3 12 forces and motion (physical science)

force friction gravity magnetism motion position relative position speed work What did you learn?. Relative position is the position of one object compared with the position of other

by Ann J Jacobs

Scott Foresman Science 3.12

Genre Comprehension Skill Text Features Science Content

Nonfi ction Summarize • Captions

• Chart

• Glossary

Forces in Motion

ISBN 0-328-13841-X

ì<(sk$m)=bdiebi< +^-Ä-U-Ä-U

Physical Science

by Ann J Jacobs

Scott Foresman Science 3.12

Genre Comprehension Skill Text Features Science Content

Nonfi ction Summarize • Captions

• Chart

• Glossary

Forces in Motion

ISBN 0-328-13841-X

ì<(sk$m)=bdiebi< +^-Ä-U-Ä-U

Physical Science

force

friction

gravity

magnetism

motion

position

relative position

speed

work

What did you learn?

1 What is the difference between constant speed

and variable speed?

2 Would it take more force to begin moving

an empty wagon or a wagon loaded with pumpkins? Why?

3 What is the difference between a contact force

and a non-contact force? Give examples of each

read about work and simple machines Write to explain how simple machines make work easier without lessening the amount of work that gets done Use examples from the book

5 Summarize Turn to p 11 Summarize the

forces used when riding a bike

Photographs: Every 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 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

Forces and Motion

by Ann J Jacobs

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

3

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

Positions of Moving Objects

When one thing depends on another thing

for its meaning, we say it is relative Relative

position is the position of one object compared

with the position of other objects Look at car 64

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

Look at the train below The locomotive is in front

Two cars are being pulled behind it Could the cars move in front of the locomotive? They could if the train started moving backward Relative position can change if objects start moving in a new direction

5

How Fast Things Move

Speed is how fast an object changes its position

Speed can be fast A jet plane moves fast Speed can

be slow Honey moves slowly Some things have such a

slow speed that you can’t see them move!

The arms of a tuning fork move very fast.

Honey moves at

a slow speed.

The motion of these flowers is too slow to see.

7

Constant Speed

Objects can move at a constant speed This means that they do not change how fast or slow they move

They are always changing position The rate at which they change position stays the same

Variable Speed

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

How does force

affect motion?

The Causes of Motion

A force is any push or

pull A force can change

an object’s position It can

change the direction of an

object’s motion too

Most forces you use are

contact forces To push or

pull an object, you must

touch it A bat makes contact

with a ball to move it

The more force you use,

the more an object’s motion

changes The harder you

push on a cart, the faster

it goes!

More force is needed

to push three carts than to push just one

9

The mass of an object affects how it moves You don’t need much force to begin pushing an empty cart When the cart is full of food, it has more mass

Now more force is needed to begin moving the cart

As the cart moves, its wheels rub against the floor

This causes friction Friction is a contact force that

slows an object’s motion Smooth surfaces produce less friction than rough ones Friction is helpful when you want to slow something down

Motion and Combined Forces

You know that pushes, pulls, and friction can

change an object’s motion Now think about the

forces in tug-of-war Your team’s pull is a force in

one direction The other team’s pull is a force in the

other direction If the forces are the same, the rope

doesn’t move

Suppose everyone on your team pulls together to

move the rope The rope will move in your direction if

you have the stronger force So get more friends to help!

Lots of forces cause a bike to change its motion

You push on the pedals You push on the handlebars and shift your weight to turn Friction between the tires and the ground slows your forward motion

Going up hills takes more force You may gain too much speed going down hills You pull on the brakes

to slow down All these forces work together to keep your bike moving

11

Gravity and Magnetism

A non-contact force is a push or pull that affects an

object without touching it Gravity is a non-contact

force that pulls objects toward each other Gravity

pulls everything on Earth toward Earth’s center

Weight is the amount that gravity pulls on an

object Objects weigh less on the Moon because the

Moon has less gravity than Earth The pull of gravity

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

Gravity pulls skydivers

toward the ground.

13

The pull of gravity also depends on matter Objects with more matter have more mass The more mass, the stronger the pull of gravity

Magnetism is another non-contact force Magnets

pull on objects with certain kinds of metal such as iron

in them You might use a magnet to pull a steel paper clip across your desk Steel is a metal with iron in it

Magnets do not affect objects that lack these metals

This magnet does not attract crayons since they lack metal the magnet can attract

This magnet attracts paper clips because they have iron.

Activity Work When Work Is Done

Thinking about a math problem Turning a jump rope Holding a puppy Lifting a puppy Pulling on a locked door Opening an unlocked door Trying to scoop rock-hard ice cream

No Yes No Yes No Yes No 14

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

15

How much work do you do in a day? To find out, you would have to keep track of all the pushing and pulling you do Then you would have to see how far those pushes and pulls moved things

Putting a book on a shelf is work What if you put the book on a shelf twice as high? You would do twice

as much work! You would also do twice as much work

if you put a book that weighed twice as much on the lower shelf

Some Simple Machines

Machines can’t reduce the amount of work that

needs to be done But they can help make your work

easier Here are six kinds of simple machines

Inclined Plane

Look at the man pushing the cart below Without

the ramp, the man would have to lift the cart into the

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

Wedge

A wedge is a simple machine It is used to split, cut, or fasten things A wedge has one or two slanted sides that form a sharp edge A

wedge can move through material and separate it A knife is a wedge that can cut a pie An axe head is a wedge that can split wood

Screw

A screw is an inclined plane wrapped around a

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

19

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!

Support

More Simple Machines

Wheel and Axle

Whenever you open a door, you use a simple

machine It is called a wheel and axle The doorknob

is a wheel The post that attaches to its center is an

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

The rides you see below both use a big wheel and axle Instead of turning the wheel, a motor in these rides turns the axle The motor turns the axle

a small distance But the distance the axle turns the wheel is great This makes the ride fun The motor must put a great force on the axle to do this

21

Do you think the people on this ride are having fun?

Pulley

Pulleys are simple machines that can help move

things in the right direction The sails of a boat are

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

You live in a world of motion Look around What

is moving quickly? What is moving slowly? What simple machines will you use today to make moving things easier?

Glossary

force any push or pull

friction a force that goes against the

motion of an object

gravity a non-contact force that pulls

objects toward each other

magnetism a non-contact force that pulls on

certain kinds of metal such as iron

motion a change in the position of

an object

position the location of an object

relative position the position of one object

compared with the position of other objects

speed how fast an object changes

its position

work when an object is moved by

a force

Vocabulary

force

friction

gravity

magnetism

motion

position

relative position

speed

work

What did you learn?

1 What is the difference between constant speed

and variable speed?

2 Would it take more force to begin moving

an empty wagon or a wagon loaded with pumpkins? Why?

3 What is the difference between a contact force

and a non-contact force? Give examples of each

read about work and simple machines Write to explain how simple machines make work easier without lessening the amount of work that gets done Use examples from the book

5 Summarize Turn to p 11 Summarize the

forces used when riding a bike

Photographs: Every 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 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