Main How Things Work Encyclopedia
How Things Work EncyclopediaDK
Looking at the technology all around us-and then explaining how it works, the How Things Work Encyclopedia lifts the hood of a car engine, gets inside a TV set, and discovers the power of invisible microwaves. With close-ups, cutaways, and diagrams bringing the technology to life, and timelines illustrating the development of inventions, challenging curiosity quizzes and fascinating facts, the How Things Work Encyclopedia lets children really see and understand what's going on inside.
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But indian writer books is so small in number. Perhaps its for patent or copyright issue. But there are lots of books which released their patent... so please it would be helpful to us if those are uploaded
But indian writer books is so small in number. Perhaps its for patent or copyright issue. But there are lots of books which released their patent... so please it would be helpful to us if those are uploaded
23 November 2019 (17:15)
How Things Work Encyclopedia Machines+Biology Technology+Robots A first reference guide for inquisitive minds How Things Work Encyclopedia DK PUBLISHING LONDON, NEW YORK, MELBOURNE, MUNICH, and DELHI Senior Editors Carrie Love, Penny Smith Senior Designer Rachael Grady Design team Lauren Rosier, Pamela Shiels, Karen Hood, Hedi Gutt, Mary Sandberg, Sadie Thomas, Claire Patane, Laura Roberts-Jensen, and Poppy Joslin Editorial team Lorrie Mack, Elinor Greenwood, Alexander Cox, Fleur Star, Caroline Bingham, Wendy Horobin, and Ben Morgan Picture Researcher Myriam Megharbi Proofreader Anneka Wahlhaus Contents Consultant Roger Bridgman Publishing Manager Bridget Giles Art Director Rachael Foster Category Publisher Mary Ling Production Editor Sean Daly Production Controller Claire Pearson Jacket Designer Natalie Godwin Jacket Editor Mariza O’Keeffe US Editor Margaret Parrish First published in the United States in 2010 by DK Publishing 375 Hudson Street New York, New York 10014 Technology 4–5 6–7 8–9 10–11 12–13 Inventions Better by design Early inventions Modern technology Technology all around us Copyright © 2010 Dorling Kindersley Limited 10 11 12 13 14 10 9 8 7 6 5 4 3 2 1 175932—11/09 All rights reserved under International and Pan-American Copyright Conventions. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyright owner. Published in Great Britain by Dorling Kindersley Limited. A catalog record for this book is available from the Library of Congress. ISBN 978-0-7566-5835-9 Color reproduction by MDP, UK Printed and bound by Toppan, China Discover more at Hard at work 14–15 16–17 18–19 20–21 Simple machines Using levers Construction work Moving stuff Getting around 22–23 24–25 26–27 28–29 30–31 Getting around Wheels and axles Pedal power Holding the road Piston power www.dk.com 2 There is a question at the bottom of each page... Bits and bytes Engines of fire Race cars Up to speed Powering up Trains and tracks 94–95 96–97 98–99 100–101 102–103 104–105 106–107 108–109 110–111 112–113 114–115 Air and water Gases and liquids How fluids work Float that boat Floating balloons Roller coaster How do planes fly? Blastoff! In the future 116–119 Near future? 120–121 Not-so-near future What is energy? What is energy? It’s electric! The power of magnets Power plants Running out Renewable energy What’s cooking? Keeping cool Energy efficiency Light and sound Light and sound Now you see it... Light and bubbles Mirror,rorriM Lenses How light works Fireworks Measuring sound How ears hear Electric guitar 122–125 Glossary 126–127 Index 128 Picture credits About this book The pages of this book have special features that will show you how to get your hands on as much information as possible! Look for these: Gases and liquids Gases and liquids Curiosity quiz Gases and liquids Gas molecule Air and water are important examples of two types of substance—liquids and gases. They behave in different ways. Air is a gas. The molecules in a gas have a lot of energy and are always moving and colliding. This movement means they will fill up any container you put them in. If there is no container they will spread out as far as possible. Because there is a lot of empty space between gas molecules, gases can be squashed into small spaces. What’s a molecule? carbon dioxide 42 oxygen carbon oxygen oxygen Look through the “Gases and liquids” pages and see if you can identify the picture clues below. Liquid Liquids always take on the shape of their container. The molecules in a liquid are closer together than in a gas, but have less energy to move around. Special forces hold the liquid molecules together. It is very difficult to squash a liquid into a Water smaller space. molecule Gas Liquids and gases are made of molecules. Molecules are so tiny you can’t see them with the naked eye. Molecules are made of even tinier particles called atoms. Everything in the universe is made from atoms. Feel the breeze You can feel air molecules moving when the wind blows. Wind is simply air molecules being pushed by a force we call pressure. Scientists call water molecules H 2O (H stands for hydrogen and O stands for oxygen). Air molecules Air is made up of lots of different atoms bonded together in groups called molecules. The main molecules in air are nitrogen, oxygen, and carbon dioxide. hydrogen oxygen nitrogen Become an expert... on how ships float 46–47 on how airplanes fly 52–53 43 Bits and bytes Speech and music are turned into electrical signals by a microphone in a radio studio. Traditional radio sets pick up the radio waves and turn them back into speech and music. Digital transmission Digital radios also use a transmitter, but the waves they use are different from those of a traditional radio. What’s inside? The main parts of a radio are an antenna, a circuit board with a tuner and amplifier, and a loudspeaker. Baird’s televisor Images on the televisor were grainy. The mechanical system was soon replaced with a better quality electronic system. Digital radio When you listen to a digital radio there is little or no interference, such as hissing noises. Digital transmitters send out sound codes all mixed up together so that interference can’t affect them much and your radio will usually be able to understand them. Digital radios use codes made from lots of ones and zeros. They are transmitted over a large band of radio waves. First TV The scientific research for televisions began in the late 1800s. Baird’s televisor was the first ever TV to work. A rotating disk transformed light from a scene into lines forming a moving image. TV inventor John Logie Baird demonstrated the first television broadcasts in 1929. Transmission today Television stations transmit programs through electrical waves. Label Tucked behind the radio is the antenna. This picks up radio waves. 106 A neon lamp sent light into holes in a spinning disk. It’s hard to imagine life without radio or TV. We use both for information and entertainment. There are millions of programs, but how do they get to our radios and TVs? Inside the radio is a tuner and a computer chip that decodes the waves and converts them into sound. Television pictures are created by cameras in TV studios. The light coming through the spinning disk lit up a scene and made a moving image. The red light from the neon lamp made the image appear red. LCD TV LCD screens have been used since the 1970s in calculators and watches, but only recently for TVs. A modern LCD TV screen is made up of millions of tiny squares called pixels. If you look very closely at an LCD TV screen you can see the pixels. Programs can be sent up to satellites in space and then sent back to Earth. Satellite dishes can pick up the microwaves and send them to TVs along a cable. A TV turns the waves into the pictures and sound that make up a TV program. w ei Color squares Pixels contain blue, red, and green. When the pixels are turned on or off the colors merge, forming pictures. What does LCD stand for? Programs are sent out from the TV studio over wires or microwaves. r d o r w h at ? rd ei or wha t ? How do radios work? First called a wireless, the radio didn’t need wires to connect the transmitter and receiver. The radio transmitter sends out radio waves from the radio station. Every page is color-coded to show you which section it is in. Radio and TV Radio and TV Who invented radio? Guglielmo Marconi is credited with building the first radio system. In 1901, he transmitted radio signals across the Atlantic Ocean. The electrical signals from the speech and music travel through wires to a radio transmitter. The Curiosity quiz will get you searching through each section for the answers. Become an expert tells you where to look for more information on a subject. Water molecules Water molecules are made of two hydrogen atoms bonded to one oxygen atom. Water molecules are so sticky they clump together to form drops. What do we call materials in which the atoms cannot move? ... check here for the answer. 74–75 76–77 78–79 80–81 82–83 84–85 86–87 88–89 90–91 92–93 Reference section w 56–57 58–59 60–61 62–63 64–65 66–67 68–69 70–71 72–73 These buttons give extra weird and wonderful facts. There are roughly 1.5 billion television sets in the world. That’s one TV for every four people on the planet. Liquid-crystal display. 42–43 44–45 46–47 48–49 50–51 52–53 54–55 Bits and bytes Inside a laptop Binary code Sharing data Cell phones Digital photography Radio and TV Bar codes The Internet Search engines Robots Solids. 32–33 34–35 36–37 38–39 40–41 107 3 Technology Accidental ideas Inventions can happen by accident. Chemist John Wesley Hyatt was trying to find a material for billiard balls. He spilled a liquid that dried into a tough, flexible film—“celluloid” that was later used as camera film. Inventions Any new idea or product that has been created by a person can be called an invention. Inventions change the way people live their lives—they make things safer, easier, faster, or cheaper. Knowing your stuff Technology is the science of how things work. The inventors of these shoes knew that a coiled spring is a source of stored energy. They used this technology to make powered shoes. Expensive origins Some of the things in everyday use were developed for the space program. Smoke detectors, for example, were first used on Skylab. “Discovery consists of seeing what everyb ody h as seen and Telephone Refractometer Faraday’s induction ring Electric light bulb Cathode ray tube Wheel Eyeglasses 4 When was the first pair of shoes invented? Inventions I can find a use for that! Some inventions end up very different from what was planned. Scientist Dr. Spence Silver invented a glue that wasn’t sticky enough, so he thought it was useless. But his coworker Art Fry used it to stick bookmarks into his hymn book. The bookmarks wouldn’t fall out, but they could be moved around. And so the sticky note was born! Inventors Inventors are creative people. The Italian artist and scientist Leonardo da Vinci was an avid inventor. He designed hundreds of machines, including airplanes, pumps, and cannons, that were centuries ahead of their time. The first military helicopter, designed by Igor Sikorsky, took to the skies in the 1940s. How long does an invention take? An invention has to begin with an idea. It can sometimes take hundreds of years before the science, technology, or materials are advanced enough to make the idea work. The idea for a helicopter may have come from China as far back as 400 BCE. thinking wh else y d o b at no Wimhurst voltage generator Leo n des ardo ign da V yea f rs b or a h inci sk suc cess efore elicopt etched th e ful plan e first r 500 a e fl ight . has thoug ht.” Electric guitar Albert Szent-Györgyi Teamaker Microscope Camera 5 In 1500 BCE, people in Mesopotamia made the first leather shoe. Technology Better by design Anyone can be an inventor. Many successful inventions came from engineers who used their knowledge of materials (such as iron) to try new things. The Eddystone Lighthouse in Devon, England is also known as Smeaton’s Tower. New and improved Design engineer John Smeaton didn’t invent lighthouses, but he did design a new shape. The curved tower was wider at the base than the top and could stand up to storms. American inventor Thomas Edison patented an amazing 1,093 inventions. That was my idea! If someone thinks their idea is good, they can patent it. Patents are official documents that describe the idea and show who came up with it, so no one else can steal it and say it’s theirs. From that... Since the telephone was invented more than 130 years ago, people have changed the design to make it