New: for practice that adapts to you, open the Physical Science Explorer. ✓ Tick the box under each page when you have finished it. Your ticks are saved for next time. ▶ Watch It pages are animated lessons with step-by-step captions. Every diagram with a ↻ replay button moves. Tap Show answer on Check Yourself pages to test yourself.
My Progress
Tick each page when you finish it. Fill every bar to earn all the stars!
Five core topics from the MOE Primary Science syllabus, explained step by step. Spot the tricky questions, learn to write model answers and check yourself at the end of every chapter.
Clear explanationsTricky questions explainedModel answersAnimated online version
Diversity of Materials
Magnets
Matter
Light and Shadows
Heat
Written by [Author Name]Follows the MOE 2023 Primary Science syllabus[Publisher]
SCIENCE MADE CLEAR
How to Use This Book
A short note from Professor Pip
Hello, young scientist!I am Professor Pip. I will pop up with questions, tips and trap alerts. Read one chapter at a time, then test yourself.
A Study Plan
Read the Core Idea out loud.
Work through the How It Works pages. Say each diagram in your own words.
Cover the Right Idea column on the Mark Savers page and test yourself.
Practise one Model Answers question without looking.
Do Check Yourself and colour your stars.
Science Made Clear · Physical Science P3–4 · First edition Free edition, shared under CC BY-NC 4.0. Content is aligned to the MOE 2023 Primary Science syllabus (Primary 3 and 4).
What You Will Find in Each Chapter
Core IdeaThe one big idea of the chapter, in one sentence.
Pip Wonders...A puzzle to get you thinking before you start.
Where You See ItPlaces in Singapore where you can see the topic.
At a GlanceThe whole chapter in one small map.
How It WorksClear diagrams and tables that explain the science.
Experiments You Must KnowThe investigations you must know: what to do, see and conclude.
Mark SaversWrong ideas that cost marks, and the right ideas to write.
Model AnswersModel answers using the C-S-E Chain, then Your Turn to practise.
★ Did You Know?Amazing facts to share at dinner.
Try It at HomeA safe mini challenge. Ask an adult first.
In Real LifeWhere you can spot the science in Singapore.
Check YourselfQuick questions. Answers are at the back of the book.
▶ Watch ItAnimated lessons, in the interactive version only.
I can...Rate yourself with stars at the end of each chapter.
Pip's notesTips, memory tricks, puzzles and trap alerts from Pip.
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How to Use This Book
SCIENCE MADE CLEAR
The C-S-E Chain
How to answer open-ended questions
Many Science questions ask you to explain. Strong answers link three ideas together like a chain. If one link is missing, you lose marks.
Cause
What changed, or what is different? Start from what the question tells you.
→
Science
What happens, using the correct science keyword? This is the link most pupils forget.
→
Effect
What is the result? Link it back to the exact question.
Worked example
Wei Jie stirred his hot soup with a metal spoon. After a while, the handle of the spoon felt hot. Explain why.
CauseThe spoon was placed in the hot soup.ScienceMetal is a good conductor of heat. The spoon gained heat from the hotter soup, and the heat travelled along the spoon.EffectThe handle became hotter, so it felt hot.
✕ Loses marks: "Because the soup is hot." It gives the cause but no science and no link to the handle.
Four Habits of Top Scorers
Underline what the question asks: explain, compare, suggest or state.
Use the exact keyword: "good conductor of heat", "takes up space", "like poles repel".
Talk about the thing in the question, such as "the spoon", not "it".
Finish by answering the question that was asked.
Spot the Missing Link
Question: Why did the ice cube in Siti's hand melt?
Answer A: "Her hand is warm, so the ice melted." Missing: Science. Which way did the heat flow?
Answer B: "The ice gained heat from her warmer hand, so it melted into water." All three links!
Pip's promiseEvery chapter has three C‑S‑E model answers. Practise them and explaining will feel easy!
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Pip's QuestFinish a chapter, colour its stars, then tick it here: 1 ☐ 2 ☐ 3 ☐ 4 ☐ 5 ☐ Five ticks makes you a Physical Science Champion! Answers are on page 48.
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What Is Inside
SCIENCE MADE CLEAR
1
Materials
Materials
Core Idea: we choose a material because its properties suit the job.
strongflexiblewaterprooffloats or sinkslets light through
Core Idea
Every object is made of materials. Each material has its own properties: what it is like and what it can do. Know these seven:
Wooddoors, chairs
Metalspoons, pots
Ceramicbowls, tiles
Rubbertyres, erasers
Glasswindows, jars
Plasticbottles, boxes
Fabricclothes, bags
TipOne object can use many materials!
