in the air press close togetherand then pull apart. These regions ofhigher and lower air pressure are calledsound waves. They move away from thesound source in all directions, like ripplesin a pond. Sounds also travel as vibrationsthrough liquids and solids. The moleculesare closer together in liquids and solidsthan in gases, so sounds travel throughthem much faster.

Infrasonic Sounds that are too low-pitchedfor humans to hear. It is thought that someanimals are able to hear them.

Intensity The amount of energy that soundwaves carry. The intensity of sound wavesdetermines their volume.

Music A form of art using pleasant sounds.

Acoustics The study of how sound isaffected by location, for example, howsound bounces around a concert hall.

Amplitude The height of a wave. Soundwaves with high amplitudes make loudsounds and sound waves with lowamplitudes make quiet sounds.

Decibel The unit used to measure thevolume, or intensity, of sounds. A veryquiet sound, such as the rustling of leavesis about 20 decibels (dB). A very loudsound, such as a rocket taking off, is about120 dB. Sounds over 80 dB can damageyour ears.

Frequency The number of vibrations, orsound waves, per second. Sound waveswith high frequencies make high-pitchedsounds. Sound waves with lowfrequencies make low-pitched sounds.

Hertz The unit used to measurefrequency. One hertz(Hz) is one vibrationper second.

Stringedinstruments

Sound travels quickest through solids, slowerthrough liquids and slowest of all through air.

The Bell X-1 rocket plane was the firstaircraft to fly faster than the speed of sound.

Sound waves traveloutwards from their sourcelike ripples on a pond.

A trumpet producessound waves.

Supersonic Faster than the speed ofsound. When objects travel faster thanthe speed of sound the they make a loudnoise called a sonic boom.

Ultrasound Sounds that are too high-pitched for humans to hear. Someanimals, such as dogs and bats, can hearthem. An ultrasound scanner is used tomake images of inside the human body. Itbeams high-pitched sound waves into thebody. A computer transforms the echoesinto an image.

Water (1530 mper second)

Air (343 mper second)

Steel (5050 mper second)

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An ultrasound scan of a baby in the womb

A watch makes a soft,medium-pitched sound.

Bats useecholocation totrack their prey.

A rocket makes a loud,low-pitched sound.

A singer makesa medium-loud,medium-pitchedsound.

The sound made by a jet enginemeasures about 140 dB, but it canonly be heard faintly from thestreet because it is so far away.

An electric drill makes a sound ofabout 100 dB. The people that useit must wear ear-protectors.

The sound made by busy traffic canregister between 70 and 80 dB.

The sound of a carhorn can be up to110 dB.

The colour wheel shows howthe different colours of lightadd up to make white light. Whenyou spin the wheel, the colours whirlaround so fast that the eye cannotfollow them. Inside the eye each colourmerges with the others so the eye sees allthe colours at once—and all colours oflight added together make white light.

Female glow-worms(a type of beetle)emit light when they are ready to mate.

A rainbow shows allthe different colours

of the spectrum.

Spectrum of light The section of theelectromagnetic spectrum ( 28) that wecan see. It is formed of all the differentcolours that make up white light: red, orange, yellow, green, blue, indigoand violet.

When the three primary colours of light, red, blueand green are added together they make white light.

Speed of light The speed at which lighttravels through empty space. This is about300,000 km/s—about seven and a halftimes around the Earth in one second. Thespeed of light is the speed limit for theUniverse: nothing can travel faster.

Translucent A material that allows light topass through it, but which spreads thelight rays out in all directions. We canmake out shapes behind translucentmaterials but we cannot see them clearly.Tracing paper and ice are both translucent materials.

Convex lens A shaped piece of glass orplastic that is thicker at its centre than atits edges. It brings light rays together at asingle point called a focus. When you lookthrough a convex lens, objects appearlarger than they really are.

Diffraction The spreading out of light raysas they pass through a narrow gap.

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

Lens A shaped piece of glass or plasticthat bends light rays.