better. Early telephones were large and boxy. Making a call may have involved winding a handle or turning a dial. 6 When was the first telephone patented? John base Smeaton d on t his des he s ign ha an o ak t pe of ree. Better by design Meet an engineer Isambard Kingdom Brunel was a 19th century engineer who designed bridges, tunnels, ships, and even an entire railroad. He worked a lot with iron and knew it could be used in ways that had never been tried before. Will it sell? Brunel’s Royal Albert Railway Bridge was built in 1859. It’s the only one of its kind. Making a difference The way something looks can be just as important as how it works. The first colorful Apple iMac design made it stand out from other computers, so more people bought it. Even the best inventions can fail if people don’t want what you’ve made. Sinclair C5 Failure. Not many people wanted to buy a battery-powered tricycle. Lego Success! These plastic bricks are one of the bestselling toys in the world. Microwave oven Success! It has completely changed the way many people cook. Sneakers Success! Can you imagine playing sports in any other shoes? ... to this! Today’s cell phones are tiny by comparison, and you can do much more than just talk on them. You don’t even need to use your hands to call a friend. What will they think of next? 7 Alexander Graham Bell registered the patent in 1876. Technology Early inventions Some discoveries and inventions seem so basic it’s hard to imagine life without them. Yet someone had to be the first to create fire, wheels, shoes, paper... c. 7000 c. 2500 c. 3500 BCE The first wheel was made from solid wood. Experts think it was invented in Mesopotamia (modern-day Iraq). BCE Early welding involved hammering heated metal parts together until they joined. Now all kinds of metal objects could be made. 7000 BCE 2250 BCE c. 1700 c. 3000 BCE Reed boats were made from bundles of papyrus reeds by the ancient Egyptians, who used them for trade. c. 4000 8 BCE Spoked wheels were lighter and more useful than solid ones. Two-wheeled chariots could move very fast. BCE For the first time, people knew how to start a fire. Later, they would be using fire in metalwork to create tools. c. 6000 c. 2000 BCE Reed pens and brushes were used by the ancient Egyptians for drawing signs on papyrus (which was used before the invention of paper). BCE Evidence of early plumbing (drains and pipes) can be found among the ruins of the Palace of Knossos, on the island of Crete. c. 2500 BCE The first specially made mirror was made of polished bronze. Before then, people could see their reflections in water. BCE Wooden plows were pulled by animals to cut and turn soil for farming. What does the “c.” mean by the dates? Early inventions c. 500 c. 1000 BCE The earliest underfloor heating system is found in modern-day Alaska. The Romans invented their own system in Europe around 500 years later. c. 1000 BCE The Greek abacus was a table with counters that people used to make calculations. Today’s familiar abacus with rods and beads was invented in China almost 2,000 years later. c. 300 BCE The Chinese discovered that a free-moving magnet will point north—and so the compass was born. BCE The first magnets were simply lumps of magnetite, a naturally magnetic mineral. Modern magnets are made of steel. c. 50 1200 BCE c. 1500 c. 640 BCE Most early peoples wore sandals, but in Mesopotamia people crafted leather shoes to protect their feet. c. 1200 BCE Paper was invented in China more than 2,000 years ago, but the invention was kept a secret for 700 years. 100 BCE c. 20 BCE Before the first specially made coins, people paid for goods with beads, shells, tools, and even deer skins! c. 200 BCE The Archimedes screw is named after the Greek scientist Archimedes, who explained that water can travel upward along a turning screw. BCE Although glassmaking had been around for more than 2,000 years, the invention of glassblowing in Syria meant lots of new shapes could be made. BCE The first ships were built by Phoenicians and Greeks to carry large amounts of cargo for trade. 9 It stands for “circa,” which means “approximately.” Technology Modern technology Today, the phrase “modern technology” is usually used to mean computers. But a few hundred years ago, steam power and mechanical presses were new and exciting technology. 1455 Before Gutenberg’s movable type and printing press, books were copied by hand. Now they could be produced more quickly. 1400 1826 1565 The first photographic image was taken by Joseph Niépce in France. He had to leave his camera still for 8 hours! Historians think the first pencil was invented by Conrad Gesner in Germany. 1500 1608 In Holland, Hans Lipperhay invented the telescope— although some people think his children made one while playing! 1700 1600 1800 Important ideas Sometimes one invention leads to so many others, it changes the world. 1700s The first machines and factories used to massproduce goods led to the Industrial Revolution. 1800s For the first time, people could safely harness the power of electricity. 1970s The microprocessor made computers smaller and started the information age. 10 1829 1764 James Hargreaves’ spinning jenny made thread for cloth faster than ever before. 1769 James Watt’s improved steam engine was used to power all kinds of machines. Why was the printing press so important? Stephenson’s Rocket pulled the first successful steam train. It reached 12 mph (19 km/h). Modern technology 1903 The first powered flight took place in the US. The plane, the Wright Flyer, was made of wood and cloth. 1878 The first personal computers were large, chunky machines that had very little memory compared to today’s models. 1957 The light bulb was invented around the same time in two different countries—by Thomas Edison in the US and Joseph Swan in Britain. 1876 1977 The Soviet Union’s Sputnik 1 was the first man-made space satellite. Alexander Graham Bell got the first patent for a telephone, although others nearly beat him to it. 1982 The first compact discs were jointly produced by electronics companies Philips and Sony Corporation. 1926 The Televisor was the first kind of television. It was replaced by electronic television in 1936. 2000 1900 WWW 1885 1990 Karl Benz made the first gasolinepowered car in Germany. By 1896, there were 130 Benz cars on the roads. The World Wide Web meant anyone could get information from across the world over the Internet. 1895 German scientist Wilhelm Röntgen accidentally discovered X-rays as a way of seeing through tissue. 1938 Laszlo and Georg Biró’s ballpoint pen had fast-drying ink and didn’t need to be refilled very often. 1979 This year saw the first public cellphone system, in Japan. 1998 The first handheld E-book reader could store 10 books or 4,000 pages. 11 More books were made, so knowledge and ideas could spread more easily. Technology Technology all around us Which te c ogy is yo l o u hn Become an expert... on space travel, pages 54–55 on robots, pages 114–115 avorite? rf The use of science to provide new and better machines and ways of doing things is called technology. Every day, you use technology in one of its many different forms. Here are a few of them. Mechanical Mechanical technology is the design, production, and use of machines like wind-up clocks and other appliances that do not use electrical, electronic, or computer technology. Chemical technology is used to make plastics and refine gasoline. Chemical When the science of chemistry is used to turn raw materials into more useful things like plastics, cosmetics, or drugs, this is called chemical technology. Electrical Technology that deals with electrical circuits and equipment is known as electrical technology. It is commonly used in the design and construction of machines and power grids. 12 How does nanotechnology get its name? Digital Technology all around us In digital technology, information is recorded using combinations of 0 and 1 to represent words and pictures. This system allows huge amounts of data to be squeezed into tiny spaces. Biotechnology This term refers to technology that is based on biology—the study of living things. Biotechnology is commonly used in agriculture and food production. Genetic engineering is biotechnology. Medical Anything (like a tool, machine, process, or substance) that is used to diagnose, observe, treat, cure, or prevent people’s illnesses or injuries comes under the heading of medical technology. Information The study, design, and use of electronic information systems is known as information technology. The term covers machines like computers (hardware) and the programs they run (software). When you log on to a computer, you use information technology. Modern science can create materials and simple machines much too small for you to see under a normal microscope. This nanotechnology is used in products like special sunscreens and textiles. Antibacterial bandage Sunscreen Nanotechnology NO NA N SU SPF Odorresistant socks 13 “Nano” is Greek and originally meant “dwarf.” Hard at work Simple machines It’s hard to hit a nail into wood with your hand, but much easier with a hammer. Tools such as this are called simple machines. They help people work faster and better. A small movement from your hand travels down the handle to the head. As the head moves, it stores energy. When the head hits the nail, the stored energy is released as a large force that can split wood. Class 1 lever Levers consist of a solid part that turns around a fixed point, called the fulcrum. In class 1 levers, the fulcrum is in the middle. The force you apply at one end is magnified at the other end. Magnified force Solid part Force you apply Loa d Fulcrum Class 2 lever In class 2 levers, the fulcrum is at one end and your hands apply a force at the other end. This creates a magnified force in the middle. Magnified force Force you apply Loa d Feel the force Tools, levers, and pulleys are all simple machines. They increase the size of the force you apply, so you can perform a job with less effort. When you use a hammer, you only need to move the handle a small way to give the head enough energy to push the nail through wood. Levers move loads Fulcrum Class 3 lever Class 3 levers reduce the force you apply. They are used in tweezers and other tools that pick up small, delicate objects. Levers are simple machines that work by magnifying or reducing a force. A wheelbarrow is a kind of lever. It magnifies the lifting force from your arms so that you can lift and move much heavier loads. There are three different types of lever: class 1, class 2, and class 3. 14 What is a force? Reduced force Force you apply Fulcrum Loa d Simple machines Curiosity quiz Pulley power Fulcrum A pair of scissors is made of two class 1 levers. You apply force with your fingers, and this force is magnified at the blades, giving them the power they need to cut through paper or other materials. Pulleys are used to lift heavy loads. A pulley is a length of rope wrapped around a wheel. Adding more wheels to the pulley system creates more lifting force—but you have to pull the rope farther to lift the load. Look through the “Hard at work” pages and see if you can identify the picture clues below. Wheel Edge-on view of a pulley wheel Pulling on the end of the rope will shorten the rope that’s wrapped around the pulley and lift the weight. Fulcrum A wheelbarrow is a class 2 lever. It magnifies the weak force from your arms to pick up the heavy load. Rope Rope Fulcrum The rope sits in a groove in the wheel so it won’t slip out. Become an expert... The fulcrum in this pair of chopsticks is where they rest in the girl’s hand. Her fingers apply the force that opens and closes the chopsticks to pick up food. on cranes, pages 18–19 on conveyors, pages 20–21 15 The power that makes things move. Simply put—a push or a pull. Hard at work Using levers Levers at home These are all compound levers—tools made up of more than one lever. Every time you open a door, ride a bike, or even bend your arm, you are using levers. Many of the objects we use every day depend on leverage to magnify forces and make tasks easier. Nutcrackers are a pair of class 2 levers that are joined at the fulcrum. Tweezers are made up of two class 3 levers. They reduce the force you apply. Magnifying forces Scissors are class 1 levers. The strongest cutting force is nearest the hinge. The amount by which a lever magnifies a force depends on how far the force you apply and the force the lever produces are from the fulcrum. Force you apply Force you apply Force from lever Force from lever Fulcrum If the force you apply is the same distance from the fulcrum as the force the lever