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Interactive textbook ยท Energy ยท Chapters 4 & 5

Light

Where light comes from, how it helps us see, and how shadows are formed and change. Shine torches, line up cards, move the ball and the screen, and follow your own shadow through the day. Your progress is saved on this device.

Light

Textbook pp. 82โ€“93 ยท Parts 1 to 4

MumGood night, Belle. I'm going to switch off the light now.

BelleGood night, Mum. Could you leave the light switched on? Without any light, I cannot find my slippers if I need to go to the bathroom in the middle of the night.

MumYes! That reminds me. I bought you a small night light. The light will not be too bright to disturb your sleep, but it will help you see the things around your room if you wake up in the middle of the night.

BelleThank you, Mum. Good night!

Think about itWhy would Belle trip over things in the dark, even in her own room?

Without light, she cannot see the things around her. Read on!

Part 1 ยท Textbook p. 82

Light helps us to see things

Light helps us to see things. Without light, the surroundings look dark and we cannot see the things around us. We will not be able to find things we need in the dark. We may trip over or knock against objects around us if we cannot see them. The presence of light helps us find things easily and avoid accidents.

What I Am Learning
  • Where does light come from?
  • How does light help us see things around us?
Try it ยท Belle's bedroom at night

Find the slippers in the dark

Belle needs her slippers, her water bottle, her book and her soft toy. Choose a light, then move your finger or mouse over the room. With the room light off, you can only see what the torch beam falls on. Find all four things.

Light in the room
Things found0 / 4

It is completely dark. Can you see anything at all?

Try it ยท Not too bright, not too dim

Set Belle's night light

Mum's night light should not be too bright to disturb Belle's sleep, but bright enough to help her see the things around her room. Turn the dial to find a brightness that does both.

Brightness0%
offdimvery bright
Can Belle see her room?
Can Belle sleep well?

The night light is off. Belle cannot see her slippers.

Try it ยท A walk to the bathroom

Avoid the accidents

Guide Belle ๐Ÿง’ from her bed to the bathroom door ๐Ÿšช. Toys and furniture are on the floor. With no light you only see the square you are standing on, so you may knock against things. Switch on the night light and walk again. Count the bumps.

You can also use the arrow keys after tapping the room.

Steps0
Bumps0

Belle is in bed. Which way is the door?

Try it ยท Do you need light for this?

In a completely dark room, can you stillโ€ฆ

Light helps us to see things. Sort each activity: can you still do it in total darkness, or do you need light to see?

๐Ÿ’ก Needs lightwe must see to do it

๐ŸŒ‘ Can do it in the darkwe use other senses

Remember

The presence of light helps us find things easily and avoid accidents. Without light, the surroundings look dark and we cannot see the things around us.

Answer the quick check to finish this part.

Part 2 ยท Textbook pp. 83โ€“85

Where does light come from?

Some objects give off light. We call these objects sources of light. Some sources of light are natural, while some are man-made.

Natural sources of light

Some objects can give off light naturally. We call these objects natural sources of light. Examples of natural sources of light are the Sun, stars and some living things. Some natural happenings, such as lightning, can also give off light.

โ˜€๏ธ The Sun

The main source of light on the Earth.

โœจ Stars

Other stars give off their own light too.

๐Ÿชฒ Living things

Some types of fireflies, jellyfish, deep-sea plants and glow-worms.

โšก Natural happenings

Lightning.

The Sun

The Sun is our main source of light.

The Sun, which is a star, is the main source of light on the Earth. During the day, light from the Sun helps us to see things around us.

Stars

Besides the Sun, there are other stars that give off their own light too. However, the amount of light that reaches the Earth is too little to brighten up our surroundings at night. Hence, we need other sources of light at night.

Try it ยท From sunrise to night

Who lights up our surroundings?

Drag the time of day. Watch the Sun cross the sky, then set. At night the stars come out. They give off their own light, but is it enough to brighten up the park? Switch on the street lamps to compare.

Time12 noon
midnightnoonmidnight
How bright is the park?โ€”
too dark to seebright

It is noon. Light from the Sun helps us to see things around us.