Light filter A piece of coloured,transparent plastic or glass that allowslight of its own colour to pass through it,but stops all other colours. Light filters areoften used in stage lighting, to change thecolour of a light. If a blue filter is placedover a white light, the light that shines onto the stage will be blue.

Luminescence Light that is createdat low temperatures, usuallycaused by certain chemical reactionsor electricity.

Mirage A trick of the eye, that makesfar away objects look much closer thanthey really are. Mirages happen whenlight from the sky is reflected off a layerof hot air just above the ground or thesea. They are commonly seen in deserts.

! It takes sunlight more than eightminutes to travel nearly 150 million km fromthe Sun to the Earth.

! In one year, light travels 9.46 trillion km.This distance is called a light year.

! The colour of an object depends onwhich colours it absorbs and which itreflects. For example, a leaf looks greenbecause its surface absorbs all the colours inwhite light, except green, which it reflects.

! The eye contains a natural convex lenswhich focuses an image on to the retina atthe back of the eye.

! Concave lenses are used in glasses forpeople who are short-sighted (they havedifficulty seeing objects far away fromthem). Convex lenses are used for peoplewho are long-sighted (they have difficultyseeing objects close to them).

Light is a kind of energy ( 18) that oureyes can detect, enabling us to see. Itis mostly produced by very hotthings. It travels in straight lines, but it canreflect (bounce) off objects. In fact, wecan only see an object when light reflectsfrom it and into our eyes, or if it produceslight itself. Sunlight is not colourless, but ismade up of all the colours of the rainbow:the spectrum of light.

LLIIGGHHTT &&CCOOLLOOUURR

Prism An angled block of transparentmaterial such as clear glass or plastic. Aslight waves pass through a prism, theychange speed and are bent, or refracted.Longer waves of red light refract least.Shorter waves of violet light refract most.The other colours of the spectrum spreadout in between.

Rainbow An arch of colours that formsacross the sky when the Sun shines frombehind you at rain falling in front of you.The raindrops act as millions of tinyprisms, each splitting the white light in sunlight into every colour of the spectrum.

Reflection The bouncing of light rays offan object. Smooth, shiny, light surfacesreflect more light than rough, dark ones.

Refraction The bending of light rays asthey travel through different transparentmaterials. This occurs because light travelsat different speeds through differentmaterials. At the boundary between twomaterials, the light changes speed and isbent from its straight path.

Shadow A dark shape or area producedwhen an opaque object stands between asurface and a source of light. Shadows areformed because light can only travel instraight lines and cannot bend around theopaque object.

Mirror A sheet of glass with a thin layer of metal on the back. Mirrors formimages by reflecting light from the surfaceof the metal.

Opaque A material that does not allowlight to shine through it.

Pigment A substance that is added toanother substance to give it colour.

Primary colours Any of the threecolours that can be mixed together

to form all other colours. The primarycolours of light are red, green and blue.They can be mixed to make any colour.When all three are mixed together theymake white light. In paints, which containpigments, the primary colours are red,yellow and blue.

A prism refracts whitelight, splitting it into everydifferent colour of thespectrum.

Light is producedin a bulb when thefilament is heatedby an electricalcurrent.

Bioluminescence The ability of someanimals to produce light. The light isgenerated by chemical reactions ( 14) inthe animal’s body.

Concave lens A shaped piece of glass orplastic that is thicker at its edges than atits centre. It makes light rays diverge(spread out). When you look through aconcave lens, objects appear smaller thanthey really are.

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Filament

Transparent A material that transmitslight, or allows light to pass through it. Wecan easily see through transparentmaterials, such as glass. We can see theglass because a tiny amount of light isreflected off the material.

By placing two mirrors in a tube you can make aperiscope, a device used to see around corners.Light coming in at one end is reflected through tothe viewer at the other end.

A magnifying glass isa convex lens.

A concave lens (top) and convex lens (bottom).

Birds glide in the convection currents that riseoff warm areas of land and sea.

Above: a thermogram of an elephant

Fahrenheit scale One of the scales used tomeasure temperature. In the Fahrenheitscale, 32 degrees Fahrenheit (32°F) is thetemperature of freezing water and 212°F is the temperature of boiling water.

