Page 2
Copyright © by Harcourt, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Requests for permission to make copies of any part of the work should be addressed to School Permissions and Copyrights, Harcourt, Inc., 6277 Sea Harbor Drive, Orlando, Florida 32887-6777. Fax: 407-345-2418. HARCOURT and the Harcourt Logo are trademarks of Harcourt, Inc., registered in the United States of America and/or other jurisdictions. Printed in Mexico ISBN-13: 978-0-15-352338-0 ISBN-10: 0-15-352338-7 1 2 3 4 5 6 7 8 9 10 050 15 14 13 12 11 10 09 08 07 06 If you have received these materials as examination copies free of charge, Harcourt School Publishers retains title to the materials and they may not be resold. Resale of examination copies is strictly prohibited and is illegal. Possession of this publication in print format does not entitle users to convert this publication, or any portion of it, into electronic format.
Page 3
Faster Than a Speeding Bullet . . . . . . . . . . . . . . . . . . .2 Every Color of the Rainbow . . . . . . . . . . . . . . . . . . . . .4 Bounce Off or Take In?. . . . . . . . . . . . . . . . . . . . . . . . .6 Seeing Things in a Different Light. . . . . . . . . . . . . . . .8 Red, Blue and Green, Oh My! . . . . . . . . . . . . . . . . . . 10 Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 Visit The Learning Site! www.harcourtschool.com
Page 4
Faster Than a Speeding Bullet Can you raise a window shade in the morning and then try to grab something in the room before light hits it? Of course, you can’t! Actually, no one can. Light is the fastest thing we know of—far faster than even a speeding bullet. In a vacuum, light travels just under 300,000 kilometers (186,000 mi)each second. That’s fast! There is a way you can “beat” sunlight: pull the shade down again. Most shades are opaque—meaning light can’t pass through them—so the room will stay dark. The room would be brighter if you used a translucent curtain. That would let in some light. It would be brighter still if you didn’t use anything to cover the transparent glass in the window. It would let nearly all the light pass through. White curtains are translucent. They let only some light pass through. You can’t see through them clearly. 22
Page 5
Part of the room would still be dark, though, if you stood in front of the window. Light travels in straight lines. It can’t go through or around you. That’s why your body would cast a shadow. A shadow is a dark area that forms where an object blocks light. Shadows can move and change. Suppose you raised your arms as you stood in front of the window. Your body would block different lines of light. This would cause the shape of your shadow to change. Now suppose you’re outside in the sun. Your shadow changes as the sun’s position in the sky changes. In early morning or late afternoon, the sun is low in the sky. Your shadow is long. At noon, the sun is directly overhead. Your shadow is small and close to your feet. MAIN IDEA AND DETAILS What is a shadow? What makes a shadow change? 33
Page 6
Every Color of the Rainbow Imagine a world without color. How boring! Luckily, our world is full of color, from the deepest red to the palest blue. Sunlight contains many colors, too. You may not have realized this, because sunlight looks white. However, you can see the colors in sunlight by using a prism. Light bends as it passes through a prism. Violet bends the most. Red bends the least. The bending is what causes the colors to separate. white light prism 44
Page 7
When a tight beam of white light Ever wonder why the sun passes through a appears redder at sunrise and glass prism, its sunset? This is because dust and other particles in Earth’s different colors bend atmosphere. These particles by different scatter blue light more than red amounts. This light. At sunrise and sunset, the sun’s light travels much farther bending produces a through Earth’s atmosphere. spectrum, or range, With much more blue scattered out of the sunlight, the red light of colors. They appears brighter. include red, orange, yellow, green, blue, violet—and millions of shades in between. Other things can act like prisms and bend light, too. When water droplets in the air bend light, this same range of colors forms a rainbow across the sky. CAUSE AND EFFECT What causes the colors that we see when white light passes through a prism? 5
Page 8
Bounce Off or Take In? When light strikes an object, some of it may reflect from the object, or bounce off. You see the object because the reflected light enters your eyes. A smooth, shiny surface—such as a mirror— reflects light in a way that allows you to see your own image. This image is your reflection. Most objects or surfaces are not as smooth and shiny as mirrors. Light that is reflected from surfaces that are rough or dull is reflected in many different directions. This is why you don’t see your image when you look at a rock or a tree! Light bounces off a mirror and forms an image. The image in a flat mirror is always upright, life-sized, and reversed from left to right. 6
Page 9
An object may also absorb, or take in, some of the light that strikes it. The light that is not absorbed by the object is reflected. Objects of different colors reflect different colors of light. In white light, bananas reflect yellow light and absorb light of all other colors. Green apples reflect green light and absorb all other colors of light. The reflected light travels to our eyes, allowing us to see the colors of these objects. We see yellow for bananas and green for green apples. Color really is in the eye of the beholder! The skin of the bananas absorbs all colors of light except yellow. The apple reflects green light but takes in all other colors. COMPARE AND CONTRAST Explain the differences between reflection and absorption of light. 7
Page 10