Living things

Some living things can produce their own light. Examples of these living things are some types of fireflies, jellyfish, deep-sea plants and glow-worms. Because they give off light, they can be seen by other animals at night or in the deep, dark sea.

Try it ยท Dive into the deep, dark sea

Who can be seen down here?

Dive deeper. Less and less sunlight reaches the water, until it is completely dark. Which living things can still be seen? Only the ones that give off their own light. (The depths are rough, to show the idea.)

Depth0 m
surface500 m1000 m
Sunlight reaching here100%
Can be seen

At the surface, sunlight lets us see every animal.

fireflyjellyfishdeep-sea plantglow-worms
Some types of fireflies, jellyfish, deep-sea plants and glow-worms give off their own light.
๐ŸŒ Science Around Us

Some types of fireflies also produce light in different patterns. These patterns can help fireflies recognise one another.

Light produced by fireflies

Try it ยท Be a firefly

Recognise the flash pattern

Each type of firefly in this game flashes its own pattern. Watch the mystery firefly in the dark, then pick the type that matches, just as fireflies recognise one another. (The three patterns are made up for the game.)

Which one is it?
Round1 / 5
Recognised0

Watch the flashing firefly carefully.

Natural happenings

Lightning is a flash of bright light in the sky. It usually happens during a thunderstorm. It is an example of natural happenings that give off their own light.

Try it ยท A thunderstorm at night

A flash of bright light

It is night and the city is dark. Press the button to start a flash of lightning. For a moment, the lightning lights up the whole sky and the buildings.

Flashes0
Sky nowdark

The city is dark. What gives off light in a thunderstorm?

Lightning seen in the night sky

Try it ยท Four kinds of natural sources

Sort the natural sources of light

Tap a card, then tap the box it belongs in. You can also drag the cards.

โ˜€๏ธ The Sunour main source

โœจ Starsother stars

๐Ÿชฒ Living thingsmake their own light

โšก Natural happeningsin nature

Answer the quick check to finish this part.

Part 3 ยท Textbook pp. 86โ€“87

Man-made sources of light

Some sources of light are made by man. Examples of these man-made sources of light are light bulbs and fireworks.

Try it ยท When the Sun has set

Switch on the table lamp

Set the time. When the Sun has set, there is no natural light coming in through the window. Switch on the table lamp and see what it does for the bedroom.

Light from
darkbright

During the day, light from the Sun comes in through the window.

A girl switching on a table lamp

These man-made sources of light brighten up our surroundings in the absence of natural sources of light.

Man-made sources of light such as fireworks can also be used to produce light displays during a celebration. Against the night sky, we can observe interesting patterns of light produced by the fireworks.

Try it ยท A celebration over the bay

Make a light display

Choose a pattern, then tap the night sky to launch a firework there. Against the dark sky, you can see the patterns of light clearly. Try the same firework in the daytime too.

Pattern
Launched0
Patterns tried0 / 4

Tap anywhere in the sky.

Fireworks lighting up the dark sky

๐Ÿ’ก I'm Inspired

The advancement of Science has allowed man to create different sources of light that we can use in our everyday life.

One example is the light bulb invented by Thomas Edison. Thomas Edison was the first person to create a type of light bulb that could be used in homes. The light bulbs invented by other scientists earlier were either too big or too bright for homes.

Due to his tireless search for a better design and his resilience in making a bulb that functions well, we now have light in our homes.

Thomas Edison

Try it ยท Design a bulb for a home

Keep trying, like Edison

Earlier light bulbs were either too big or too bright for homes. Change the design and test it. A good home bulb must be small enough for a room, not too bright, and must keep glowing for a long time. Every test is logged, so you can see how your resilience pays off. (A simplified model for the game.)

Size of the bulbHuge
hand-sizedhuge
BrightnessDazzling
gentledazzling
Glowing part
  • Small enough for a home
  • Not too bright for a home
  • Keeps glowing for a long time

Test the first design.

Light can come from natural and man-made sources of light.