produces, the two forces are equal. Crowbar One of the simplest kinds of lever is the crowbar, which is a class 1 lever. You use a crowbar to prize very heavy objects off the ground. The longer the crowbar is, the more the force is magnified at the other end. However, you have to move the long end of the crowbar much farther than the short end will move. 16 Force you apply Force from lever Fulcrum Fulcrum If the force you apply is twice as far from the fulcrum as the force the lever produces, the lever doubles the force. If the force you apply is three times as far from the fulcrum as the force the lever produces, the lever triples the force. Force you apply Force from lever Load Fulcrum Moving the crowbar a long way provides enough force to lift the heavy rock a short distance. Can you name other compound levers found around the home? Force from lever Using levers Human body Your arms and legs are levers. When you stand on tiptoes, your lower leg works as a class 2 lever. The powerful calf muscle pulls up your heel, lifting your body weight (the load), while your toes form the fulcrum. Force you apply Load Fulcrum Fishing rod When you use a fishing rod to cast a line, the rod works as a class 3 lever. Your hand applies a powerful force near the base of the rod to create a smaller force at the tip of the rod. Although the force is weaker, the tip moves much farther and faster than your hands, magnifying the speed. Force you apply Load The rod also works as a class 3 lever when you haul in a fish. Fulcrum Seesaw A seesaw is a class 1 lever. You use the force of your body weight to move the seesaw. If two people of equal weight sit at equal distance from the fulcrum, their weight will balance. But if one of them sits farther from the fulcrum, their weight is magnified and the seesaw tips over. A small child could balance the weight of an elephant by sitting far enough from the fulcrum. Force you apply Fulcrum 17 Pliers are class 1 compound levers. Tongs are class 3 compound levers. Hard at work The long arm of the crane is called the jib. Construction work Digging dirt, lifting loads— there’s lots of heavy work to do on a construction site, and lots of large machinery to do it. Yet most of these machines use fairly simple science to do their jobs. The crane’s operator sits inside a small cab. A wheeled cart runs along tracks in the jib to move the load outward. A slew ring allows the top of the crane to turn around in a circle. Tower Why don’t cranes fall over? Tower cranes pick up and move the massive blocks of concrete and steel used to construct big buildings. A huge concrete “counterweight” on the rear arm of the crane balances the load carried by the main arm (jib). This stops the crane from toppling over. Hydraulic ram Large weights must be lifted close to the main tower, while small weights can be picked up at the end of the jib. Jib 20 tons Counterweight Tower 20 tons 10 tons 7 tons Each of these loads is balanced, but the crane could not pick up all three at once. 18 What is a crane’s first job when it arrives at a construction site? Pulleys in action Cranes lift objects with a hook and pulley. A steel cable is looped around pulley wheels on the hook and jib and is wound in by a motor in the crane’s rear arm. Each loop of cable magnifies the crane’s lifting force. Diggers Diggers use a set of connected levers to scoop earth out of the ground. The levers are joined like the parts of a human arm, the bucket forming the “hand.” They are moved by hydraulic rams— metal tubes that extend as oil is pumped into them. Construction work Hydraulic cranes Mobile cranes, such as those on fire engines, are hydraulic cranes. Like diggers, they use hydraulic rams to transmit the force needed to lift loads. By varying the size of the metal tubes in the rams, the hydraulic system creates huge lifting forces—enough to raise bridges, trains, and even entire buildings. Hydraulic ram Like pulleys and levers, hydraulic rams can magnify forces. Boom When the bucket is pushed inward, its sharp teeth dig into the ground to scoop out earth. Slew ring Bucket The slew ring at the base of the arm allows the arm to rotate (turn around). 19 It builds itself, adding one section at a time to its tower. Hard at work Moving stuff From airports and factories to stores and offices, conveyors are used in all kinds of places to make it easier to move loads from one point to another. A gravity conveyor seen from above. Move along The simplest type of conveyor is a gravity conveyor. This is made up of lots of rollers or wheels in a frame. As each roller or wheel turns, the load gets shifted along to the next. Luggage and other cargo are moved on conveyors behind the scenes at an airport. The drive pulley, connected to an electric motor, does the work. Up, down, and sideways Belt conveyors can move loads up, down, and sideways. The load sits on a belt that turns around rollers called pulleys. The drive pulley is connected to a motor, which makes it rotate. Chain 20 Sprocket When was the first escalator used? The motor is hidden away under the bed to take up less room. The motor turns fast—1,750 times a minute! A speed reducer is added so the drive pulley will not turn so quickly. Moving stuff How to drive The parts that make a conveyor belt turn are called the conveyor drive. Sprockets and chains are part of this. The chain sits in the gaps between the sprocket’s teeth so it doesn’t slip. When the motor sprocket turns, the chain moves and turns the drive pulley sprocket. Sprocket Going up! It’s not just boxes that are moved around on conveyors—people are, too. Escalators are moving staircases with each separate step connected to a conveyor belt. Even when the steps turn around the belt, they always The steps are stay level. connected to two belts. Wheels near the top of each step follow the drive belt, which is turned by the motor. Electric motor An escalator can carry more than 10,000 people in an hour. The handrail is also turned by the motor so you can hold on safely. Drive pulley Inner rail The steps flatten out at the top and bottom of the escalator so you don’t trip getting on and off. Sprocket Drive belt The belt loops all the way around the bed and pulleys. Bed To stop the belt from sagging underneath, it might be tucked around small rollers called return idlers. Guide wheels at the bottom of each step roll along the inner rail to keep the steps stable. Tail pulley The tail pulley turns by itself. 21 The first working model was made in the US in 1895—as a fairground ride! Getting around Getting around = Energy We can all use our legs for getting around, but they’re a bit slow and won’t take us far without making us tired. What we need is something that can get us from A to B fast—a vehicle of some kind. Energy sources To move or do any kind of work you need energy. We get energy from our food; vehicles use fuel or electricity. But what does it take to get a car racing along a road? Energy-rich oil One of the best sources of energy is oil. When oil is burned it releases lots of energy. Types of fuel Vehicles can get their energy from many different types of fuel: P Gasoline is made from oil. Most cars run on gas burned in the engine. D Diesel is also made from oil. It produces more energy than gasoline. Electricity can be used to power some cars but is mainly used by trains. Solar energy comes from the Sun. It can be stored for use by cars. 22 What moves faster than anything else in the universe? Force Movement Getting going On the move Once you have enough energy, you can use it to create forces that will help you move. Forces are simply pushes or pulls. When you apply a force, things move. When you don’t, they stay still. The greater the force, the faster something goes. Getting around Curiosity quiz Look through the “Getting around” pages and see if you can identify the picture clues below. PUSH Speeding up Speed is the key to getting somewhere fast. To increase your speed you need to be able to provide a lot of power quickly. A good engine and the right kind of fuel help. Wheels turn by using opposing forces. As the tire pushes back against the road, the road pushes the wheel forward. Friction Friction is a force that stops things from moving by pulling them in the other direction. Without its gripping action, you couldn’t walk or drive anywhere. Brakes work by pushing pads or disks against the wheels. Slowing down If you push against a moving object it will slow down and eventually stop. This is called braking. Light. PULL Become an expert... on how bicycles work, 26–27 on car engines, 32–33 23 Getting around Wheels and axles An axle is a simple rod that connects two wheels. For nearly 6,000 years, the wheel and axle have made it easy to move objects. Friction Friction is the force created when two surfaces touch. As you slide an object along, you create a lot of friction. When you roll it on wheels, you create less. Fixed axle A fixed axle can be found on simple carts. The axle is attached to the cart and the wheels turn independently, Wheel allowing the cart to move. The axle does not turn Axle Pushing this box is hard work. The large area of the box in contact with the floor creates sliding friction. Some friction is created as the wheel turns against the axle. A lot of friction Put the box on wheels and it gets easier. The wheels turn and change sliding friction into the less forceful rolling friction Carts have big wheels so they don’t get stuck on bumpy roads. The large wheel gives it extra grip. Less friction History wheels Historians believe the very first wheels were used 8,000 years ago by potters to make pots. Then the wheel was used to help move and transport objects. 24 The first use of wheels and an axle was on horse-drawn chariots around 3500 BCE. What is the largest wheel in the world? Bicycles, which allow us to create our own power, have been popular for over 100 years. Outer rim Spoke support The little rods that connect the outer rim to the inner hub of the wheel are called spokes. They make the wheel lighter but are strong enough to take the weight. They also spread the weight evenly, and transfer power from the axle. Wheels don’t just move you or your belongings. They have a diverse range of uses: Hub A steering wheel is the fifth wheel on a car and helps guide it. Rolling axle Modern cars and vehicles use a rolling axle system. The axle is connected to the engine and helps turn the wheels. The wheels turn with the axle Wheel Spoke Wheels and axles Other wheels Gears Axle Gears use interlocking “teeth” to transfer movement and power. Pulleys and levers use wheels to pick up and move heavy objects. The engine turns a rod known as the driveshaft. This uses gears to transfer the engine’s power into the axle. Waterwheels create mechanical energy when a river’s current turns them. Driveshaft The turning force created by the axle moves the wheel. rd wei or what ? The tweel is a brand new car wheel that doesn’t need a tire. Instead, it uses flexible spokes, which bend with the bumps in the road. The tweel will never get a flat like a tire. In “two-wheel drive” cars, one axle powers just two wheels. “Four-wheel drive” cars are powered by both axles. With the invention of the engine, bigger vehicles needed bigger wheels to help move heavy cargo. After a few early designs, the automobile was built and its wheels were covered with air-filled rubber tires. The modern-day wheel is a hi-tech device. Race cars use special wheels for different racing conditions. 25 The observation wheel The Singapore Flyer stands 541 ft (165 m) high. Getting around The history of bikes The dandy horse (1817) The first bikes had no pedals at all. Riders had to push them along with their feet until they came to a downhill slope. The velocipede (1863) The pedals on this bike were fixed to its wheels, and it had no gears. This meant the wheel turned once for every turn of the pedal. It took a huge effort to travel fast. Pedal power A bicycle is a lean, mean travel machine. Bikes are so efficient, they can turn 90 percent of the energy you put into pedaling into forward motion. Get in gear Bikes can have up to 30 gears. They are cogs, or wheels with teeth, that are linked by a chain. Using different gears makes pedaling easier or faster. When a small gear at the front wheel is connected to a large gear at the back, the bike is in low gear. This turns the wheel slowly but forcefully, so is ideal for traveling uphill. The penny farthing (1872) These bikes got around the problem of fixed pedals by having a huge front wheel. They were faster but also dangerous— it was a long fall down from the seat. The safety bicycle (around 1884) This was the original name for a bicycle with gears—the same basic design that is used today. When a large gear at the front wheel is connected to a small gear at the back, the bike is in high gear. The wheel will turn several times for each rotation of the pedals. This is ideal for speeding along a flat surface or racing downhill. 