Kelvin scale Sometimes known as theabsolute scale, the Kelvin scale is one ofthe scales used to measure temperature.It starts at absolute zero, or 0 K. Thetemperature of freezing water is 273 Kand the temperature of boiling wateris 373 K.

Radiation One of the ways in which heatmoves. Radiant heat travels in the form of waves. Unlike conduction andconvection, radiation can travel throughempty space (a vacuum). This is how theSun’s heat reaches the Earth.

Temperature A measure of howmuch heat energy a substance or anobject possesses.

Thermals Pockets of warm, rising air inthe Earth’s atmosphere. They rise fromareas of sea and land that have beenrecently warmed by the Sun.

Thermal conductor A substance that heatcan travel through easily. Most metals aregood thermal conductors.

Thermal insulator A substance that slowsdown the movement of heat. Air, woodand plastic are all good thermal insulators.

Thermodynamics The study of heat andhow it can be changed into differentforms of energy.

Thermogram A type of photograph thatshows areas of different temperatures indifferent colours. Typically the hottestareas appear white and the coolest areasappear black.

! Like light, radiant heat can reflect from surfaces.

! On a hot day, light-coloured clothesreflect the Sun’s warmth and keep youcooler than dark clothing, which absorbswarmth. In very hot countries, people painttheir houses white so that they reflect heat.

! Air acts as a thermal insulator. Layers ofclothing trap air between them, helping tokeep you warm.

! The faster an aircraft goes, the hotterits outer surface will become due to friction ( 16) with molecules in the air. Veryfast planes have special heat-radiating paintthat gives out heat as fast as possible. This prevents the metal skin of the planefrom melting.

! Normal human body temperature isabout 37°C. If body temperature falls belowthis temperature, fatal hypothermia may set in.

Heat is a type of energy that objectspossess when their atoms aremoving or vibrating. It issometimes called thermal energy. Themore an atom moves, the more heat ithas. Heat moves around and betweenobjects in three main ways: conduction,convection and radiation. Heat willalways move from a hot area to a coldone. Temperature is not the same as heat.It is a measure of how much heat energysomething possesses.

Absolute zero The lowest temperaturepossible. At absolute zero, an object’satoms would be absolutely still and notvibrate at all. Absolute zero is zero on the Kelvin scale. It is -273.15°C in the Celsius scale.

Convection One of the ways in which heatmoves. Convection only occurs in fluids(liquids and gases). As some of the atomsin a fluid receive heat, they gain energyand spread out. The hot part of the fluidbecomes less dense than its coolersurroundings and rises upwards. But as itrises, it moves away from the source ofthe heat, so cools down and sinks.

Convection current The circulation ofheat produced when a liquid or gas risesand sinks as it repeatedly heats up andcools down.

Penguins are kept warm by their natural insulation:feathers and a thick layer of fat, called blubber.

Even rocks melt at above 800°C or higher. The liquidrock that spurts from volcanoes is called lava.

Conduction One of the ways in which heatenergy moves. In conduction, heat passesbetween two objects that are in physicalcontact. When you touch an object to seehow warm it is, you receive some of itsheat by conduction.

Below: the temperature in space varies hugelybetween areas of sunlight and shadow. Astronautswear suits that regulate their temperature. Shinyfoil reflects the intense heat of the Sun. Insulationinside the suit stops the astronauts from freezing.

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Celsius scale One of the scales used tomeasure temperature. Zero degreesCelsius (0°C) is the temperature offreezing water and 100°C is thetemperature of boiling water.

Cold The absence of heat. Objects thatare cold have very low temperatures.

Thermometer An instrument used tomeasure temperature. Glass thermometersare made of a long glass tube containingalcohol or mercury, which expands as itheats, and rises up the tube. Digitalthermometers have small electric sensorsthat record changes in temperature.

HHEEAATT && TTEEMMPPEERRAATTUURREE

Heat travels in three ways:1 Radiation: heat travels in theform of waves.2 Conduction: heat energypasses between two objects thatare touching. 3 Convection: heat energymoves through a gas or a liquid,rising up as the hot atomsbecome less dense.