Try it ยท Natural, man-made, or not a source at all?

Is it a source of light?

A source of light gives off its own light. Some things look bright only because light shines on them. Sort carefully!

๐ŸŒฟ Natural sourcegives off light naturally

๐Ÿ”ง Man-made sourcemade by man

๐Ÿšซ Not a sourcedoes not give off its own light

Textbook pp. 88โ€“89 were not in the scanned copy this lesson was built from, so they are not included here. The next part continues from p. 90.

Answer the quick check to finish this part.

Part 4 ยท Textbook pp. 90โ€“93

How do we see things that do not give off light?

Most of the things around us are not sources of light. Have you ever wondered how we can see things that do not give off their own light?

Oh dear! There's a blackout!

It's so dark! I cannot see anything around me.

Let me get the torch from the kitchen drawer.

BelleI wonder how the light from the torch allows us to see things inside the room.

Think about itThe sofa does not give off light. So how can Belle see it once the torch is on?

Light from the torch bounces off the sofaโ€ฆ

For us to see objects that do not give off their own light, a source of light has to be present. When light from the source of light shines onto an object, the light will bounce off the object. When this happens, we say that light is reflected. When the reflected light enters our eyes, we can see the object.

Try it ยท Follow the light

Belle and the pencil

Step through the picture. Light from the torch shines onto the pencil, then is reflected into Belle's eyes. Switch off the torch, or block the reflected light, and see what happens.

1. Light from the torch shines onto the pencil.
2. Light from the torch is reflected from the pencil into Belle's eyes.

Press play to send light from the torch.

Belle can see the pencil because light from the torch falls onto the pencil and is reflected into Belle's eyes.

Try it ยท Three scenes from the book

Which source of light is Belle using?

Pick a scene and a time of day. Switch the lamp on or off and open or close the curtains. Belle can only see the object when light from a source falls onto it and is reflected into her eyes.

Belle needs to switch on the lamp at night because the Sun is no longer the source of light. The light from the lamp falls onto the sofa and is reflected from the sofa. When the reflected light from the sofa enters Belle's eyes, she is able to see the sofa.

During the day, light from the Sun helps us see things around us.

Belle can see the sofa in her living room without switching on the lamp because sunlight enters through the window and falls onto the sofa. It is then reflected from the sofa and enters Belle's eyes.

Belle can see the swing during the day because sunlight is reflected from the swing and enters her eyes.

Try it ยท Torch in a blackout

Shine the torch around the room

Drag across the room to point the torch. Each object you light up reflects light. If the reflected light can reach Belle's eyes, she sees it and it is ticked off. The arrows show the path of the light.

Torch angle0ยฐ
Belle can see0 / 5

Point the torch at something.

Try it ยท In the right order

How does Belle see the sofa at night?

Tap the steps in order, from the first to the last.

  1.  
  2.  
  3.  
  4.  

What has to happen first?

๐ŸŒ Science Around Us

Did you know that the Moon does not produce its own light? Unlike the Sun, the Moon is not a source of light.

How then is it possible for us to see the Moon if it does not produce its own light?

We can see the Moon because the light from the Sun falls onto the Moon and is reflected into our eyes.

Try it ยท Sun, Moon and Earth

Why can we see the Moon?

Move the Moon around the Earth. Sunlight always lights up the half of the Moon facing the Sun, and that light is reflected to us on the Earth. Then try the "what if" switch: what would happen to the Moon if the Sun stopped giving off light? (A thought experiment, and the sizes and distances are not to scale.)

Moon's position0ยฐ
From the Earth we see

๐Ÿ’ป Let's Inquire
  • SLS: Light

We can see things around us either because they are sources of light or because they reflect light into our eyes.

Try it ยท Why can we see it?

Gives off light, or reflects light?

We can see each of these things. Sort them by the reason we can see them.

๐Ÿ”† It is a source of lightits light enters our eyes directly

โ†ฉ๏ธ It reflects lightinto our eyes

Try it ยท Myth or fact?

Clear up the mix-ups

Decide whether each sentence is a fact or a myth.