26 The main picture shows a BMX bike. What does BMX stand for? Pedal power Handlebars These are used to control the front wheel. Moving the handlebars lets you change direction and also helps you keep your balance as you cycle along. Handlebars are levers, and the longer they are, the easier they are to turn. Brakes When you squeeze the brake lever on the handlebars, it pulls a cable that’s connected to brake shoes on either side of the wheel. The rubber shoes grip onto the wheel like a clamp. This creates friction against the wheel, slowing it down. Bike types Utility bikes are used for everyday cycling. A chain guard stops the oily chain from getting your clothes dirty, and bags can sit safely in the front basket. Frame Most modern bikes have a “diamond” frame—a shape made up of two triangles of hollow steel, which is light but strong. Mountain bikes have a strong frame and wide tires for extra grip on rough ground. Pedals These turn the up-and-down motion of your legs into the circular movement of the wheels. Tires Patterns called treads on the tires increase friction between the bike wheel and the road surface, so that the bike is easy to control and keeps a good grip, even in rainy conditions. Wheels The spokes near the top of each wheel carry the weight of the bike and rider. ir e w d or what ? The world’s longest true bicycle (one with just two wheels) was built in The Netherlands in 2002. It was 92¼ ft (28.1 m) long! Track-racing bikes are designed for speed. The rider must bend low to hold the handlebars, making a streamlined shape. These bikes have no brakes! Recumbent bikes have frames that make the rider lean back in their seat. Some have covers, too. They can be tricky to ride, but can go very fast. 27 Bicycle Motocross, a sport based on motocycle racing (”motocross”). Getting around Holding the road Why do trucks and tractors need such big wheels? It’s to help them get a grip on slippery surfaces and move easily while pulling loads. Sticking to the surface Heavy vehicles need big tires to help spread the weight of the truck and its load. It is the tires that move the vehicle, using friction. As the tires press down and backward on the road, the road pushes the vehicle forward. Losing your grip This car’s wheels can’t get enough grip to move. Mud is wet and slimy and does not have any snags and bumps to provide friction. The car’s wheels are too small and smooth to provide enough surface area to reduce the pressure of the heavy weight of the car on the ground. 28 Tractors overcome this problem by having wide tires with deep treads that provide a better grip. Tractor Car How big is the world’s largest tire? The sloping ridges push mud out from under the tire. Holding the road Monster trucks What do you get if you put the body of a pickup truck on a bus axle? The answer is a monster truck. Add some tractor wheels and a good suspension system and you can bounce over anything. Smoothing out the bumps When you hit a bump in the road your wheels move up and down. The suspension system is designed to absorb the impact through the tires, springs, and shock absorbers. Inside the shock absorber is a piston that pushes against a gas. The gas slows the piston down and turns its energy into heat. Spring Crosssection Shock absorber Tire Tires Tires are left slightly soft so they can squash over small bumps without moving up and down. Springs There is a spring around each shock absorber that reduces the impact by squeezing and stretching. Shock absorbers These are pumps filled with gas that absorb the energy of the wheel hitting the ground. 29 It measures 13 ft (4 m) across and weighs 8 tons (7.3 metric tons). Getting around Piston power Many forms of transportation use wheels, which push against the ground and use friction to move. But what makes the wheels turn? Up and down, around and around To ride a bike, you move your legs up and down on the pedals. The pedals turn cranks around and around to turn the wheels. A car’s wheels move in a similar way. Cylinder Gear Crank Pistons Pedal Crankshaft Cranks Rear-wheel drive A bike’s cranks turn a chain that is connected to the back wheel, so when you pedal, you are actually only powering one wheel. Many bikes have gears to make pedaling easier. Types of engine Different vehicles have different numbers of cylinders. Generally, the larger the vehicle, the more they have. 30 A lawnmower has only one cylinder (so only one piston going up and down to turn the wheels). A car has pistons rather than pedals to move the cranks. This motorcycle has two large cylinders. Their slow up-and-down motion gives the Harley its distinctive sound. Thump! Thump! Lawnmower What is a “four-wheel drive” car? Harley Davidson Piston power Secret cylinders d by its back w forwar heel s. is There is a row of metal pistons hidden deep in a car’s engine. The pistons pump up and en v i down, just like your dr feet on a bike. , 4 et h lik Start at 1 to see how the pistons power the wheels. ik e b e i Th , r a sc 2 Axle Axle Car pistons are also attached to levers called cranks. These turn the crankshaft. Pistons The pistons pump up and down like legs. 1 Driveshaft Gearbox Rotation relay The pistons are connected to the crankshaft. The crankshaft is connected to the driveshaft. The driveshaft is connected to the axles, and the wheels go around and around... Formula 1 car This huge cargo ship is five stories high and weighs over 2,750 tons (2,500 metric tons). It has 14 cylinders, each one bigger than a person. 3 The crankshaft turns the driveshaft through the gearbox. Crankshaft A Formula 1 race car needs an extremely fast and powerful engine. It has 8 cylinders. The driveshaft turns the wheel axles and the wheel axles turn the wheels. Become an expert... on internal combustion engines, 32–33 on racing cars, 34–35 Emma Maersk 31 When the pistons are connected to all four wheels of the car so they all turn. Getting around Engines of fire Cars, and other vehicles, must burn fuel to release the energy needed to move. This happens inside an “internal combustion engine”—an engine that is powered by lots of little fires. Recipe for fire: Fuel + oxygen + a spark = fire. What makes it burn? Fuels such as gasoline and diesel burn easily. All they need are a spark and oxygen. Oxygen is found in the air. Exploding with power At normal speed, a car’s engine lights around 50 little fires every second. The fires make pistons shoot up and down, with four “strokes” for every fire—suck, squeeze, bang, and blow. Air is sucked in through this valve. 2 1 Suck The piston moves down, sucking in air through a valve. A tiny squirt of gasoline is injected into the air at the same time. Crankshaft turns 32 Air and gas Squeeze The valve that lets in the air at the top closes, trapping everything inside. The piston moves up, squeezing the air and gasoline tightly together. The crankshaft turns around, pushing the piston up. What actually is fire? Engines of fire The cylinders The combustion (burning) happens in an engine’s cylinders. The energy let off by each tiny explosion is directed to the pistons and causes them to move up and down. This drives the crankshaft around and around, turning the wheels (see pages 30-31). The pistons are found deep in the engine, fitting snugly into hollow cylinders. Fuel burns inside the cylinders. These valves let air and gasoline in. Cylinder Piston Crankshaft 3 Bang The spark plug releases a spark into the mix— BANG! When the piston reaches the top, a carefully timed spark sets fire to the gasoline. The gasoline burns very quickly, forcing the piston back down. 4 Blow Finally, the piston moves back up and pushes the burned gases out of the outlet valve. These gases leave the car through the exhaust. Waste gases blow out of this valve, on the way to the exhaust pipe. 33 It’s a high-speed chemical reaction that produces heat and light. Getting around Race cars Formula 1 cars are like normal cars in many ways. They have gas engines, gears, and steering wheels. However, they are built with only one thing in mind, and that’s WINNING RACES! A technical masterpiece Every bit of a Formula 1 (F1) car is light and very strong. At its peak speed of 225 mph (360 kph) air flows over it with the force of a tornado, so it is as low and streamlined as possible. Pit-stop pressure At pit stops, a driver refuels and gets new tires. This is all done in about 30 seconds. That’s about the same amount of time as it takes to read this paragraph! The car’s spoilers create a downward force that stops the car from taking off at high speed. Even the driver’s helmet is part of the streamlining. The blue arrows show how air flows over the car as it races. 34 What is the minimum weight of a Formula 1 race car? Race cars G-force The car accelerates A Formula 1 driver is shoved around violently inside his car as it twists around the track. A pushing force called g-force, which can be up to six times more powerful than gravity, shoves him backward, forward, and sideways as he races. You see g-force at work in a normal car by watching water sloshing in a cup. Water spills out backward. The car brakes Water spills out forward. The car turns right This driver’s helmet is attached to his seat to stop his head from swinging around because of g-force. Water spills out to the left. The car turns left Inertia G-force is caused by inertia. The law of inertia says that moving objects try to travel straight at a constant speed. When a car stops abruptly, your body tries to keep going forward. Water spills out to the right. Label Steering wheel Because an F1 driver is concentrating so hard on winning a race and because the space he is in is so tight, all the controls for the car are on hand on his steering wheel. He has just two foot pedals—the brake and the accelerator. These buttons fulfill all the driver’s needs, from traction control to drinks dispenser—drinks are pumped by tube straight into the driver’s mouth. He doesn’t worry about spilling HIS drink! 35 Including the driver, the minimum weight is 1,300 lb (600 kg). Getting around 80 90 100 70 110 0 6 120 50 130 40 140 H 150 MP 30 20 10 Up to speed Once you’re on the move, you naturally want to go as fast as you can. But what makes sports cars really fast and tankers really slow? Speed isn’t just about raw power—other factors are at work. Speed, velocity, and acceleration Acceleration isn’t just speeding up. Scientists also use it to describe all changes in velocity, like slowing down and even changing direction. You measure speed by dividing the distance traveled by the time it takes. Speed is not the same as velocity, which is a measure of how fast you are going in a particular direction. You feel acceleration when you pedal your bike really hard. Acceleration measures how quickly your velocity is changing. Horsepower? Engine power is still measured using a very old unit—the horsepower. It is based on how many horses would be needed to provide the same amount of pulling power. An average mid-sized car is equivalent to 135 horses. 36 How fast are electric cars? Up to speed Pulling power If you have a powerful engine you can accelerate very fast, which is why a sports car will always beat a lawnmower. But if you give a ride to an elephant your acceleration will suffer. That is because it takes more force to speed up heavy objects. Milk tanker vs. Ariel Atom Both have a 300 horsepower engine. A full tanker can weigh as much as 110 tons (100 metric tons). The Atom weighs half a ton. Even though they have the same pulling power, the weight of the milk means the tanker takes 35 seconds to accelerate from 0 to 60 mph (97 km/h). The Atom can do it in 2.7 seconds, making it one of the fastest accelerating road cars in the world. Not such a drag Nothing accelerates as fast as a dragster—not even the space shuttle. Dragsters can go from 0 to 330 mph (530 km/h) in less than 4.5 seconds. They use nitromethane as fuel, which provides twice as much power as gas. The rear wheels have to be really big to transfer the high power made by the enigne. Superfast cars If you want to go really fast and break records, then there’s only one solution—strap a jet engine or two to your chassis. Jet engines don’t use pistons. Instead, they suck air through the front of the engine, use it to burn fuel, and then blast the hot exhaust out of the back. This pushes the car forward at speeds of up to 760 mph (1,230 km/h). 