Physical SciencePhysical Science by Ann J. Jacobsby Ann J. Jacobs GenreGenre Comprehension SkillComprehension Skill Text FeaturesText Features Science ContentScience Content Nonfi ctionNonfi ction SummarizeSummarize • Captions• Captions Forces in MotionForces in Motion • Chart• Chart • Glossary• Glossary Scott Foresman Science 3.12Scott Foresman Science 3.12 ì<(sk$m)=bdiebi<ì<(sk$m)=bdiebi<ISBNISBN 0-328-13841-X0-328-13841-X +^-Ä-U-Ä-U+^-Ä-U-Ä-U
Vocabulary What did you learn?Forces and Motion force 1. What is the difference between constant speed and variable speed?by Ann J. Jacobs friction gravity 2. Would it take more force to begin moving an empty wagon or a wagon loaded with magnetism pumpkins? Why? motion 3. What is the difference between a contact force position and a non-contact force? Give examples of each. relative position 4. In this book you have read about work and simple machines. Write to speed explain how simple machines make work easier work without lessening the amount of work that gets done. Use examples from the book. 5. Summarize Turn to p. 11. Summarize the Photographs: Every effort has been made to secure permission and provide appropriate credit for forces used when riding a bike. photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Unless otherwise acknowledged, all photographs are the property of Scott Foresman, a division of Pearson Education. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R) Background (Bkgd) Opener: ©Allsport Photography/Getty Images; 2 ©David Young-Wolff/PhotoEdit; 4 ©Roy Ooms/ Masterfile Corporation; 5 ©John Elk/Bruce Coleman Inc.; 6 (TL) ©Richard Megna/Fundamental Photographs, (CR) ©Stone/Getty Images, (BL) ©Tom Szuba/Masterfile Corporation; 7 ©Kunst & Scheidulin/Age Fotostock; 8 ©Jim Cummins/Corbis; 10 ©Rolf Bruderer/Corbis; 11 ©Stone/Getty Images; 12 ©Hennie Wiggers/Zefa/Masterfile Corporation; 14 ©Taxi/Getty Images; 15 AlaskaStock; 16 ©Bob Daemmrich/Corbis; 17 ©DK Images; 18 (CL) Getty Images, (R) ©Tony Freeman/PhotoEdit; 20 Corbis; 22 ©Keith Pritchard/Alamy Images; 23 ©Neil Rabinowitz/Corbis ISBN: 0-328-13841-X 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 permissions, 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 happens when things change position? When Things Move Suppose you spin a top. You can tell it moves because its location changes. It starts in your hand. Then it spins across the ground. If an object is in a new location, its position has changed. The top is in motion as its position changes. A top also has circular motion. This means it moves in circles around a central point. Ways of Looking at an Object’s Position The position, direction, and movement of an object depend on how you look at it. For example, as you walk down a hall, a water fountain may be in front of you. After you walk by it, it is behind you. As you keep walking, the fountain seems to be moving away. A map can help you locate things. A map shows the position of objects in relation to each other. Look at the path on the map above. Tell how you would get from the classroom to the lunch room. Use position words like forward, left, right, and behind to explain your trip. 2 3
Positions of Moving Objects Look at the train below. The locomotive is in front. When one thing depends on another thing Two cars are being pulled behind it. Could the cars for its meaning, we say it is relative. Relative move in front of the locomotive? They could if the position is the position of one object compared train started moving backward. Relative position can with the position of other objects. Look at car 64 change if objects start moving in a new direction. below. Its relative position is in front of the other cars. Another car might be leading the race. Then you would say car 64 is behind the lead car. The relative position of car 64 changes depending on the position of other cars. 4 5
How Fast Things Move Constant Speed Speed is how fast an object changes its position. Objects can move at a constant speed. This means Speed can be fast. A jet plane moves fast. Speed can that they do not change how fast or slow they move. be slow. Honey moves slowly. Some things have such a They are always changing position. The rate at slow speed that you can’t see them move! which they change position stays the same. Variable Speed The arms of a tuning fork move very fast. Bumper cars move at a variable speed. An object moving at a variable speed changes speed as it moves. Bumper cars can speed up, slow down, or stop. Honey moves at a slow speed. The motion of these flowers is too slow to see. 6 7