0 of 6 answered.

What I Have Learnt ยท Chapter 4
  1. Light can come from natural and man-made sources of light.
  2. We can see things around us either because they are sources of light or because they reflect light into our eyes.
Answer the quick check to finish this part.

Shadows

Textbook pp. 94โ€“119 ยท Parts 5 to 12

BoyGrandpa, when you were young, how did you watch shows if you didn't have a television?

GrandpaIn the past, we watched performances on a screen made of cloth. It is called wayang kulit.

BoyWhat is wayang kulit?

GrandpaIt is a traditional form of shadow puppet play.

BoyWhat are shadows and how are they formed?

It has to do with light being blocked. Keep reading!

You have learnt under Diversity of Materials in Primary 3 that light can only pass through some objects. You will learn how this property of light allows shadows to be formed.

What I Am Learning

Part 5 ยท Textbook pp. 95โ€“96

What are shadows?

An object that does not allow any light to pass through it is called an opaque object. An object that allows only some light to pass through it is called a translucent object. An object that allows most light to pass through it is called a transparent object.

๐Ÿชต Opaque

Does not allow any light to pass through it.

๐ŸŒซ Translucent

Allows only some light to pass through it.

๐ŸชŸ Transparent

Allows most light to pass through it.

Try it ยท The light tester

How much light gets through?

Pick a material and hold it in front of the torch. The light sensor on the right measures how much of the light passes through it. Test all ten materials. (The readings are typical values, rounded.)

Light passing throughโ€”
nonesomemost
So it isโ€”

Choose a material to test.

0 of 10 materials tested.

Try it ยท Sort the objects

Opaque, translucent or transparent?

Think about how much light each object lets through.

๐Ÿชต Opaqueno light passes through

๐ŸŒซ Translucentonly some light passes through

๐ŸชŸ Transparentmost light passes through

Do you know what happens when an opaque or a translucent object blocks light from falling onto a surface? Let us find out.

Try it ยท In the classroom

"Chen, you are blocking the light!"

The class is watching a video from the projector. Drag Chen across the room, or press the button to make him stand up in front of the projector. Then try holding up a sheet of tracing paper or a clear plastic file instead.

Chen's positionsitting
Blocking the light

Everyone can see the video.

When an opaque or a translucent object blocks light from falling onto a surface, dark areas are formed on the surface. These dark areas are called shadows.

Understanding how light interacts with objects to form shadows allows us to create interesting art such as shadow puppets.

Try it ยท Wayang kulit

Put on a shadow puppet play

The lamp is behind the cloth screen. Drag the puppet between the lamp and the screen. The audience on the other side sees its shadow. Make the puppet wave, and try a puppet made of a translucent material.

Drag the puppet into the light.

Shadows are dark areas formed on a surface when an opaque or a translucent object blocks light from falling onto a surface.

Try it ยท Shadow or not?

Is this dark area a shadow?

A shadow is formed only where an opaque or a translucent object blocks light from falling onto a surface. Decide for each picture.

0 of 6 answered.

Answer the quick check to finish this part.

Part 6 ยท Textbook pp. 97โ€“99

What are the properties of light that explain why a shadow is formed?

There are two properties of light that can explain why a shadow is formed:

Light travels in straight lines

Try it ยท A laser light show

Watch the beams

Aim the laser beams over the bay. Spray some mist into the air to make the beams easier to see. However you aim them, each beam is a straight line.

Aim0ยฐ
Mist in the airsome

Each beam goes from the laser in a straight line.

Light from a light show

Have you ever watched a laser light show? You may have noticed that the light from the source of light travels in straight lines. This shows that light travels in straight lines. We can test this out in a simple experiment.

How we can show that light travels in straight lines

Try it ยท Ali's experiment

Line up the holes

Slide cards A, B and C up or down on the base. Ali can see the lighted candle only when the light can travel through all three holes into his eye. Use "Move card B out of place" to repeat the book's test.

Card A0
Card B0
Card C0
โœ— Ali cannot see the light

The holes are not in a straight line yet.