37 The Tesla Roadster can reach speeds of 130 mph (210 km/h). Getting around Powering up Most cars are powered by gasoline engines, but there are many other ways to power a vehicle. In the future, renewable forms of power that don’t depend on fossil fuels such as gasoline will become more important. Solar car The solar panels on a solar car use sunlight to generate electricity. The electricity powers an Solar cars work best electric motor that turns the in very sunny places. They tend to be flat wheels. Solar cars are not and very wide or long to create room for the powerful and so must be large solar panels on the roof. very light and streamlined. Electric car Electric cars carry energy in rechargeable batteries instead of gas. The battery releases energy as electricity, which drives a motor that turns the wheels. One problem is that recharging can take hours. The curved front and flat body make the car streamlined, which reduces its energy needs. Electric motor A solar panel is made of lots of separate units called cells. 38 When did the hybrid car go on sale? Powering up Biofuel Many ordinary cars can run on biofuels—fuels made from plants. Biodiesel, for instance, is a biofuel made from vegetable oil. In some countries, including Brazil and the US, gasoline is diluted with alcohol made from corn or sugarcane. Using biofuels reduces pollution, but biofuels can harm the environment because growing them uses vast areas of land. Corn is mixed with water and left to ferment. The sugar turns to alcohol, which is added to gas. Hydrogen power Hydrogen-powered vehicles use liquid hydrogen as a fuel instead of gasoline. The hydrogen flows into a device called a fuel cell, which combines hydrogen with oxygen from the air to make water and electricity. The electricity drives the car’s motor and wheels, just as in an electric car. Fuel tank Battery Hybrid car Gas engine. In some hybrids, the engine drives the wheels, but in others it merely charges the batteries. Hybrid cars Hybrid cars are powered by a combination of gas and electricity from batteries. When the car stops, the brakes capture energy and use it to charge the batteries. A computer switches between the two forms of power to make the best use of energy. Electric motor Air car The air car works a bit like a balloon. High pressure air is stored in an air tank and released through a valve when the driver pushes the accelerator. The jet of air turns the engine. 39 In 1917. Getting around Trains and tracks Most countries have a railroad system where trains travel on steel tracks. Trains are often powered by electricity that runs through rails or cables. This train’s cars tilt to help it travel around corners at high speed. Diesel electric Some electric trains run on diesel fuel. The diesel is burned to make electricity. This electricity powers the motors that make the wheels turn and the train move. Engine and generator unit Electric third rail Other trains use an electrified third rail. The train picks up the electricity using a device called a shoe. Most freight trains are powered by diesel electrics. Train wheel Shoe Electrified rails are dangerous! You can be killed if you step on the third rail. Overhead cables There are trains that take electricity from overhead cables using a metal arm. The cables carry high-voltage electricity—around 25,000 volts. The train’s metal arm is called a pantograph. 40 What color lights do signals use? Trains and tracks Train travel Signals Signals tell the train driver when it is safe to move forward, when to proceed carefully to the next section of track, and when to stop. You need wheels Trains have metal wheels with a rim, called a flange, on the inside to stop them slipping off the track. Usually the flanges never touch the rails, but if they do you hear a squealing noise. Trains are the most efficient way to move people and goods. Freight trains carry goods and can be more than 4 miles (7 km) long. Bullet trains in Japan provided the world’s first high-speed rail service. Wheels are slightly cone shaped. Flanges The French TGV is the fastest train ever built. It can go at 322 mph (515 km/h). Rails Eurostar travels between England and France through the Channel Tunnel. Wheel centrally placed on rail. The Trans-Siberian Express makes the longest trip— 5,857 miles (9,297 km). Straight track On the tracks Railroad tracks guide trains from station to station. They are made of steel and usually welded together to give a smooth ride. Some rails are moveable. These are called points. They help the train switch from one track to another. The Qinghai–Tibet railroad is the highest anywhere—passengers need to carry oxygen. B A Points C The rail sits in metal tie plates that are bolted onto the ties. The rail is joined to ties, which keep the two rails the right distance apart. The track is laid on ballast made from broken stone. Brakes Metal wheels can slip when the train engineer brakes on icy rails. So a small amount of sand is dropped in front of them to help them grip the rail. Red, yellow, and green, like traffic lights. Points 41 Gases and liquids Gases and liquids Gas molecule Air and water are important examples of two types of substance—liquids and gases. They behave in different ways. Gas Air is a gas. The molecules in a gas have a lot of energy and are always moving and colliding. This movement means they will fill up any container you put them in. If there is no container they will spread out as far as possible. Because there is a lot of empty space between gas molecules, gases can be squashed into small spaces. What’s a molecule? Liquids and gases are made of molecules. Molecules are so tiny you can’t see them with the naked eye. Molecules are made of even tinier particles called atoms. Everything in the universe is made from atoms. carbon dioxide Feel the breeze You can feel air molecules moving when the wind blows. Wind is simply air molecules being pushed by a force we call pressure. 42 oxygen oxygen carbon oxygen Air molecules Air is made up of lots of different atoms bonded together in groups called molecules. The main molecules in air are nitrogen, oxygen, and carbon dioxide. nitrogen What do we call materials in which the atoms cannot move? Gases and liquids Curiosity quiz Scientists call water molecules H2O (H stands for hydrogen and O stands for oxygen). Look through the “Gases and liquids” pages and see if you can identify the picture clues below. Liquid Liquids always take on the shape of their container. The molecules in a liquid are closer together than in a gas, but have less energy to move around. Special forces hold the liquid molecules together. It is very difficult to squash a liquid into a Water smaller space. molecule oxygen Solids. hydrogen Water molecules Water molecules are made of two hydrogen atoms bonded to one oxygen atom. Water molecules are so sticky they clump together to form drops. Become an expert... on how ships float, 46–47 on how airplanes fly, 52–53 43 Gases and liquids How fluids work Gases (such as air) and liquids (such as water) are known as “fluids.” This is because they move in a similar way and can flow around corners and fill containers. Fluid motion Fluids flow smoothly over curved (streamlined) objects. They do not flow smoothly over shapes that have corners and bumps. These slow fluids down, causing a force called drag. Smooth sides mean a fluid only has to travel a short distance around an object. This produces little or no drag. Smooth shape Fluid flow Block shapes with flat edges split the fluid’s flow into different streams. Some pass over an object. Some pass around it. Others twist and turn back, creating areas of drag known as eddies. Fluid flow Sir Isaac Newton discovered gravity when an apple fell from a tree. 44 Streamlined car A car is designed to be as streamlined as possible, so air can pass over it smoothly. Block shape Eddy Gravity and weight Gravity is the force that keeps you stuck to the ground. It also keeps the Moon in orbit around the Earth, and keeps the Earth traveling around the Sun. Gravity gives everything weight. Without it you would simply float away as if you were in space. What is more dense—water or air? How fluids work How dense? The weight of an object also depends on its mass—the amount of tiny particles (called atoms) it contains. Some substances pack more atoms into a space than others. The more closely packed the atoms are, the more dense the substance is. All substances have different densities. A kilogram (2 1/5 lb) of bricks weighs the same as a kilogram of oranges, but the oranges take up more space. Because the mass of the bricks is packed into a smaller space, we say the bricks have a higher density than the oranges. Moving through fluids When objects move through a fluid they either float or sink, depending on their density. An object will float in air if it is less dense than air. An object will float in water if it is less dense than water. The gas inside the balloon is lighter than the air around it, so it rises slowly. Boats float because they are mainly filled with air, which is less dense than water. An object will sink in air if it is more dense than air. An object will sink in water if it is more dense than water. Apples are denser than air so they drop from trees. Brick molecules are very close together, making bricks dense, so they sink. 45 Water is 1,000 times more dense than air. Gases and liquids Float that boat How do ships float, and why do they sometimes sink? It’s all about buoyancy. Setting sail A ship is very heavy, especially when it’s loaded with crew, passengers, and cargo. But the ship still floats because as it pushes down, it displaces water, and the displaced water pushes upward. If the ship weighs less than the displaced water, it will float. (See page 45.) Floating beach ball Buoyancy When an object weighs less than the amount of water it displaces, it floats (or is “buoyant”). If it weighs more, it sinks. The weight of the ship is spread out across the hull. Gravity Balancing act While buoyancy pushes the boat upward, gravity pulls it downward. These two forces balance each other out, so a ship can float on the water. 46 Buoyancy What’s the longest ship in the world? Sinking golf ball If one compartment starts to leak, the bulkheads stop the water from flooding the ship. Bulkheads Safety systems A ship may sink if it takes on water. To prevent this, ships have safety features such as bulkheads—walls that divide large areas into smaller ones. Double hull A big ship usually has a double hull, which is like a tire with an inner tube. It gives extra protection if the ship collides with rocks or icebergs. Hull Double hull The steel hull is full of air, which is very light and keeps the ship afloat. That sinking feeling The air inside a ship’s hull makes the ship less dense than the water around it. If the ship hits a rock and rips a hole in its hull, water pours in and replaces the air. This makes the ship more dense and it sinks. Float that boat Going down Submarines are not like other boats— they have to be able to sink or float on command. They do this by filling and emptying their ballast tanks with air or water. Periscope The weight of a submarine’s hull Compressed helps it to sink, air tank Valve but it can’t sink when there is air in the ballast tanks. Most of the air is let out through a valve. Some air is compressed Interior (squashed) into a small holding tank. Water is then pumped into the tanks and the sub sinks. Ballast Water is tank taken in 1 2 Air flows into the ballast tanks. When the sub is underwater, air is pumped back into the ballast tanks until the density of the sub matches that of the water around it. The sub can stay at one level as it moves through the water. Water is forced out. When it’s time to surface, more air is pumped into the tanks, pushing the water out. Once it’s at the surface, air is sucked in to fill the ballast tanks and the sub floats. 