The job needs a property → pick the material that has it
Why should I care? exams often ask why an object is made of a material. Answer with a property linked to the use.
Where You See It
Bus stop Your umbrella keeps you dry because its cloth is waterproof.
MRT train Windows are glass, so light passes through and you can see out.
Hawker centre Bowls are ceramic: strong, waterproof and easy to wash.
School Your bag is fabric: strong enough for books, flexible enough to fold.
Pip Wonders...Why do we not make umbrellas out of paper, or windows out of wood? See The Right Material!
At a Glance
Strength holds a load without breaking
Flexibility bends without breaking
Floats / sinks stays up or goes down in water
Waterproof lets no water through
Light lets most, some or no light through
5SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
SCIENCE MADE CLEAR
1
Materials
Meet the Materials
How It Works: each material has its own properties
Wood
✓ strong, most wood floats✕ lets no light through✕ absorbs some water, so outdoor wood is painted or varnished
Used for: doors, tables, chopsticks, boats Spot it chopsticks at the hawker centre
Metal
✓ very strong, waterproof, shiny✓ thin metal (foil, wire) can bend✕ a solid lump of metal sinks; lets no light through
Used for: spoons, pots, keys, MRT tracks Spot it MRT tracks and lamp posts
Ceramic
✓ hard, holds a heavy load; waterproof (glazed)✕ not flexible: breaks easily if dropped✕ lets no light through; sinks
Used for: plates, bowls, floor tiles, toilet bowls Spot it tiles in HDB bathrooms
Rubber
✓ very flexible: bends and stretches✓ waterproof, grips well✕ lets no light through
Used for: tyres, erasers, rain boots, rubber bands Spot it tyres on SBS buses
Glass
✓ lets most light through (clear glass)✓ waterproof✕ not flexible: it breaks easily; sinks
Used for: windows, jars, spectacle lenses Spot it MRT platform screen doors
Plastic
✓ waterproof, light to carry✓ can be flexible (bags) or stiff (chairs)✓ some plastics let light through, some do not
Used for: bottles, raincoats, food boxes Spot it bubble tea cups
Fabric
✓ flexible and soft✓ can be strong (school bags)✕ cotton absorbs water; some fabrics are coated to be waterproof
Used for: clothes, bags, towels, umbrellas Spot it your school uniform
Did You Know?
Natural rubber comes from the milky sap of the rubber tree. Over 100 years ago, the Singapore Botanic Gardens helped to start rubber farming in Southeast Asia!
Glass is made mostly from sand, heated until it melts. The sand on a beach could become a window one day!
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Meet the Materials
SCIENCE MADE CLEAR
1
Materials
Property Detective
How It Works: five properties and how to test each one
Strength
Holds a heavy load without breaking.Detective test: hang a load on it. Will it break?Strong: metal, wood
Flexibility
Can bend without breaking.Detective test: bend it gently. Does it bend or snap?Flexible: rubber, fabric, thin plastic
Floats or Sinks
Floats: stays on or near the surface. Sinks: goes to the bottom.Detective test: put it gently in water. Up or down?Floats: most wood. Sinks: metal key, glass marble
Waterproof
Does not absorb water. Water does not soak in.Detective test: drip water on it. Does it soak in?Waterproof: plastic, rubber, glass, metal
Lets Light Through
Lets most, some or no light pass through.Detective test: shine a torch at it. Does light come out the other side?Most: clear glass. None: wood, metal
Light Through Materials
The more light a material lets through, the brighter the screen. Frosted bathroom windows let some light in, but no one can see clearly through them.
Pip's Silly Inventions
A paper umbrellaPaper absorbs water. Soggy in seconds!
A jelly chairJelly is not strong. Sit on it and... splat!
A glass trampolineGlass is not flexible. It would crack, not bounce.
A metal raftA solid metal block sinks. Glug, glug!
Each fails: the material has the wrong property for the job.
Pip's memory trickStrong = does not break. Flexible = can bend.
7SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
Property Detective
SCIENCE MADE CLEAR
1
Materials
Watch It
A fair strength test, step by step
1Which material makes the strongest strip? We test paper, cardboard and plastic.
2Keep it fair: same length, width and thickness, hung the same way. Change only the material.
3Hang one 50 g mass at a time from the middle of each strip.