When the three holes on cards A, B and C and the lighted candle are arranged in a straight line, Ali is able to see the light from the lighted candle through the holes. This means that the light from the lighted candle travels through the holes on the three cards into Ali's eye.

When card B is moved out of place, Ali is not able to see the light from the lighted candle. This means that the light from the lighted candle is blocked, as the hole on card B is out of line.

Ali is able to see the light from the lighted candle through the holes only when the holes are lined up. This shows that light travels in straight lines.

๐Ÿ” Let's Explore

Can you think of other ways to show that light travels in straight lines?

Try it ยท One more way

Look through a hose

Two children look at a lighted candle through a garden hose. Bend the hose and see whether the light still reaches their eyes.

Bend in the hosestraight
straightbent

The hose is straight. The child can see the candle flame.

Try it ยท Laser puzzle

Hit the light sensor

The laser beam travels in a straight line until it hits an object. Move the laser up or down and change its angle so that the beam reaches the sensor ๐ŸŽฏ without hitting a wooden block. The beam cannot bend around corners.

Level
Laser height0
Angle0ยฐ

Aim at the sensor.

โš ๏ธ Warning

Do not look directly at a source of bright light such as the Sun. The bright light can damage your eyes.

๐Ÿ’ป Let's Inquire
  • AB: Activity 5.1 (Part A)
  • SLS: Light Travels in Straight Lines
Answer the quick check to finish this part.

Part 7 ยท Textbook pp. 99โ€“101

Light cannot pass through an opaque object

Light travels in straight lines until it hits an object.

If light hits an opaque object, light will not be able to pass through it.

Since the wooden board is an opaque object, light cannot pass through it.

Try it ยท Torch, object, wall

Wooden board or frosted glass?

Shine the torch at the object in front of the wall. Compare the area on the wall behind each object.

Light on the wall behind0%
Area on the walldark

A dark area is formed on the wall because light cannot pass through the wooden board.

Only some light can pass through a translucent object

If light hits a translucent object, only some light will pass through it.

Since the frosted glass is a translucent object, it allows only some light to pass through it.

Light travels in straight lines.
Light cannot pass through an opaque object. Only some light can pass through a translucent object.

How are shadows formed?

You have learnt that light travels in straight lines. You have also learnt that an opaque object blocks light completely while a translucent object blocks light partially. When light is completely or partially blocked by an object, a shadow is formed.

๐Ÿ’ป Let's Inquire
  • AB: Activity 5.1 (Part B)
Try it ยท The lamp and the tabletop

Make a shadow on the tabletop

The tabletop becomes bright when light falls onto it. Hold a piece of cardboard, a frosted plastic sheet or a clear plastic sheet between the lamp and the tabletop. Drag it left and right, or change its height. Tap the tabletop to measure the light there.

Height above the table0 cm
Light under the sheetโ€”
Light beside itโ€”

This area remains bright

This area remains bright because light from the lamp falls onto it.

This area under the cardboard is dark

This area under the cardboard is dark because light from the lamp is blocked by the opaque piece of cardboard.

When a piece of cardboard is placed between the lamp and the tabletop, light that falls onto the opaque piece of cardboard cannot pass through it. Since no light falls onto the area of the tabletop below the cardboard, a shadow is formed on the tabletop.

When the piece of cardboard is replaced by a frosted plastic sheet, the shadow formed on the tabletop will be less dark. This is because some light is able to pass through the frosted plastic sheet.

Try it ยท From darkest to lightest

Rank the shadows

Each object is held under the same lamp. Tap them in order, from the one that forms the darkest shadow to the one that forms the lightest (or none at all).

  1.  
  2.  
  3.  
  4.  

Which object blocks light completely?

Try it ยท Explain it in steps

How is the shadow of the cardboard formed?

Put the explanation in order.

  1.  
  2.  
  3.  
  4.  

Where does the light start?

Shadows are formed when light is completely or partially blocked by an object.

๐Ÿ’ป Let's Inquire
  • SLS: Shadows
Answer the quick check to finish this part.