3 This ship is taking on water and has started to sink. and the sub sinks. Air fills the tanks and the sub rises. Water is forced out. 47 An oil tanker called Knock Nevis. It’s 1,504 ft (458.4 m) long. Gases and liquids Floating balloons Why do some balloons rise up into the air and others drop to the floor? To understand this you have to look at the gases inside them. alloons b y t ar a He wit h he l i u m Helium This balloon is filled with a gas called helium. Helium is lighter than air, so this balloon floats. d fille re P An airship can rise over 6,500 feet (2,000 meters). That’s lower than an airplane’s usual cruising height of 29,000 feet (8,800 meters). g a s. At parties, helium balloons are tied down so they don’t float off! 48 Heavy air When a balloon is filled with a gas that is lighter than air it floats. When it is filled with a gas that is heavier than air, it sinks. CO2 Carbon dioxide When you breathe out (into a balloon) the air contains more carbon dioxide than normal air, making it heavier. So a balloon you blow up with your breath will sink. Helium facts Helium gas has no smell. It makes up about 7 percent of natural gas. Deep-sea divers breathe in a mixture of helium and oxygen. Helium boils at a very low temperature, -452˚F (-269˚C), and turns to gas. Helium, found in stars, is named after the Greek word for the Sun—helios. Liquid helium is colorless, and very cold. It helps launch space rockets. What is the only element to be discovered in space before it was found on Earth? Floating balloons Flying ships of air An airship is known as a lighter-than-air (LTA) craft. Airships have a main heliumfilled balloon and two other large internal balloons called ballonets. To control how high an airship floats, the ballonets take in or release air. How airships rise and fall Airship rising Ballonets deflate to go higher Air expelled through air valves To rise, the ballonets are closed and deflated. The helium makes the airship float upward. Cold air weighs more because its molecules are closer together. Hot air is lighter because its molecules are farther apart. The balloon holds the hot air. Its shape makes it hard for the hot air to escape. Skirt Propane tanks Helium. How hot-air balloons work Hot-air balloons float upward when the air inside them is heated. This gives the air molecules more energy and they move farther apart, which makes the air lighter. Airship falling Helium Air inflating ballonets Air taken in filling the ballonets To descend back down to Earth, the ballonets are filled with the heavier air, making the airship sink. A flap at the top of the balloon allows hot air to escape and controls how quickly the balloon sinks. Fabric panels are sewn together sideways and lengthwise to give the balloon strength. Burners use propane gas to produce a hot flame, which heats the air inside the balloon. 49 Gases and liquids Roller coaster These rip-roaring rides are powered by gravity itself. They slingshot thrill-seeking passengers along at breathtaking speeds. Going up... Over the top At the top of a hill, roller-coaster cars have high potential energy. This becomes kinetic energy as the roller coaster rolls down the slope. arg hhh As the roller coaster goes up the first, tallest hill (called the lift hill), it’s gradually building up potential energy. There is maximum potential energy at the top of the hill. Some older roller coasters run on intricate wooden scaffolding. Rushing down a steep slope can make you feel almost weightless, which may be quite uncomfortable! Chain reaction Roller-coaster cars don’t have motors. They’re pulled to the top of the first hill by a chain connected to a motor at the top. 50 Where was the world’s first roller coaster? The cars gain speed as they roll down the hill. Roller coaster Wheeeeeeee! Lots of different things affect the way you feel when you’re whizzing around a roller coaster. Flexible metal The tracks and supports of most roller coasters are made from hollow steel. This can be shaped into loops and corkscrews. Shoulder harness Acceleration force Apparent weight Gravity (weight) Safety first All riders are protected by a safety harness. Brakes are built into the track, not the cars— they are used at the end of the ride, or in emergencies. After coming down the first hill, the cars have enough speed to send them around the next loop. This creates “g-force,” which makes the passengers feel much heavier. Cars lose momentum throughout the ride, so the hills have to get smaller. There is maximum kinetic energy at the bottom of the hill. Focus the force The roller coaster track acts as a channel for gravity. When the track slopes down, the car fronts go faster—when it tilts up, the car backs are pulled down, and they go slower. Ultimate experience Thrill seekers in Florida can enjoy the new Rip Ride Rockit roller coaster. It’s very short and powerful, so it can pivot like a skateboard and climb straight uphill. Passengers can choose the music they hear while they’re terrified. Steel track Load wheels Guide wheels Upstop wheels Roller-coaster cars are clamped securely to the rails by three sets of wheels. 51 The very first coaster was an elaborate ice slide built in Russia during the 1600s. Gases and liquids How do planes fly? Hugge,, heavy y machines seem to defy y gravity y by y stay yingg up p in the air! Yet airplanes fly around the world every day. It’s because they y can create the forces they y need to fly. The forces of flight “Aerodynamics” means “the way air moves.” There are four aerodynamic forces—thrust and drag, and lift and weight. Airplanes need to balance them out in order to fly. Thrusting forward Planes need to create thrust to balance out drag. This plane has a propeller to create thrust. As the propeller turns, it draws air past the blades, pulling the plane forward. Engine Thrust Level of plane Cooler air 52 Cockpit Warmer air rises faster, “bumping” the plane upward Propeller A bumpy ride Just like boats bounce over waves, planes can bounce up and down in the air. Called turbulence, this happens when pockets of air move at different speeds. It can be caused by strong winds, storms, or when cold and warm air meet. The biggest jumbo The world’s largest plane is the Airbus A380. At 239½ ft (73 m) long, this jumbo jet can carry up to 853 passengers. It’s 10 times longer than the four-seater Cessna 400. Cessna 400 Airbus A380 What was the first airplane to stay up in the air successfully? How do planes fly? Lifting up Lift is the opposite force to weight. A plane creates most of its lift with its wings. Lift As the plane moves, air flows over its wings. The top of the wing is curved, making the air above the wing move faster than the air under the wing. What does that part do? Every part of a plane has a job to do, from the streamlined nose to the tail fin that keeps the plane steady in the sky. Flaps that come down from the wings are used to increase lift during takeoff and landing. The slow-moving air under the wing pushes up more than the fast-moving air above the wing pushes down. This creates lift. Airflow Ailerons on the back edge of the wings are used to “roll” the plane, to make it turn or keep it level. Tail fin Aileron Fuselage Rudder Weight Wing Flap Elevator A rudder in the plane’s tail turns the plane left or right. Drag Weighing down Weight is caused by gravity pulling down on an object. Everything has weight, even air. The Airbus A380 needs to create a lot of lift to balance out its weight— it’s a whopping 617 tons (560 metric tons). Dragging back Drag is the opposite force from thrust—it slows things down. Imagine trailing your hand in water as you sail along in a boat. You can feel the water push back, or drag, against your hand. Air has the same effect on planes (and anything else that moves). A plane’s smooth surface and streamlined shape help to reduce drag. Elevators in the tail move up and down to balance the position of the nose, keeping the plane level. 53 The Wright Flyer. On its first outing in 1903, it flew for 12 seconds! Gases and liquids Blastoff! Nose cone Space is the final frontier. So far, man has explored only a tiny part of our galaxy, and this has been very difficult, dangerous, and expensive to do. Command module Service module Rocket stage containing lunar module Instrument unit Rocket stage containing fuel What makes rockets go? Engine Most rockets need two different chemicals: a fuel and an oxidizer. When they’re mixed together, they cause a fierce but smooth burn—this is funneled downward, propelling the rocket up. Clamps hold it down while the power builds, so it doesn’t go end over end and crash. At the word “blastoff,” the clamps are removed and the rocket is on its way. Good luck! Rocket stage containing fuel Engines Gravity Thrust Rocket stage 54 When the Apollo lunar-mission crew returned to Earth, they landed in the Pacific Ocean and were rescued by Navy personnel. When was the first liquid-fueled rocket made? Blastoff! Shuttle spacecraft have a winged orbiter, a huge fuel tank underneath, and two rocket boosters that send them into orbit. Space journey After rockets are launched, they use huge amounts of fuel to get into Earth’s orbit. They then release several rocket stages containing fuel so that only the much smaller capsule actually goes into orbit. Or bit 3 The engines have boosted the capsule into orbit. 2 As the fuel is used up, the fuel tanks are released. Rocket blasts off from launch pad. Command module parachutes into the ocean. 1 7 Command module positions itself to reenter Earth’s atmosphere. 5 Command module separates from service module. Space junk Experts believe there are more than 150,000 objects orbiting the Earth—pieces off satellites, bags of garbage, and dropped tools. March 1926, by Dr. Robert H. Goddard in Massachusetts. 6 4 Capsule circles the Earth in orbit. 55 What is energy? What is energy? Energy is what makes everything happen. It is involved in every action that we make. It powers your muscles, runs your car, and lights your home. Without energy you could not ride a bike, watch television, or fly in an airplane. Different types of energy Energy can’t be made, just changed from one type to another. Here are some of the main types. Light is a form of energy that we can see. Most of the energy on Earth comes from the Sun as light. Heat energy is the energy of atoms or molecules vibrating. The hotter an object gets, the faster and more violently the atoms or molecules vibrate. Atoms vibrate as they get hotter. Nuclear energy is stored in atoms. Nuclear energy is used to run power plants that generate electricity. Electromagnetic energy is carried by X-rays, radio waves, and microwaves. 56 Everything is made up of atoms—but what are they? What is energy? Curiosity quiz Look through the “What is energy?” pages and see if you can identify the picture clues below. Gravitational energy is the stored energy in an object that has been lifted but is not allowed to fall. Dams can turn gravitational energy into electrical energy. Kinetic energy is the energy a moving object has. The faster a car moves, the more kinetic energy it has. Electrical energy can travel easily through wires. It is the energy we use to power devices in our homes. Become an expert... on power plants, pages 62–63 on gravity, pages 44–45 57 The smallest particles that something can be broken down into. What is energy? It’s electric! If you flip a switch to make something work, it probably runs on electricity. Most of the energy we use every day is electric. What is electricity? W Electrical energy This magical power source comes from electrons—tiny charged particles on the outside of atoms. They move from atom to atom creating electrical energy, and this energy travels on a circuit. travels very quickly, at 125,000 miles (200,000 km) per second. That’s two-thirds as fast as the fastest thing ever— light! Electric sockets are live. You should never put your finger or an object (other than a plug) into a socket—you might get an electric shock. Electricity passes freely from the socket to the lamp through the wiring. Electrons Starting small To understand electricity, you have to look at the teeny tiny building blocks that everything is made from—atoms. or wha t ? d e ir Plugs have metal prongs that connect with the power supply wired into the wall. r car Atom n ya Elect Electrons ricity flow y s wa s thi 58 ele c tr ical charge. Electricity is passed along wires by electrons. When you supply energy to the wire, it makes the electrons move along it, carrying electric charge with them. Who made the first battery? When you switch on a lamp, electric current flows along the flex to the bulb, lighting it up. It’s electric! Electricity Simple circuit A flashlight works using a simple electrical circuit. Batteries produce electricity, which flows around the circuit to power the bulb so it lights up. When we talk about electricity, we use the same words over and over again. When the switch is on “off,” the circuit is broken and the bulb goes out. Lamp filament Conductor—a material that allows electricity to flow through it easily. Broken circuit Circuit—a path that an electrical current can flow along. Plastic case On Off Batteries To turn off the flashlight the circuit is broken. A Ampere—a basic unit of electrical current. Current—a flow of electricity through a conductor. Power masts Electricity travels from power plants along thick cables often strung between big metal towers. The cables carry very high levels of electricity—enough to kill an adult man if they fell on him. Slide switch When the switch slides to “on,” the circuit is complete and current flows all the way to the bulb, which lights up. V Voltage—a measure of electrical strength. Off Metal switch contacts Metal spring Electricity flows from the batteries and along the metal wire. Birds don’t complete an electrical circuit with the ground like people do, so they can sit on cables without being harmed. 