1

2 3

11.2°C

0.0°C

2

4

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10

You can make staticelectricity by

running a combthrough yourhair. The combleaves some of

its electrons inthe hair.

Voltage The unit used to measureelectrical force. Voltage (V), or volts,measure the force needed to pushelectrons around a circuit.

Voltmeter An instrument used to measure voltage.

Electricity flows freely in metals, as electronsdetach from their atoms easily. In anelectric current, electrons are forced tomove in the same direction.

A lightning conductorleads electrical charge

down a rod awayfrom the building. Solenoid A coil of wire that acts as a

magnet when electricity is passed through it.

Static electricity Electricity that does notmove. Static electricity is produced whenelectrons are separated from their atoms.It builds up when electrons rub off fromone material on to another. The materialthat has lost electrons becomespositively charged; the materialthat has gained thembecomes negativelycharged.

Having lostsome electrons,the comb nowhas a positivecharge. It canpick up smallpieces of paperbecause it attractsthe electrons in thepaper’s atoms.

Ampere The unit used to measure thestrength of an electric current. Amperes(A), or amps, measure how many electronspass a certain point in one second.

Battery An object that converts chemicalenergy into electrical energy. When abattery is connected to a circuit, chemicalreactions inside it push electrons out ofone end, around the circuit, and back tothe other end of the battery.

Circuit A pathway along which an electriccurrent can flow, for example, a wirejoining a battery and a light bulb. If there isa gap in the wire, the circuit will be brokenand the current will stop flowing. Switchesturn electrical appliances off by breakingthe connections in a circuit.

Current electricity Electricity that flowsfrom one point to another.

Direct current An electric current thatalways flows in one direction. Batteriesproduce direct current.

Electrical charge Atoms are made up ofsubatomic particles called protons,neutrons and electrons. Electrons have anegative (-) electric charge and protonshave a positive (+) electric charge.Neutrons have no charge at all.

Electric conductor A substance thatelectricity can easily flow through. Metalsare good conductors because metal atomscontain electrons that are free to move.

Magnetic poles The two points at eitherend of a magnet, called the north andsouth poles. Lines of magnetic force runbetween opposite poles.

Magnetism The invisible force of attractionor repulsion between magnetic materials.

Resistance A measure of how easilyelectrons can flow through a material.Good conductors have low resistance,meaning that electrons can pass alongthem quickly and easily. Resistance ismeasure in units called ohms (Ω).

Semiconductor A substance whoseresistance lies half way between that of aconductor and that of an insulator.

! When lightning passes from clouds tothe ground, the amount of electric energyproduced can be enough to destroy abuilding or kill a person. A lightningconductor can be used to prevent accidents.This is a metal rod that runs from the top ofa tall building to the ground. It leads theelectric charge down the rod and awayfrom the building to the ground, spreadingthe electricity over a wide area.

! The first magnets were calledlodestones. A lodestone is a naturallymagnetized pieceof themineralmagnetite.Lodestoneswere used inancient times asprimitive compasses.

Electricity is a form of energy madeby the movement of electrons ( 6),the negatively charged particlesfound inside atoms. Electricity flowswhen electrons are free to move fromone atom to another. It is easily changedinto other forms of energy and is easy touse because it can be directed alongwires. Magnetism is a force that attractssome objects to other objects. An objectwith a magnetic field is called a magnet,and is usually made of the metal iron.Electricity can produce magnetism andmagnetism can produce electricity.

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Magnet An object that has two ends,called poles, and a force of attractionbetween them. Most magnets are madeof the metals iron or steel and attractother objects made of these materials.The Earth itself has a magnetic field, as if ithad a magnet inside it. Magnets have noeffect on wood, plastic, or most otherkinds of metal.

Magnetic compass An instrument that hasa small needle-shaped magnet balancedinside it. The ends of the needle areattracted to the Earth’s magnetic poles,so that one end always points due North.

Magnetic field The region surrounding amagnet where the effects of the magnetcan be felt.