Part 8 ยท Textbook pp. 102โ€“107

What factors affect the size and shape of shadows formed?

โ–ฒ 8 a.m.      โ–ฒ 12 noon      โ–ฒ 4 p.m.

When you are outdoors, you may have noticed that the size and shape of the shadow of a tree formed are different at different times of the day. Do you know why?

Let us look at the factors that affect the size and shape of shadows.

What affects the size of shadows?

Shadows of different sizes can be formed by the same object. The size of a shadow depends on

The surface on which a shadow is formed is called the screen.

๐Ÿ’ป Let's Inquire
  • AB: Activity 5.2

How does the distance between the object and the source of light affect the size of the shadow?

As the source of light is placed further away from the object, the size of the shadow decreases. As the source of light is placed closer to the object, the size of the shadow increases.

Try it ยท Torch, ball and screen

Change one distance at a time

Choose what to move: the torch, the screen, or the ball. The light rays from the torch past the top and bottom of the ball show where the shadow reaches on the screen. Watch the size of the shadow change.

Torch position0 cm
Object to source of lightโ€”
Object to screenโ€”
Size of the shadowโ€”

Textbook

A shadow is formed on the screen when light travelling in straight lines is blocked by the ball.

Your record

Object to lightObject to screenShadow

torch ยท ball ยท screen

A shadow is formed on the screen when light travelling in straight lines is blocked by the ball.

Torch further away

When the torch is placed further away from the ball, the size of the shadow decreases.

Torch closer

When the torch is placed closer to the ball, the size of the shadow increases.

How does the distance between the object and the screen affect the size of the shadow?

As the screen is placed further away from the object, the size of the shadow increases. As the screen is placed closer to the object, the size of the shadow decreases.

Screen further away

When the screen is placed further away from the ball, the size of the shadow increases.

Screen closer

When the screen is placed closer to the ball, the size of the shadow decreases.

๐Ÿ” Let's Explore

GirlChen, have you ever wondered how the shadow of the ball will change if I move the ball instead of the torch or the screen?

ChenHmm... that is an interesting question. When we move the ball between the torch and the screen, the distance between the object and the source of light as well as the distance between the object and the screen change at the same time. Let's find out!

When the ball is placed closer to the torch, the ball is further away from the screen. Hence, the size of the shadow increases.

When the ball is placed further away from the torch, the ball is closer to the screen. Hence, the size of the shadow decreases.

ChenAs a conclusion to our investigation, we observe two things. First, as the object is placed closer to the source of light, the size of the shadow increases. Second, as the object is placed further away from the source of light, the size of the shadow decreases.

Try it ยท Predict, then test

Graph the shadow as the ball moves

The torch and the screen stay still, 100 cm apart. First choose the graph you think is right. Then move the ball from the torch to the screen and plot the real shadow sizes.

Ball from the torch20 cm

Make a prediction first.

0 of 9 points plotted.

๐Ÿ›  Let's Think and Do ยท Using and developing models

GirlChen, do you know another way to predict how the size of the shadow will change if the ball is moved between the source of light and the screen?

ChenYes, I know another way! We can draw light rays from the torch to the ball and the screen. Let's try it out!

To predict the size of the shadow of the ball, we can draw light rays from the torch past the top and bottom of the ball to show where these light rays will reach the screen.

Try it ยท Draw the light rays

Positions A, B and C

First predict: put the three positions in order, from the smallest shadow to the biggest. Then draw the light rays for each position by dragging from the torch past the top and the bottom of the ball. The bracket on the screen shows the size of the shadow.

My prediction: smallest โ†’ biggest shadow
smallest
middle
biggest

Make your prediction first.

By drawing light rays, we can predict that the shadow of the ball will be smaller when the ball is placed closer to the screen, and bigger when it is placed closer to the torch.

๐Ÿ’ป Let's Inquire
  • SLS: Sizes of Shadows
Try it ยท Puppet show problems

What would you change?

For each problem, pick every change that would work. More than one may be right.

0 of 3 solved.