Seeing Things in a Different Light In white light, a lime looks green. What color will it seem to be if the light that shines on it is not white? The color we see depends on the color of light that shines on an object. If you shine blue light on a lime, it will look black. That’s because the lime absorbs all of the blue light. There is no green light for the lime to reflect. In white light, the petals of the rose reflect red light, and the leaves reflect green light. In blue light, neither the petals nor the leaves are their true colors. 8
Page 11
Three things affect color. The first is the colors of light an object reflects or absorbs. The second is the color of light that strikes an object. The third is how your eyes respond to light. If any one of these things changes, an object’s color will change. CAUSE AND EFFECT Why does a lemon look black when it is seen in blue light? In red light, the petals look red, but the leaves look black because there is no green light for them to reflect. In green light, the leaves look green, but the petals look black because there is no red light for them to reflect. 9
Page 12
Red, Blue and Green Oh My! How do you see? Light enters your eye through the pupil. This is the dark area in the center or each eye. The iris is the colored part that surrounds the pupil. The iris contains two kinds of muscles that work together to change the size of the pupil. In dim light, the iris makes the pupil large so that more light can enter the eye. In bright light, the iris makes the pupil small so that only a little light can get through. Light is all around you. You see objects because light bounces off them and travels to your eyes. 10
Page 13
First, light passes through the pupil. Next, the light passes through the lens. The lens bends the light to Last, a nerve focus on the retina, at carries information the back of the eye. from the retina to the brain. Like a camera, the eye has a lens that focuses light. The lens focuses the light on a certain area of the retina, which surrounds the back of the eye. The retina contains tiny parts called cones. There are three kinds of cones. Each kind In addition to cones, the retina contains tiny parts senses either red light, green called rods. Rods do not light, or blue light. The retina sense color. Instead, they help us see in dim light sends information to the and sense movement. brain through a nerve. The There are about 20 times brain tells us what we see. as many rods in the eye as there are cones. MAIN IDEA AND DETAILS Explain how each part of the eye helps us see objects. 11
Page 14
Glossary absorb (ab•SAWRB) To take in (7, 11) opaque (oh•PAYK) Not able to let light pass through (2, 11) reflect (rih•FLEKT) To bounce off a surface (6, 7, 11) shadow (SHAD•oh) A dark area that forms where and object blocks the path of light (6, 11) translucent (trans•LOO•suhnt) Lets some light pass through (6, 11) transparent (trans•PAIR•uhnt) Lets most light pass through (6, 11) 12
Page 15
Think and Write 1. How do we know that sunlight contains more than one color? 2. COMPARE AND CONTRAST Explain the differences between opaque, translucent, and transparent objects. 3. CAUSE AND EFFECT Think about a red rose. In white light, the stem and leaves of the rose look green. The petals look red. Explain why we see these colors. 4. Expository Writing Write a paragraph that explains why you see your reflection when you look at some surfaces and not when you look at others. Hands-On Activity With a partner, identify every color you see during a 10-minute period. Write the name of each color on an index card. Use as many names for colors as you know. Group the cards according to the main color each is closest to: red, orange, yellow, green, blue, or violet. School-Home Connection Walk around your home with a family member. Classify each object you see as opaque, translucent, or transparent. Shine a flashlight on each object to make sure you are correct.
Page 16
Catch the Waves Light is a form of energy that we can see. Not every person can see every color of light. This is often called colorblindness. Most colorblind people actually can see colors. They have trouble, though, telling the difference between some colors, such as red and green. Even people with the best color vision can see only the colors between red and violet. Some animals, though, can see other colors of light. Bees, for example, can see ultraviolet light. Some snakes can see infrared light. Birds have at least four kinds of cones in their retinas. This means that they can see more shades of color than people can. Compared with these animals, we’re all colorblind! COMPARE AND CONTRAST Tell how people see colors differently than bees and some snakes do. These are just pretty flowers to us, but to bees, the dark area in the center of each flower is a giant bull’s-eye saying “free Food!” d What humans see What bees see
Page 17
Summary Light is the fastest thing there is. It travels in straight lines. Objects that light can’t pass through are opaque. Translucent objects let some light pass through, and transparent objects let most light pass through. When something blocks light, it forms a shadow. White light is a mixture of colors. As white light passes through a prism, the different colors are separated because each is bent by a different amount. We see the colors that are reflected from objects, or bounce off. The colors that don’t bounce off are absorbed. We see objects when light from the objects travels to our eyes. Light moves through the pupil. Then it is bent by the lens so that it falls on a certain part of the retina. From the retina, a nerve carries information to the brain. Some animals can see types of light that people can’t see. e
Affichage des 17 premières pages. Téléchargez le document pour le voir en entier.
Commentaires (0)
Aucun commentaire pour le moment. Soyez le premier !