A magnetic field moving near a wire causeselectricity to flow in the wire (top). An electriccurrent flowing in a wire creates a magnetic fieldaround the wire (bottom).

Electric current The flow of electricitythrough a conductor.

Electric insulator A material that reduces orstops the flow of electricity. Substancessuch as wood, plastics, rubber and glassmake good insulators because the electronsinside their atoms do not easily move.

Electromagnet A temporary magnetproduced by sending an electric currentalong a wire. If the wire is twisted into a coilit will produce a stronger magnetic fieldbecause the field around each loop of wirecombines. The magnet can be turned on andoff by switching the electricity on and off.

Electromagnetism Magnetism producedusing an electric current.

Generator A machine, sometimes known as a dynamo, that uses movement togenerate electricity.

Lightning A visible spark of static electricityproduced during a thunderstorm. Staticelectricity builds up inside clouds when iceand water molecules bump against eachother and become electrically charged. Thelight we see is a strip of air being suddenlyheated by the electricity. The heat of theflash makes the air around it expand so fastit makes a loud boom of thunder.

A large electromagnet is used to lift metal objectson a scrap heap.

An electrical circuit of battery, wires and bulb.

EELLEECCTTRRIICCIITTYY&& MMAAGGNNEETTIISSMM

A sprinkling of tiny pieces of iron around a magnetshows the pattern of its magnetic field.

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Electrons

A compass

Alternating current An electric currentwhere the flow of electrons regularly

changes direction. This type of currentis produced in power stations.

Ammeter An instrument usedto measure amperes.

Metal atom

Magnet

Ammeter

Battery

Magnetic field Solenoid

Infrared (IR) radiation A form ofelectromagnetic radiation, with awavelength just longer than that of visiblered light. It is the radiation that you feel asheat from hot objects. IR radiation is usedfor short-range communications, such asin television remote controls and remotelocking in cars.

Maxwell, James Clerk (1831–1879) Scottishphysicist who discovered the existence ofelectromagnetic waves.

Electromagnetic radiation A form ofenergy that travels in waves at the speedof light. Unlike other forms of energy, suchas sound waves, radiant energy can travelthrough empty space (a vacuum).

Gamma rays A form of electromagneticradiation with a very high frequency andshort wavelength. They are given out by

radioactive atoms ( 6) or produced innuclear reactions ( 18). They can pass

right through some substances.

Ultraviolet (UV) radiation A form ofelectromagnetic radiation with awavelength just shorter than that of visibleviolet light. Some of the energy emitted bythe Sun takes the form of UV radiation.Most UV rays from the Sun are absorbedby the Earth’s atmosphere, but they stillcause tanning of the skin and sunburn.

Microwaves A form ofelectromagneticradiation with a

wavelength longer thaninfrared radiation. Microwaves

are used in communications. Somemicrowave frequencies can also be

used in cooking.

Photons Light and other forms ofradiant energy can either be

thought of as waves or as tinyparticles, called photons. Photons have

no mass or electrical charge ( 26). Theytravel at the speed of light.

Radar (RAdio Detection And Ranging)A system that detects objects bytransmitting radio waves and receivingthe “echoes” that bounce back fromthem. Radar is used by ships andaeroplanes to detect other craft oroncoming storms.

Radio waves A form of electromagneticradiation with a very long wavelength.Radio waves are important incommunications through air and space.

Röntgen, Wilhelm (1845–1923) Germanphysicist who discovered X-rays.

Transmitter An electronic device thatsends out electromagnetic waves, such asradio waves.

! Overexposure to ultraviolet radiation from exposure to the Sun cancause skin cancer.

! The longest waves in theelectromagnetic spectrum are over 100 kmlong. The shortest waves are only a billionthof a millimetre long.

! Although ultraviolet and infrared raysare invisible to humans, some animals cansee them. Bumblebees are able to seeultraviolet light and snakes have pits neartheir eyes that can detect infraredradiation. This means thatsnakes can hunt in thedark becausethey can detectobjects that give off heat,such as the warm-blooded mammals on whichthey prey.

