Scott Foresman Science 3.10

Genre Comprehension Skill Text Features Science Content

Nonfi ction Cause and Effect Captions

Diagram

Text Boxes

Glossary

Matter

ISBN 0-328-13837-1

1. Why do some objects fl oat in water?

2. Where is water pressure strongest?

3. Why do ships have large, hollow hulls?

4. In this book you have read about how density and buoyancy are related. Write to explain how an objects 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 submarine fi lling its tanks with water?

What did you learn?Extended Vocabularybalsa woodcargo shipdisplacehullsteelswim bladderwithstand

Vocabulary

atombuoyancydensityelementmassmatterperiodic tablepressurepropertyvolume

Picture CreditsEvery effort has been made to secure permission and provide appropriate credit for photographic material. 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 anyprohibited 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 toPermissions 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

13837_01-04_CVR_FSD.indd Cover213837_01-04_CVR_FSD.indd Cover2 05/21/2005 13:49:0605/21/2005 13:49:06

by Nairobi Toller

13837_05-20_FSD.indd 113837_05-20_FSD.indd 1 05/21/2005 13:51:0405/21/2005 13:51:04

2

What You Already Know

Everything you see, smell, or touch is matter. Many things you cannot see, smell, or touch are matter too. Matter is anything that takes up space and has mass. You can observe the properties of matter.

Matter comes in three forms: solid, liquid, and gas. Solid matter particles are packed tightly together. Liquid matter particles are loosely connected. Gaseous matter particles are not connected. When gas is put into a closed space, it expands, pushing against the sides of the container. This pushing is called pressure.

Some kinds of matter are made up of only one type of particle. This single type of matter is called an element. Elements are made up of even smaller particles called atoms. There are more 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.

13837_05-20_FSD.indd 213837_05-20_FSD.indd 2 05/21/2005 13:51:1205/21/2005 13:51:12

3

Volume is the amount of space an object takes up. Volume is most often measured in liters.

Density is a property that measures the amount of matter in a certain amount of space. Two objects of the same volume can have different densities because of their mass.

Buoyancy is a property of matter that measures how well an object fl oats. Objects more dense than water sink. Objects less dense than water fl oat.

In this book you will learn more about density, buoyancy, and other properties of matter in water. These are all things that engineers must think about in order to build ships that fl oat.

13837_05-20_FSD.indd 313837_05-20_FSD.indd 3 05/21/2005 13:51:1305/21/2005 13:51:13

4

Floating and SinkingHave you ever wondered how huge ships are

able to fl oat? Even cargo ships loaded down with heavy goods fl oat. Buoyancy and density make fl oating possible. Engineers who build ships must think about how to make heavy things, such as cargo ships, have a low enough density to fl oat in water.

Most ships are made with lots of metal screws. But if you throw a metal screw into water, it will sink. At fi rst 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 fl oat. All that metal and all those screws sink on their own. How do the engineers combine them so a ship can fl oat?

Screws sink because they have a greater density than water.

13837_05-20_FSD.indd 413837_05-20_FSD.indd 4 05/21/2005 13:51:1505/21/2005 13:51:15

5

This huge cargo ship fl oats because it has a lot of buoyancy.

13837_05-20_FSD.indd 513837_05-20_FSD.indd 5 05/21/2005 13:51:2605/21/2005 13:51:26

6

Matter and DensityThe secret to making objects fl oat is density.

Density is the amount of mass an object has in a certain volume. One liter of water has a mass 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 15 kg.

A solid object will fl oat on the surface of a liquid if it has a lower density than the liquid. Balsa wood is less dense than water. So balsa wood fl oats on water. Steel is denser than water. It sinks in water.

cooking oil

Liquids of different densities separate into layers when poured into the same glass.

syrup

water

13837_05-20_FSD.indd 613837_05-20_FSD.indd 6 05/21/2005 13:51:3205/21/2005 13:51:32

7

A cork fl oats on oil.

A grape sinks in oil and water but fl oats on syrup.

A plastic block sinks in oil but fl oats on water.

Which matter has the lowest density? Which has the greatest?

Not all liquids have the same density. Some 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 into the same container. The lower-density liquids fl oat on top. The higher-density liquids sink to the bottom.

Place solid objects in the same container. Then you can see how dense they are in comparison with the other objects and liquids. The more dense objects will sink lower in the container in the same way more dense liquids sink lower.

13837_05-20_FSD.indd 713837_05-20_FSD.indd 7 05/21/2005 13:51:3605/21/2005 13:51:36

8

Forces in WaterWhat happens when you place an object into

water? It pushes aside, or displaces, some of the water. The volume of water displaced equals the volume of the object. As a stone sinks in water, it pushes aside an amount of water equal to its own volume. Even fl oating objects displace an amount of water equal to their volume.

Objects feel lighter as you lower them into water. This is because the water pushes against them with an upward force. Objects sink until this force balances their weight. But some objects sink to the bottom. This is because they are denser than water. The upward force of the water is not strong enough to balance the objects weight.

This peach has displaced only the amount of water equal to its weight. The peach is buoyant because the upward force of the water balances its weight.