59 An Italian named Alessandro Volta made the first battery in 1800. What is energy? The power of magnets BEWARE: Magnets create an invisible force known as magnetism that repels and attracts certain substances, like iron. Electricity and ! magnetism have a close relationship. ELECTRICAL CHARGE Can you field the force? A magnetic field is the space around a magnet where its force can be felt. The force gets weaker as the field gets farther from the magnet. It is strongest at the two poles. Iron filings reveal the magnetic field around a magnet Poles N S N Opposite poles attract Magnetic Earth S The Earth acts like a gigantic magnet. It has a magnetic north and south pole, although they aren’t in the same place as the geographical poles, but are very close. Over the Earth’s lifetime the magnetic poles have switched around a few times. Magnets have two points where their field is strongest, known as poles. Each magnet has a north and south pole. These can attract and repel other magnets. Similar poles repel and opposites attract. S Similar poles repel Super magnets These are really sticky magnets. They can be natural magnets or electromagnets. The maglev train uses an electromagnet. N E N W S S 60 S A compass uses a magnet as a “needle.” The needle is attracted and points to the magnetic north pole. Which elements are attracted to magnets? Electromagnets A magnet can produce electricity and electricity can create magnetism. An iron bar can become magnetic when an electric wire is wound around it in a coil. A moving magnet can also make an electric current in a coil of wire. Electromagnetic generators are used to create electricity at power plants. The power of magnets Everyday magnets Magnets are used in many everyday items, such as: Audio speakers use electromagnets to make sound vibrations. Some handbags close with magnetic clasps. Credit cards use a magnetic strip to store your information. Central locking in a car uses a series of electromagnets to lock up. The wheel has to keep turning for the dynamo to light the bulb. Wheel power A simple example of an electromagnetic generator is a bicycle dynamo. It uses the kinetic energy produced by the spinning wheel to turn the magnet past a coil of wire. The movement of the magnetic field produces enough electric current to light a bicycle light. Electric current runs up the wire to power the light bulb. Wheel spins The dynamo turns as the wheel spins. The magnet rotates. Iron core Coil of insulated wire surrounds the iron core. Electrical output rd wei or what? Lodestone is a naturally occurring magnet thought to be made when lightning strikes. In 500 BCE Thales of Miletus noticed it because the iron nails in his sandals stuck to it. The insulated wire stops the current from taking a shortcut from loop to loop and keeps it flowing around the core. 61 Iron (Fe), Nickel (Ni), and Cobalt (Co) are all attracted to magnets. What is energy? Power plants There are two kinds of energy— renewable and nonrenewable. Earth will run out of nonrenewable fuels, but renewable energy comes from endless resources such as wind and sun. In Shanghai, China, vast quantities of coal are loaded on a conveyor belt. Burn, burn, burn Most power plants burn nonrenewable fossil fuels like coal, oil, and natural gas. These are formed from fossilized plankton or plants that lived millions of years ago. Fossil fuels release energy from these plants when they’re burned. Smoke and hot gases escape from the chimney. Heat from burning coal turns water in the pipe into steam. Ash collects underneath. The steam drives the turbine. Flow of steam The turbines produce electricity by turning a magnet inside a large coil of wire. Cooling water out Pump The steam passes into a condenser. Crushed coal and hot air Pump brings in cooling water. Ash As the steam condenses to water, it collects in this tank. Flow of water 62 How far does power travel? Cold water in the pipe cools the steam so it condenses. Power plants Dangerous power Nuclear power plants create energy by splitting uranium atoms, which release heat to run the generators that make electricity. Nuclear power is nonrenewable because there is a limited supply of nuclear fuels. The waste from these fuels is radioactive, so they may damage cells and cause cancer. Green power Renewable energy sources will always be there— and they’re less harmful to the environment than fossil fuels. On April 26, 1986, at 1:23 a.m., Reactor Four at Chernobyl Nuclear Power Plant in Ukraine exploded. Over 20 years later, an inspector checks the interior (left). Solar power comes from the Sun. In theory, it could provide all our energy. Hydroelectric power is created by falling water, like a dam or waterfall. Become an expert... Wind power is generated by turbines. Lots of them together make a wind farm. on renewable energy, pages 66-67 Transformer “steps up” the voltage. Tidal power uses water in the form of waves rather than waterfalls. Biofuels (like corn oil) are made from growing things, so they’re renewable. Stretched between towers, cables carry high currents. Power masts are huge steel towers. They have extra wires running along the top to ground lightning. Geothermal power comes from heat deep, deep down toward the Earth’s core. Substations reduce voltage and send power in different directions. On the way... All over the world, rows of masts march across the landscape. They support the high-tension cables that carry electricity from power plants to homes and offices. Electricity is wired to power points in your home. It connects with equipment through a plug. Local grid Cables below ground 63 Power can travel up to 300 miles (480 km) to your home. What is energy? Running out What can you do to save energy? Most of the energy we use comes from burning fossil fuels. But these fuel sources won’t last forever, so we need to start thinking about how we can use less energy, and try to find other ways of providing it. Turbines in a coal-fired power plant without their metal covers. Steam power Electricity that comes from coal is relatively inexpensive to make. In a machine called a pulverizer, the coal is broken down into a fine powder, then burned in a furnace. The furnace heats a boiler to produce steam. The steam powers turbines that run generators to create electricity. Tall pipes are used to drill oil from the ocean floor. Oil and gas We get oil by drilling under the ground— from dry land, or from the ocean floor. Today, we use oil for 38 percent of our energy, either as fuel for heating, or turned into gasoline for cars and planes. Experts think oil reserves will run out in about 40 years. 64 Grow your own fruit and vegetables. Try to eat food that is produced locally. Don’t waste heat. Ask your parents to make sure your home is insulated. Save gasoline. When you can, walk instead of asking for a ride. Turn off your television and computer. Don’t leave them on standby! Switch off lights when you leave a room, and use energy-saving light bulbs. Dry laundry outside instead of using a dryer. Recycle and reuse items such as glass, plastic, and paper. Oil rig Oil reservoir Marine life that has decayed. How much oil can the largest oil rig store? A layer of rock traps the decaying remains, which turn into oil. Running out rd i e w Compressed lignite turns into coal. Compressed peat becomes lignite. Decaying plants form peat. Peat is the earliest stage in the formation of coal. Underground gas Natural gas is also a fossil fuel. It comes from coal beds, marshes, bogs, and oil reserves. The largest reserves of natural gas are shared between Iran and Qatar, although Russia is the world’s biggest gas producer. Natural gas is likely to run out in about 100 years. At the moment, it provides 23 percent of our energy. or what ? In the US, about half of all the electricity used comes from coal-burning power plants. Black diamonds Like diamonds, coal is a form of carbon. Excavated from the ground through deep mines or open pits, it provides 25 percent of the world’s energy supply. If we continue digging coal at the current rate, we have about a 250 years’ supply left in the Earth. Gas facts Easily piped into homes, natural gas is completely clear and odorless. When it burns, it releases lots of energy, which makes it suitable for use in cooking, heating, and cooling. It also gives off fewer harmful substances than other fossil fuels, so it’s slightly greener. 65 The Hibernia platform in the Atlantic Ocean can hold 1.3 million barrels of crude oil. What is energy? Become an expert... Renewable energy Energy made from fossil fuels will eventually run out, but certain types of energy are renewable, which means that we can go on using them forever. on energy-efficient homes, 72–73 Anemometer Low-speed shaft Controller Gear box The wind blows the blades around. df oul le c eop dp dre Electricity is wired to power points in your home. High-speed shaft un Blade eh Wind farms are where lots of turbines are installed in a field or in the sea. Generator On Brake no it o Substations divide power so it can travel in different directions. The transformer sends alternating currents into power lines. Wind power Wind turbines use the power of moving air currents to spin their propellers. These are huge windmill-like blades on top of a tall tower. As they spin, generators inside the turbines make electricity, which is sent via cables underground. The electricity travels underground to a transformer station. When was the first geothermal plant built? de. bla Cables carry high currents between masts. 66 ne Local grid Wind moves faster the higher up you go from the ground. Taller towers generate more electricity. Underground Renewable energy The spillway of a dam is used to control the flow of water. Water from a reservoir flows down a pipe to a turbine. Hydroelectric power A fifth of the world’s electricity comes from hydroelectric power plants. Usually a dam is built to trap a river and create a lake. Water is released at a controlled rate and allowed to flow through a spinning machine called a turbine, which drives an electricity generator. Solar energy Huge glass panels are put on the roofs of buildings to capture energy from the Sun and convert it into electricity. The stronger the sunlight, the more electricity they make. Electricity generator Turbine Geothermal energy The Earth’s crust is a hot place! Some rocks can be as hot as 1,800 ºF (1,000 ºC). Geothermal energy uses the heat from these rocks to generate electricity and heat water. When sunlight lands on a cell, electrons are pushed from one layer to the other creating an electric current. Solar panel Photovoltaic cell Pure silicon doesn’t conduct electricity well. Each cell contains silicon doped (made impure) with phosphorus, which produces free electrons. Silicon doped with boron makes “holes” where electrons are missing in the cell. One of the biggest geothermal areas in the world is Iceland. People can swim next door to this geothermal plant in Iceland since the water is so warm. Biofuels Biofuels come from fast-growing crops, such as corn, sugar cane, and palm oil. These fuels can add to or replace fossil fuels such as diesel or gas. Biofuels have been criticized for taking up land that could be used to grow food. 67 The first plant was built in 1904 in Ladarello, Italy. What is energy? What’s cooking? The stove is probably the most important piece of equipment in the kitchen. Without it, you’d have to eat all your food raw. The oven Heat is a form of energy. It comes from the movement of atoms and molecules. The faster the molecules move around, the higher the temperature. Inside an electric oven are large coils of wire called heating elements. These heat up when electricity travels through them. They are controlled by a thermostat that keeps the temperature inside constant. On a burner, the element is in direct contact with the saucepan, which passes the heat through to the food. Dial controlling the thermostat. Because the broiler element is much closer to the food and gets hotter than the one in the oven, the food cooks quickly. Convection ovens have fans that blow air around and keep the whole oven at the same temperature. Food cooks faster in a convection oven. The oven works by surrounding the food with hot air. Since hot air rises, the top of the oven is slightly hotter than the bottom. When the oven gets too hot, the thermostat turns the heating elements off. It turns them back on again when the oven cools. 