X-rays A form of electromagneticradiation with very short wavelengths andextremely high frequencies. They passright through some solids. In medicinethey can be used to see the structure ofbones and internal organs by placing apatient between an X-ray source and aphotographic film or camera.

Some banknotes are printed with an ink that onlyshows up under a special UV light bulb. Bankers cancheck for fake notes by using one of these lights.

Microwave oven

RADIO WAVES

Radio

The wavelength at the left handof the spectrum is a millionmillion times the wavelength atthe right hand end.

MICROWAVES

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X-RAYS

Sunbathing (ultraviolet radiation)

X-ray machine

VISIBLE LIGHT

INFRAREDRADIATION

Television remotecontrol (infrared)

ULTRAVIOLET RADIATION

Visible light The part of theelectromagnetic spectrum that is visibleto the human eye. Light waves withslightly different wavelengths appear asdifferent colours. The colour red has thelongest wavelength and violet has theshortest wavelength.

Some space probes use radar to map the surface ofplanets. Instead of light, radio waves are used tobuild up an image of the planet’s landscape.

Bumblebee

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GAMMA RAYS

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The electromagnetic spectrum is aclassification of different types ofradiation—energy that travels inwaves. Radio waves, microwaves, light,heat and X-rays are all forms ofelectromagnetic radiation. They all travel atthe speed of light, but have differentwavelengths—the distance between onewave crest and the next—and thereforedifferent frequencies—the number ofwaves per second. Different forms ofelectromagnetic radiation are groupedaccording to their wavelengths. Those withshorter wavelengths carry the most energy.Visible light ( 22) is the only part of thespectrum that we can see.

THE ELECTROMAGNETICSPECTRUM

IINNDDEEXX

30 31

AAabsolute scale 25absolute zero 24-25acceleration 16acid 14-15acoustics 20acrylic 9actinides 11, 12adhesion 8air resistance 16alkali 14-15alkali metals 11, 12alkaline earth metals 11, 12allotrope 8-9alloy 12-13alternating current 26aluminium (Al) 11, 12-13ammeter 26-27ampere (unit) 26amplitude 20arsenic (As) 13astatine (At) 8atom 6-10, 14-15, 17-19, 24,

26-27atomic number 6, 10

BBbase 14-15battery 12-13, 26-27bioluminescence 22bismuth (Bi) 13bond 8-9, 12, 18bromine (Br) 8bronze 12-13

CCcalcium (Ca) 9, 10, 12carbon (C) 8-9, 11, 12-13catalyst 14

Celsius scale 24centrifugal force 16-17centripetal force 16-17chemical energy 18-19, 26chemical properties 6-7,

10, 12, 15chemical reaction 8,

14-15, 22chemical symbols 8, 10chlorine (Cl) 8-9, 11 circuit 26-27circular motion 17coal 18cohesion 8cold 24colour 7, 13, 14, 22-23,

25, 29combustion 14compound 8-9, 13, 14concave lens 22-23concentration 14condensation 6conduction 24convection 24convection current 24convex lens 22-23copper (Cu) 8, 11, 12-13corrosion 14covalent bond 8-9crystal 8,15current electricity 26

DDdeceleration 16decibel (unit) 20-21density 6-7, 16diffraction 22diffusion 14direct current 26drag 16

EEecho 20-21, 28echolocation 20-21electric conductor 26electric current 14, 22,

26-27

electric insulator 26electrical charge 26, 28electricity 12, 18-19, 22,

26-27electrolysis 14electromagnet 26-27electromagnetic

radiation 28electromagnetic

spectrum 23, 28electromagnetism 26electron 6-7, 8-9, 12, 14,

26-27element 8-14energy 7, 14-15, 18-22,

24-26, 28-29evaporation 6

FFFahrenheit scale 25filter 14filtration 14fluid 6, 24fluorine (F) 8, 11focus 22-23forces 8, 16-19, 27fossil fuel 18freezing 6, 15, 25frequency 20, 28-29friction 16-17fuel 14, 18-19

GGgamma rays 28-29gas 6-7, 9, 16, 20-21, 24generator (dynamo) 26geothermal energy 18gold (Au) 11, 12-13gravity 16