How does force The mass of an object affects how it moves. You don’t need much force to begin pushing an empty affect motion? cart. When the cart is full of food, it has more mass. Now more force is needed to begin moving the cart. The Causes of Motion As the cart moves, its wheels rub against the floor. A force is any push or This causes friction. Friction is a contact force that pull. A force can change slows an object’s motion. Smooth surfaces produce less an object’s position. It can friction than rough ones. Friction is helpful when you change the direction of an want to slow something down. object’s motion too. Most forces you use are contact forces. To push or pull an object, you must More force is needed touch it. A bat makes contact to push three carts with a ball to move it. than to push just one. The more force you use, the more an object’s motion changes. The harder you push on a cart, the faster it goes! 8 9
Motion and Combined Forces Lots of forces cause a bike to change its motion. You know that pushes, pulls, and friction can You push on the pedals. You push on the handlebars change an object’s motion. Now think about the and shift your weight to turn. Friction between the forces in tug-of-war. Your team’s pull is a force in tires and the ground slows your forward motion. one direction. The other team’s pull is a force in the Going up hills takes more force. You may gain too other direction. If the forces are the same, the rope much speed going down hills. You pull on the brakes doesn’t move. to slow down. All these forces work together to keep Suppose everyone on your team pulls together to your bike moving. move the rope. The rope will move in your direction if you have the stronger force. So get more friends to help! 10 11
Gravity and Magnetism The pull of gravity also depends on matter. Objects A non-contact force is a push or pull that affects an with more matter have more mass. The more mass, object without touching it. Gravity is a non-contact the stronger the pull of gravity. force that pulls objects toward each other. Gravity Magnetism is another non-contact force. Magnets pulls everything on Earth toward Earth’s center. pull on objects with certain kinds of metal such as iron Weight is the amount that gravity pulls on an in them. You might use a magnet to pull a steel paper object. Objects weigh less on the Moon because the clip across your desk. Steel is a metal with iron in it. Moon has less gravity than Earth. The pull of gravity Magnets do not affect objects that lack these metals. is less the farther you are from the center of Earth. You weigh less on top of a mountain than you do at it’s base. This magnet does not attract crayons since they lack metal the magnet can attract. This magnet attracts paper clips because they have iron. Gravity pulls skydivers toward the ground. 12 13
How do simple machines affect work? Work In science, work means using force that moves an object. You do work when you rake leaves or kick a ball. How much work you do depends on how much force you use. It also depends on how far you move an object. Work is NOT done if an object does not move. Try pushing a big snowball. If the snowball does not move, no work is done. You may be using force, but you are not doing work. When Work Is Done How much work do you do in a day? To find out, Activity Work you would have to keep track of all the pushing and Thinking about a math problem No pulling you do. Then you would have to see how far Turning a jump rope Yes those pushes and pulls moved things. Holding a puppy No Putting a book on a shelf is work. What if you put Lifting a puppy Yes the book on a shelf twice as high? You would do twice Pulling on a locked door No as much work! You would also do twice as much work Opening an if you put a book that weighed twice as much on the unlocked door Yes Trying to scoop lower shelf. rock-hard ice cream No 14 15