13837_05-20_FSD.indd 813837_05-20_FSD.indd 8 05/21/2005 13:51:3905/21/2005 13:51:39

9

ArchimedesThe Greek scientist Archimedes discovered that objects get an upward force from displaced water. He noticed this when he took a bath.

Upward force creates buoyancy. Buoyancy partly supports the object. The amount of upward force depends on the amount of water pushed aside by the object. The more water something displaces, the greater the upward force on it. If the upward force is equal to the weight of the object, the object fl oats.

The upward force of the water makes a cargo ship buoyant.

weight

upward force

13837_05-20_FSD.indd 913837_05-20_FSD.indd 9 05/21/2005 13:51:4205/21/2005 13:51:42

10

Shape and VolumeYou already know that steel is more dense

than water. But steel can be shaped in a way that increases its volume. The volume of an object can increase, yet its mass can stay the same. That decreases the objects density.

The body, or hull, of a ship is designed with a huge open space in the front and bottom. The ships hull takes up a lot of space but weighs very little for its size. It contains a large volume of air, which lowers the density of the ship. The density is now less than water, so the ship can fl oat!

The huge, hollow hull on this cargo ship allows it to fl oat.

13837_05-20_FSD.indd 1013837_05-20_FSD.indd 10 05/21/2005 13:51:4405/21/2005 13:51:44

11

Sink or FloatA piece of clay shaped into a ball will sink. But the same piece of clay shaped like a ships hull will fl oat. It has enough volume inside to displace enough water to carry a cargo of marbles too.

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 fl oat? A solid block of steel is much more dense than water. If it were put into water, it would sink.

A clay ball and marbles sink.

Boat-shaped clay fl oats and holds marbles.

13837_05-20_FSD.indd 1113837_05-20_FSD.indd 11 05/21/2005 13:51:5005/21/2005 13:51:50

12

Controlling BuoyancyThe density of submarines, human divers,

and fi sh can be adjusted to control buoyancy. A ships hull is full of air. This helps it fl oat.

Submarines can fl oat or sink. They use special tanks to do this. These tanks can be fi lled with water or air. When the tanks are full of water, the submarine becomes more dense than water. It sinks. When water is released from the tanks, the submarine becomes less dense, Then it fl oats.

Submarine tanks fi ll with water to become more dense and sink.

13837_05-20_FSD.indd 1213837_05-20_FSD.indd 12 05/21/2005 13:51:5205/21/2005 13:51:52

13

Divers use weighted belts so they can control their buoyancy.

People have air and organs in their bodies that make them less dense than water. This allows them to fl oat. Divers must wear belts with weights on them to increase their density. Then they are able to sink below the surface.

Most fi sh are able to adjust their own buoyancy. They can do this using an organ called a swim bladder. When a fi sh swims deep, water pressure pushes gas out of the bladder. The fi sh becomes more dense and sinks. To rise to the surface, gas fi lls the bladder. This makes the fi sh less dense so it can fl oat.

13837_05-20_FSD.indd 1313837_05-20_FSD.indd 13 05/21/2005 13:51:5505/21/2005 13:51:55

14

Water PressureWater 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, and one at the top. Fill the tube with water. Watch to see how far the water shoots out of each hole. The water from the bottom hole shoots out the farthest. That is where the water pressure is greatest. The water pressure is weaker near the top, so the water does not shoot out as far.

There is a weak fl ow from the top hole in this plastic bottle and a stronger fl ow from the lower holes.

13837_05-20_FSD.indd 1413837_05-20_FSD.indd 14 05/21/2005 13:52:0305/21/2005 13:52:03

15

Submersibles are strong enough to withstand water pressure at the bottom of the ocean.

You can feel water pressure in your ears when you swim. People cannot swim very deep underwater. The pressure is too strong. We use submarines to travel in deep water. They are strong enough to handle the water pressure.

Yet not even a submarine is strong enough 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 fl oat. Density, volume, buoyancy, and water pressure help engineers build ships that can fl oat.

13837_05-20_FSD.indd 1513837_05-20_FSD.indd 15 05/21/2005 13:52:0605/21/2005 13:52:06

16

Glossarybalsa wood strong and light type of wood

cargo ship a ship that carries goods from place to place

displace to move from its usual place

hull body or frame of a ship

steel strong and hard metal made of iron mixed with carbon

swim bladder an organ in a fi sh that helps it control its own density by taking in or releasing gas

withstand to stand up to something

13837_05-20_FSD.indd 1613837_05-20_FSD.indd 16 05/21/2005 13:52:0905/21/2005 13:52:09

1. Why do some objects fl oat in water?

2. Where is water pressure strongest?

3. Why do ships have large, hollow hulls?

4. In this book you have read about how density and buoyancy are related. Write to explain how an objects 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 submarine fi lling its tanks with water?

What did you learn?Extended Vocabularybalsa woodcargo shipdisplacehullsteelswim bladderwithstand

Vocabulary

atombuoyancydensityelementmassmatterperiodic tablepressurepropertyvolume

Picture CreditsEvery effort has been made to secure permission and provide appropriate credit for photographic material. 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 anyprohibited 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 toPermissions 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

13837_01-04_CVR_FSD.indd Cover213837_01-04_CVR_FSD.indd Cover2 05/21/2005 13:49:0605/21/2005 13:49:06

previous: next: