GenreGenre Comprehension SkillComprehension Skill Text FeaturesText Features Science ContentScience Content Nonfi ctionNonfi ction Cause and EffectCause and Effect • Captions• Captions MatterMatter • Diagram• Diagram • Text Boxes• Text Boxes • Glossary• Glossary Scott Foresman Science 3.10Scott Foresman Science 3.10 ì<(sk$m)=bdidhb<ì<(sk$m)=bdidhb<ISBNISBN 0-328-13837-10-328-13837-1 +^-Ä-U-Ä-U+^-Ä-U-Ä-U
Vocabulary Extended Vocabulary What did you learn? atom balsa wood buoyancy cargo ship 1. Why do some objects fl oat in water? density displace element hull 2. Where is water pressure strongest? mass steel matter swim bladder 3. Why do ships have large, hollow hulls? periodic table withstand by Nairobi Toller pressure 4. In this book you property have read about how density and volume buoyancy are related. Write to explain how an object’s density affects its buoyancy in water. Include details from the book. 5. Cause and Effect Submarines adjust their density to control their buoyancy. What is the effect of a Picture Credits Every effort has been made to secure permission and provide appropriate credit for photographic material. submarine filling its tanks with water? The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd). Opener: Lester Lefkowitz/Corbis ; 1 Doug Wilson/Corbis; 5 Doug Wilson/Corbis; 9 (BR) ©SPL/Photo Researchers, Inc.; 10 Lester Lefkowitz/Corbis. Scott Foresman/Dorling Kindersley would also like to thank: 15 (CA) IFREMER, Paris/DK Images. Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson. ISBN: 0-328-13837-1 Copyright © Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025. 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05
What You Already Know Everything you see, smell, or touch is matter. Volume is the amount of space an object takes Many things you cannot see, smell, or touch are up. Volume is most often measured in liters. matter too. Matter is anything that takes up space Density is a property that measures the and has mass. You can observe the properties amount of matter in a certain amount of space. of matter. Two objects of the same volume can have Matter comes in three forms: solid, liquid, different densities because of their mass. and gas. Solid matter particles are packed tightly Buoyancy is a property of matter that together. Liquid matter particles are loosely measures how well an object floats. Objects connected. Gaseous matter particles are not more dense than water sink. Objects less dense connected. When gas is put into a closed space, than water float. it expands, pushing against the sides of the container. This pushing is called pressure. In this book you will learn more about Some kinds of matter are made up of only density, buoyancy, and other properties of matter one type of particle. This single type of matter is in water. These are all things that engineers must called an element. Elements are made up of even think about in order to smaller particles called atoms. There are more build ships that float. than one hundred different elements. Scientists organize the elements in a periodic table, or chart of elements. Properties of matter can be measured. Mass is the amount of matter an object has. It can be measured with a balance. 2 3
Floating and Sinking Have you ever wondered how huge ships are able to float? Even cargo ships loaded down with heavy goods float. Buoyancy and density make floating possible. Engineers who build ships must think about how to make heavy things, such as cargo ships, have a low enough density to float in water. Most ships are made with lots of metal screws. But if you throw a metal screw into water, it will sink. At first you may think this is because the screw is heavy. But weight alone does not make it sink. The screw sinks because of its density. The density of most metal is greater than the density of water. Most ships are made of metal too. It does not seem as though ships should float. All that metal and all those screws sink on their own. How do the engineers combine them so a ship can float? Screws sink because they have a greater density This huge cargo ship fl oats than water. because it has a lot of buoyancy. 4 5
Matter and Density Which matter has the The secret to making objects float is density. lowest density? Which has the greatest? Density is the amount of mass an object has in a certain volume. One liter of water has a mass A cork fl oats on oil. of 1 kilogram (kg). The same volume of steel has a mass of nearly 8 kg. The mass of a one-liter volume of balsa wood is just 1 kg. A plastic block 5 sinks in oil but A solid object will float on the surface floats on water. of a liquid if it has a lower density A grape sinks in than the liquid. Balsa wood is less oil and water but floats on syrup. dense than water. So balsa wood floats on water. Steel is denser Not all liquids have the same density. Some than water. It sinks in water. liquids have more mass and a higher density than others. Syrup is more dense than water. Water is more dense than oil. Liquids of different densities will separate into layers when poured cooking oil into the same container. The lower-density liquids float on top. The higher-density liquids water sink to the bottom. Place solid objects in the same container. Then syrup you can see how dense they are in comparison Liquids of different with the other objects and liquids. The more densities separate into dense objects will sink lower in the container in layers when poured into the same glass. the same way more dense liquids sink lower. 6 7