Answer the quick check to finish this part.

Part 9 ยท Textbook p. 108

Our shadows through the day

๐ŸŒ Science Around Us

When we are outdoors on a clear, sunny day, we see our shadows on the ground. This is because our bodies block sunlight from reaching the ground.

Shadow formed on the ground

Have you noticed that the size, the shape and the position of your shadow change at different times of the day?

Early in the morning and late in the afternoon, the Sun is at its lowest position in the sky. Therefore, our shadows look very long. Nearer to noon, our shadows are the shortest, as the Sun is directly above us.

The shadow formed in the morning points in the opposite direction from the shadow formed in the evening. This is because the Sun rises in the East in the morning and sets in the West in the evening.

As the shadow changes in position and length throughout the day, people in ancient times used the changing shadow to tell time. They created a sundial, which showed the changing shadow of a rod at different times of the day.

Sundial

What do you think is the disadvantage of using a sundial to tell time?

Try it ยท Stand in the field all day

Your shadow from 7 a.m. to 6 p.m.

Drag the time. The Sun rises in the East and sets in the West. Watch the length and the direction of the boy's shadow, and record it in the table. The tracker draws a graph of the shadow's length. (A simplified model of a day near the equator, like in Singapore.)

โ† WestEast โ†’
Time8 a.m.
7 a.m.12 noon6 p.m.
Shadow lengthโ€”
Shadow pointsโ€”

TimeSunShadow lengthPoints
Try it ยท Tell the time with a shadow

Read the sundial

The rod on the sundial blocks sunlight and casts a shadow on the dial. Move the Sun and read the time. Then change the weather. When does the sundial stop working?

Real time10 a.m.
midnightnoonmidnight
The sundial showsโ€”
Shadow of the rodโ€”

The disadvantage of a sundial

A sundial needs sunlight. Its rod forms a shadow only when it blocks sunlight, so it cannot tell the time at night or when thick clouds block the Sun. (Our own answer to the textbook's question.)

Try it ยท From morning to evening

Put the five pictures in order

The textbook shows the boy's shadow at 8 a.m., 10 a.m., 12 noon, 2 p.m. and 4 p.m. Tap the shadows in order, starting with 8 a.m.

  1.  
  2.  
  3.  
  4.  
  5.  

Which shadow is formed at 8 a.m.?

๐Ÿ’ป Let's Inquire
  • AB: Activity 5.3
  • SLS: Positions and Lengths of Shadows
Answer the quick check to finish this part.

Part 10 ยท Textbook pp. 109โ€“112

What affects the shape of shadows?

The shape of an object determines the shape of its shadow.

Shadows of different shapes formed on a screen

A round object forms a round shadow.

๐Ÿ’ป Let's Inquire
  • AB: Activity 5.4

However, shadows of different shapes can also be formed by the same object.

The shape of the shadow depends on the part of the object that light shines onto.

Shadows of different shapes are formed when light shines onto different parts of a cone.

Try it ยท Turn the cone

One cone, different shadows

Turn the cone in the torch light, or pick one of the textbook's three views. Which part of the cone is the light shining onto? Watch the shadow on the screen.

Turn the cone90ยฐ
Light shines ontoโ€”
Shadowโ€”

โ–ผ Triangular

When light shines onto the triangular surface of the cone, the triangular surface will block the light from passing through it. Therefore, the shadow formed will be triangular.

โ— Circular

When light shines onto the circular surface of the cone, the circular surface will block the light from passing through it. Therefore, the shadow formed will be circular.

โ— Tip first

Even if the tip of the cone faces the source of light, the shadow formed will be circular. This is because the circular surface of the cone will block the light from passing through it.

AliBelle, what are you doing?

BelleHi, Ali. I am trying to make a bird-shaped shadow with my hands. While the shape of my hands looks like a bird, the shape of the shadow does not.

AliWhy don't you try turning your hands so that the shape you want faces the light shining onto your hands?

BelleIt works! Thanks, Ali.