68 Can you cook ice cream in an oven without melting it? What’s cooking? Heat’s effect on food Heat changes food, and different foods react to it differently. Cooking is simply delicious experiments in chemistry and physics. Cooking eggs Egg whites and yolks are made of stringy chains of protein floating in water. Chains of protein Each individual chain is twisted and curled up. When you add heat, the chains uncurl and start to link together. Chains of protein unravel and join up. Baking bread A basic bread mixture includes flour, water, and yeast. Yeast is a live, single-celled fungus. Flour, when it mixes with water, releases stretchy gluten. + Sweet treats Many candies are made by simply adding sugar to water and heating the mixture to very high temperatures. + + Yeast is inactive until it comes into contact with warm water. When the bread mix is left in a warm place, the yeast starts feeding on the sugars in flour and releases carbon dioxide gas. As you cook it, the water boils away, leaving a much stronger solution of sugar. Very strong solutions make toffee or hard tack candy. Water boils out of the sugar. Gas is released. The chains form a mesh that traps the water they floated in. The egg is now cooked. The gumlike gluten fills with thousands of gas bubbles and the bread rises. Cooking traps the bubbles in the bread. If you stir the mixture as it cools, it forms crystals. This is how you make fudge, but you leave hard candy to set without stirring. The chains form a mesh. 69 Yes, if you make baked Alaska—ice cream covered in meringue.! What is energy? Keeping cool We keep food cool so it stays fresh, and we keep liquids cool so they’re refreshing to drink. Electricity makes all this possible. 45ºF (7ºC) and above Some foods don’t need to be chilled to stay fresh. Let cheese warm up before you eat it. 32–45ºF (0–7ºC) 32ºF (0ºC) and below 70 Some treats and desserts are served frozen. Eggs are usually stored in the refrigerator door, which is a few degrees warmer than the shelves. Room temperature Dry foods such as beans and pasta keep very well at room temperature. Root vegetables like potatoes don’t need to be refrigerated, but they keep best in a cool place rather than a warm one. Refrigerator The temperature inside a refrigerator is cold enough to slow down the growth of bacteria (germs) in our food, so it stays fresh longer. Dairy products, meat, and fish should always be stored here. Freezer Freezers are cold enough to make your skin freeze! Bacteria can’t multiply in these temperatures, so food stays fresh for months or even years. Most foods are thawed or warmed before you eat them. Lettuce and other salad vegetables go in the door, or in a drawer at the bottom of the refrigerator. Cool coil A long coiled pipe is set into the refrigerator walls. Inside is a gas called tetrafluoroethane, which travels around the fridge soaking up heat. This heat travels to a compressor, and is then released at the Gas coolant back, which is why it feels circulating around fridge warm there. How quickly do bacteria grow at room temperature? Keeping cool Adjustable temperature control Warmed coolant Compressor Control electronics Compressor 71 In just four hours, one bacterium can turn into more than 1,000! What is energy? Energy efficiency Every home needs energy for heating, lighting, cooking, and lots of other things. It’s important not to waste this power—not only because you have to pay for it, but also because the sources of this power may one day run out. Eco living Triple-paned windows have three panes of glass with a layer of air between them. The air stops heat from escaping, so you need less energy to heat the house. The windcatcher channels air into the house, providing ventilation. The aluminum tubing reflects light inside. Sustainable homes are designed to be better for the environment. They have lots of features that save energy and water. They produce fewer carbon emissions and are also cheaper to run. The outside of the roof is covered in photo-voltaic and solar panels. These generate electricity for the whole house. 72 The “Lighthouse” is built with materials that absorb heat during the day and give it out at night. A biomass boiler burns wood pellets for heating and hot water during the winter. What are carbon emissions? Energy efficiency Batteries In your home We can all do things to make our homes more energy efficient. A lot of energy is used to heat a house. Ask your parents to lag your attic with insulation to keep heat in. You can also insulate walls and floors, plug gaps around doors and windows, and install double-paned windows. Thermograms are pictures that show hot things as white and yellow and cold things as blue. The hottest part of this house is its windows, because heat is escaping through them. When rain hits the roof, it collects in a gutter and runs down a pipe into a recycling tank. The water is used in a washing machine. Every household uses batteries to power all kinds of things—but batteries eventually run out. So how should you dispose of them? Change old batteries right away. Batteries contain chemicals that may leak and ruin the gadget. Insulating a loft Become an expert... Don’t trash batteries. Recycle them instead—it’s better for the environment. Batteries should never be thrown onto a fire— they might explode. on saving energy, pages 64–65 on renewable energy, pages 66–67 When things break… However energy-efficient you are, electrical goods will eventually wear out. But some items are simply too dangerous to throw away. Old refrigerators contain gases that are harmful if they leak. The safest way to get rid of a broken refrigerator is to contact your local recycling center. Broken fridges must be taken apart carefully so they don’t release harmful gases. Make a difference If you get a new computer or cell phone but there’s nothing wrong with the one you had, you can donate the old one to charity. Go online to find charities, schools, and groups that can make good use of your unwanted equipment. 73 Gases containing carbon that are released into the air and may cause global warming. Light and sound Light and sound of What is light? Light is a type of energy called electromagnetic radiation, or EMR. “Electromagnetic” means it’s made up of electrical and magnetic energy, and “radiation” means it spreads out from a source. Atoms—the tiny particles that make up everything around us— are that source. Atoms that have too much energy can get rid of it in the form of light. ’s n u give out l s m o ts ato See the light Light is made up of different colors, but light cannot be seen unless it hits our eyes. Light travels in straight lines, but it can change direction. When light passes through a prism (usually a threedimensional glass triangle), it bounces off the sides of the prism and bends. Some colors in light bend more than others, so they spread out and you can see the different colors. Th e S A glass prism splits the light into colors. Most of what we know about the world we learn by seeing and hearing. Everything we see needs light, and everything we hear involves sound. They can both reach us by traveling in waves. t. h lig The speed of light Light travels in waves, a bit like waves that travel through water. Light travels faster than anything else in the universe— an amazing 186,000 miles per second (300,000 km per second)! It takes just eight minutes for light from the Sun to reach Earth. 74 What is refraction? Light doesn’t always behave like a wave. Sometimes it behaves like it’s made up of particles, so it spreads out more like a spray of water from a hose than waves in the sea. Secrets of sound Light and sound Curiosity quiz When something vibrates, it squeezes and stretches the air around it, sending out waves that we hear as sound. Look through the “Light and sound” pages and see if you can identify the picture clues below. Echolocation Some animals use sound to find their way around. This is called echolocation. Bats send out high-pitched squeaks that bounce off their surroundings. If their echo comes back quickly, it means there’s something nearby. Cymbals make large waves, which means a loud sound! The speed of sound Sound travels more slowly than light, at 1,125 ft per second (343 meters per second) in air. But the speed changes, depending on what the waves are traveling through. They can move four times faster in water than in air. Become an expert... on visible light, pages 76–77 on how ears hear, pages 90–91 75 Refraction is when light waves bend, such as in a prism. Light and sound Now you see it… Light waves (or electromagnetic waves) are all different lengths, but each length travels at the same speed. Some light waves are too short or too long for us to see. The light we can see is called “visible spectrum” light. Blue Cyan Green Red ... And now you don’t Our eyes can see only light waves of a certain size—if they’re longer or shorter, they’re invisible. We use invisible electromagnetic waves in our lives every day. Radio waves Radio waves carry sound and images through the air. Radios, televisions, and cell phones all use radio waves. The longest radio waves can be 100,000 times longer than the shortest ones. 76 Light of many colors Visible light is made up of waves of different lengths. Each length appears as a separate color. For example, red waves are long and blue rays are short. Light contains an endless amount of colors. The only limit is on how well your eye and brain can tell one wavelength from another. Microwaves Microwaves heat water molecules in food and liquid, but they pass straight through glass and plastic. So when you heat soup in a microwave oven, it’s not the microwaves that make the bowl hot, it’s the hot soup inside. What is white light? Infrared waves Infrared waves carry heat. We can see infrared waves with night-vision goggles or special cameras, both of which are designed to pick up heat rather than light. When you get near something hot, it’s infrared rays you feel on your skin. Prisms and rainbows Light bends when it passes through a prism. Each color bends at a different angle, so they separate out and form a rainbow. I can see a rainbow When it’s raining or misty, the tiny droplets of water in the air act like hundreds of prisms, breaking down sunlight into its different wavelengths. Each drop of water, depending on where it is, bounces a particular color into your eyes. You see these colors as the bands in a rainbow. Visible Everything we see can be seen because visible light waves bounce off objects. Light waves can come from the Sun and from light bulbs. Ultraviolet (UV) rays Ultraviolet waves come straight from the Sun. Some UV waves can burn your skin and, over time, cause wrinkles and cancer. That’s why it’s wise to cover up when you go outside in summer and put sunscreen on your skin to block out harmful rays. A well-cut diamond is the best prism there is. Because it has so many different surfaces, light bounces around inside, creating bright, sparkly colors. X-rays X-ray waves pass through most things, but not bones, teeth, or metal. When doctors want to look at your bones, they take X-ray pictures to see if anything is out of place or broken. Gamma rays Gamma rays can bore through solid objects and kill living cells. Doctors use them in radiation treatments to destroy cancer cells. Gamma rays are also released when nuclear bombs explode. All the colors of visible light appearing together. Visible spectrum Now you see it... 77 Light and sound Light and bubbles When light hits the surface of a bubble, it reflects off both the outside AND the inside of its skin, producing the effect of swirling, shimmering colors. Bubble colors There are different colors in a bubble (purple, yellow, and blue) from those in a rainbow (green, blue, and red). This is because a rainbow splits white light into separate colors, but a bubble subtracts colors from light. If red is subtracted, you see the greeny-blue that is left behind. Hands On Make your own bubble solution by mixing half a cup of dishwashing liquid with four cups of water and four tablespoons of glycerine. 78 These bubbles are on the surface of a soap and water solution. Color secrets You can tell how thick a bubble is by the colors it reflects. The blue pa