Forces in Water The upward force of the water makes a cargo ship buoyant. What happens when you place an object into water? It pushes aside, or displaces, some of the weight water. The volume of water displaced equals the volume of the object. As a stone sinks in water, it upward force pushes aside an amount of water equal to its own volume. Even floating objects displace an amount of water equal to their volume. Upward force creates buoyancy. Buoyancy Objects feel lighter as you lower them into partly supports the object. The amount of water. This is because the water pushes against upward force depends on the amount of water them with an upward force. Objects sink until this pushed aside by the object. The more water force balances their weight. But some objects sink something displaces, the greater the upward to the bottom. This is because they are denser force on it. If the upward force is equal to the than water. The upward force of the water is not weight of the object, the object floats. strong enough to balance the object’s weight. This peach has displaced Archimedes only the amount of water The Greek scientist equal to its weight. The Archimedes discovered peach is buoyant because that objects get an the upward force of the upward force from water balances its weight. displaced water. He noticed this when he took a bath. 8 9
Shape and Volume Sink or Float You already know that steel is more dense A piece of clay shaped into a ball will sink. But the same piece of clay shaped like a ship’s than water. But steel can be shaped in a way that hull will fl oat. It has enough volume inside increases its volume. The volume of an object to displace enough water to carry a can increase, yet its mass can stay the same. That cargo of marbles too. decreases the object’s density. A clay ball and The body, or hull, of a ship is designed with marbles sink. a huge open space in the front and bottom. The ship’s hull takes up a lot of space but weighs very little for its size. It contains a large volume of air, Boat-shaped clay fl oats and which lowers the density of the ship. The density holds marbles. is now less than water, so the ship can float! The huge, hollow hull on this cargo ship allows it to fl oat. The large volume of the hull means the ship displaces a lot of water. All the displaced water creates a powerful upward force that supports the ship. If the same amount of steel used to build a ship were shaped differently, would it float? A solid block of steel is much more dense than water. If it were put into water, it would sink. 10 11
Controlling Buoyancy People have air and organs in their bodies that make them less dense than water. This The density of submarines, human divers, allows them to float. Divers must wear belts and fish can be adjusted to control buoyancy. with weights on them to increase their density. A ship’s hull is full of air. This helps it float. Then they are able to sink below the surface. Submarines can float or sink. They use special Most fish are able to adjust their own tanks to do this. These tanks can be filled with buoyancy. They can do this using an organ called water or air. When the tanks are full of water, a swim bladder. When a fish swims deep, water the submarine becomes more dense than water. pressure pushes gas out of the bladder. The fish It sinks. When water becomes more dense and sinks. To rise to the is released from the surface, gas fills the bladder. This makes the fish tanks, the submarine less dense so it can float. becomes less dense, Then it floats. Divers use weighted belts so they can control their buoyancy. Submarine tanks fi ll with water to become more dense and sink. 12 13
Water Pressure Water presses down on objects. This pressing force, or pressure, becomes stronger in deeper water. You can experiment with water pressure using a plastic tube and water. Put three holes in the tube. Put one at the bottom, one in the middle, Submersibles are strong and one at the top. Fill the tube with water. Watch enough to withstand to see how far the water shoots out of each hole. water pressure at the bottom of the ocean. The water from the bottom hole shoots out the farthest. That is where the water pressure is You can feel water pressure in your ears greatest. The water pressure is weaker near the when you swim. People cannot swim very deep top, so the water does not shoot out as far. underwater. The pressure is too strong. We use submarines to travel in deep water. They are There is a weak flow from strong enough to handle the water pressure. the top hole in this plastic Yet not even a submarine is strong enough bottle and a stronger flow from the lower holes. to withstand the pressure at the bottom of the ocean. Only small, very strong machines called submersibles can withstand the pressure. Maybe someday people will be able to travel to the bottom of the ocean safely. For now, we must learn more about ways that make boats float. Density, volume, buoyancy, and water pressure help engineers build ships that can float. 14 15
Vocabulary Extended Vocabulary What did you learn? Glossary atom balsa wood buoyancy cargo ship 1. Why do some objects fl oat in water? balsa wood strong and light type of wood density displace element hull 2. Where is water pressure strongest? cargo ship a ship that carries goods from mass place to placesteel matter swim bladder 3. Why do ships have large, hollow hulls? displaceperiodic tableto move from its usual placewithstand pressure 4. In this book you property have read about how density and hull body or frame of a ship buoyancy are related. Write to explain volume how an object’s density affects its steel strong and hard metal made of buoyancy in water. Include details iron mixed with carbon from the book. swim bladder an organ in a fish that helps it 5. Cause and Effect Submarines control its own density by taking adjust their density to control their in or releasing gas buoyancy. What is the effect of a Picture Credits Every effort has been made to secure permission and provide appropriate credit for photographic material. submarine filling its tanks with water? The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.withstand to stand up to something Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd). Opener: Lester Lefkowitz/Corbis ; 1 Doug Wilson/Corbis; 5 Doug Wilson/Corbis; 9 (BR) ©SPL/Photo Researchers, Inc.; 10 Lester Lefkowitz/Corbis. Scott Foresman/Dorling Kindersley would also like to thank: 15 (CA) IFREMER, Paris/DK Images. Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson. ISBN: 0-328-13837-1 Copyright © Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025. 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05 16
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