Try it ยท Belle's bird

Turn your hands to the light

Belle's hands make a bird shape. Turn her hands. Only when the bird shape faces the light does the shadow on the wall look like a bird. Then try the other hand shadows.

Turn the hands80ยฐ
facing the lightside-on
Does the shadow look like it?

๐Ÿ’ป Let's Inquire
  • AB: Activity 5.5
  • SLS: Shapes of Shadows
Try it ยท The shadow lab

Shine light onto different parts of a solid

Pick a solid object, then turn it. The lamp shines from directly above, so the shadow on the floor shows the part of the object that the light shines onto. Drag on the picture to spin the object.

Tip it over0ยฐ
Spin it0ยฐ

Shadow shapes found: none yet.

Try it ยท Shadow detective

Which objects could make this shadow?

Select every object that could form the shadow, if it is turned the right way. Then check.

Case 1 of 4.

๐ŸŒ Science Around Us

Did you know that the Science behind shadows has been used by artists to produce interesting pieces of art? Artists construct objects and place them at a distance from different sources of light to create interesting shadows.

An example of shadow art

Try it ยท Be a shadow artist

A pile of junkโ€ฆ or a city?

The sculpture looks like a messy pile of objects. Turn it and move the lamp. At just the right angle, its shadow shows a city skyline. Then move the lamp closer or further to change the size of the shadow art.

Turn the sculpture0ยฐ
Lamp distancenear
Match with the skyline0%

Turn the sculpture slowly.

The size of a shadow depends on the distance between the object and the source of light, and the distance between the object and the screen.

The shape of a shadow depends on the part of the object that light shines onto.

Answer the quick check to finish this part.

Part 11 ยท Textbook pp. 113โ€“116

Let's Apply

These are the four questions at the end of the Shadows chapter. Choose or write an answer to see whether you are right and why. After each one, you can test your answer in a model.

Test your answers in a model

Model ยท Question 2

Ahmad's two wooden pieces

Square piece A (4 cm by 4 cm) and round piece B (4 cm across) stand between the source of light and the screen, with A nearer to the light. Slide them and watch the screen. When is the circle hidden inside the square's shadow?

Piece A from the light20 cm
Piece B from the light60 cm
Shadow of Aโ€”
Shadow of Bโ€”

Model ยท Question 4

Belle walks under the lamp

Press play to walk Belle from A to C, then back to B, or drag her yourself. The graph draws the length of her shadow over time. Compare it with the four graphs in question 4.

Belle's positionA
B sideAC side
Shadow lengthโ€”
Distance from Aโ€”

Your score
0 / 4

Answer all four questions.

โž• More practice from Polymath (not in the textbook)

Ten more questions on light and shadows, in the style of school tests. They do not count towards this part.

0 of 10 answered.

Part 12 ยท Textbook pp. 93, 117โ€“119

What I Have Learnt

Chapter 4 ยท Light

  1. Light can come from natural and man-made sources of light.
  2. We can see things around us either because they are sources of light or because they reflect light into our eyes.

Chapter 5 ยท Shadows

  1. Shadows are dark areas formed on a surface when an opaque or a translucent object blocks light from falling onto a surface.
  2. The following properties of light explain why shadows are formed:
    a. Light travels in straight lines.
    b. Light cannot pass through an opaque object. Only some light can pass through a translucent object.
  3. Shadows are formed when light is completely or partially blocked by an object.
  4. a. The size of a shadow depends on
    โ€ข the distance between the object and the source of light, and
    โ€ข the distance between the object and the screen.
    b. The shape of a shadow depends on the part of the object that light shines onto.

In the topic of Energy Forms and Uses (Light), you have learnt:

Try it ยท Complete the concept map (1 of 2)

Light: a form of energy, and its sources

Tap an empty box, then tap the word that belongs there. Every box should match the textbook's concept map.

Tap an empty box to begin.

Try it ยท Complete the concept map (2 of 2)

The function and properties of light

This half of the map shows how light helps us see, and how its properties result in shadows. Fill in every empty box.

Tap an empty box to begin.

Keep going!

Finish every part to complete the topic.

Back to all topics