Some Simple Machines Wedge Machines can’t reduce the amount of work that A wedge is a simple machine. It is used to split, needs to be done. But they can help make your work cut, or fasten things. A wedge has one or two easier. Here are six kinds of simple machines. slanted sides that form a sharp edge. A Inclined Plane wedge can move through material and separate it. A knife is a wedge that Look at the man pushing the cart below. Without can cut a pie. An axe head is a the ramp, the man would have to lift the cart into the wedge that can split wood. truck. That would take a lot of effort. He is using a machine called an inclined plane. An inclined plane, or ramp, is a slanting surface. It connects a low spot to a higher one. The mover pushes with less force, but he must push for a longer distance. The same amount of work gets done, but with less effort. 16 17
Screw A screw is an inclined plane wrapped around a Support center post. The spiral slide in the picture looks like a big screw. Screws are used to hold things together. They are used to raise and lower things too. The lid on a jar is a screw. The lid raises as you open the jar. The lid lowers as you close the jar. Lever A lever is another simple machine. A lever is a bar that rests on a support. Levers lift and move things. A seesaw is a lever. Push down on one side of a seesaw. Then watch the person on the other side go up! 18 19
More Simple Machines The rides you see below both use a big wheel and axle. Instead of turning the wheel, a motor in Wheel and Axle these rides turns the axle. The motor turns the axle Whenever you open a door, you use a simple a small distance. But the distance the axle turns the machine. It is called a wheel and axle. The doorknob wheel is great. This makes the ride fun. The motor is a wheel. The post that attaches to its center is an must put a great force on the axle to do this. axle. Turning the knob takes less force than turning the small axle with your fingers. Since the knob is larger, however, you must turn it a longer distance. Do you think the people on this ride are having fun? 20 21
Pulley You live in a world of motion. Look around. What is moving quickly? What is moving slowly? What Pulleys are simple machines that can help move simple machines will you use today to make moving things in the right direction. The sails of a boat are things easier? attached to pulleys. A pulley has a wheel that turns on an axle. The sailors pull on a rope that wraps over the wheel of each pulley. This causes the sail to move in the proper direction. 22 23
VocabularyGlossary What did you learn? forceforce any push or pull 1. What is the difference between constant speed and variable speed? frictionfriction a force that goes against the gravity motion of an object 2. Would it take more force to begin moving gravity a non-contact force that pulls an empty wagon or a wagon loaded with magnetism pumpkins? Why? objects toward each other motion 3. What is the difference between a contact force magnetism a non-contact force that pulls on position and a non-contact force? Give examples of each. certain kinds of metal such as relative position iron 4. In this book you have motion a change in the position of read about work and simple machines. Write to speed explain how simple machines make work easier an object work without lessening the amount of work that gets position the location of an object done. Use examples from the book. relative position the position of one object 5. Summarize Turn to p. 11. Summarize the Photographs: Every effort has been made to secure permission and provide appropriate credit forcompared with the position of forces used when riding a bike. photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Unless otherwise acknowledged, all photographs are the property of Scottother objects Foresman, a division of Pearson Education. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R) Background (Bkgd) Opener: ©Allsport Photography/Getty Images; 2 ©David Young-Wolff/PhotoEdit; 4 ©Roy Ooms/speed how fast an object changes Masterfile Corporation; 5 ©John Elk/Bruce Coleman Inc.; 6 (TL) ©Richard Megna/Fundamental Photographs, (CR) ©Stone/Getty Images, (BL) ©Tom Szuba/Masterfile Corporation; 7 ©Kunst & Scheidulin/Age Fotostock; 8 ©Jim Cummins/Corbis; 10 ©Rolf Bruderer/Corbis; 11 ©Stone/Gettyits position Images; 12 ©Hennie Wiggers/Zefa/Masterfile Corporation; 14 ©Taxi/Getty Images; 15 AlaskaStock; 16 ©Bob Daemmrich/Corbis; 17 ©DK Images; 18 (CL) Getty Images, (R) ©Tony Freeman/PhotoEdit; 20 Corbis; 22 ©Keith Pritchard/Alamy Images; 23 ©Neil Rabinowitz/Corbis work when an object is moved by ISBN: 0-328-13841-X a force 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 permissions, 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 24
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