4Paper breaks after 2 masses. Cardboard breaks after 6. Count and record each result.
5Careful! Plastic bends a lot, but it has not broken. Strong means holding a load without breaking.
6Result: plastic held the most masses (9), so it is the strongest strip in this test.
▶SCIENCE MADE CLEARWatch It · animated lesson
▶ Watch It: A fair strength test, step by step
SCIENCE MADE CLEAR
1
Materials
The Right Material
How It Works: job → property → material
Match the Job
Object
Property it needs
Good material
Raincoat
waterproof, flexible
plastic
Window
lets most light through
glass
Bicycle tyre
flexible, waterproof
rubber
Bookshelf
strong
wood or metal
Raft
floats, strong
wood
Towel
absorbs water, flexible
fabric (cotton)
Bathroom tiles
waterproof, strong
ceramic
Spectacle lenses
lets most light through
glass or plastic
Rubber boots
waterproof, flexible
rubber
A towel is a job where we want a material that absorbs water!
Bend Test
The plastic ruler bends and springs back: it is flexible. The wooden stick breaks when bent: it is not flexible, even though wood is strong.
Note: this is a quick demo, not a fair test. The ruler and the stick are different sizes and shapes.
Flexible things you use:
rubber bandplastic bagclothhosethin wire
Why Not?
An umbrella made of paper?Paper absorbs water. The rain would soak through and the paper would tear.
A school bag made of glass?Glass is not flexible and breaks easily. The bag would shatter if dropped.
A window made of wood?Wood lets no light through. The room would be dark and you could not see out.
A towel made of plastic?Plastic does not absorb water, so it could not dry your body.
8SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
The Right Material
SCIENCE MADE CLEAR
1
Materials
Watch It
Pick the best umbrella material
1Pip wants to make an umbrella canopy. It must be waterproof and flexible. Four materials are tested.
2Water test: drip water on each one. Paper and cotton absorb water, so they are not waterproof.
3Careful! Glass did not absorb water. So is glass the best choice? Being waterproof is only half the job.
4Bend test: plastic bends and springs back. Glass cracks, because it is not flexible.
5Answer: plastic is waterproof and flexible, so it is a good material for an umbrella canopy.
▶SCIENCE MADE CLEARWatch It · animated lesson
▶ Watch It: Pick the best umbrella material
SCIENCE MADE CLEAR
1
Materials
Experiments You Must Know
Testing materials fairly
Fair Test
Change ONE thingthe type of material
Keep the rest the SAMEsize, shape, thickness of each sample, how you test it
Measure ONE thinge.g. number of masses held, drops absorbed
1 · Which Is Strongest?
DoHang masses on strips of different materials, one at a time.MeasureCount the masses each strip holds before it breaks.SoThe strip that holds the most masses is the strongest.
Keep the same: size and thickness of each strip, and the masses used.
In real life Library shelves are made of strong materials so they do not break under heavy books.
2 · Which Is Waterproof?
DoDrop the same number of water drops on each sample.SeeOn plastic, the water stays as a drop. On cotton, it soaks in.SoPlastic does not let water pass through: it is waterproof.
Keep the same: sample size, number of drops, height of the dropper.
In real life Tents and raincoats are made of waterproof materials to keep campers dry.
3 · Float or Sink?
DoGently place each object in a tank of water.SeeThe wooden block floats. The metal key sinks.SoWe record whether each object floats or sinks; we do not guess by its size.
In real life A life jacket is made of materials that float, so it keeps you up in the water.
9SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
Experiments You Must Know
SCIENCE MADE CLEAR
1
Materials
Mark Savers
Tricky questions and how to handle them
Wrong Idea vs Right Idea
Wrong idea
Right idea
Strong means hard to bend.
Strong means it can hold a load without breaking. Bending without breaking is flexibility.
Waterproof means water cannot touch it.
Waterproof means it does not let water pass through (and does not soak it up). Water sits on top as drops.
Big, heavy objects always sink.
A big wooden log floats, but a tiny metal pin sinks. Test it; do not guess by size.
Windows are glass because glass is strong.
Windows are glass mainly because glass lets most light through.
All plastic lets light through.
Some plastics let most light through, some let some through and some let none through.
To test fairly, change many things at once.
Change only one thing (the material). Keep everything else the same.
Exam Tip
Always give the property and link it to the use: "Plastic is waterproof, so rain does not soak through the raincoat and the person stays dry."
→ Magnets (Chapter 2): some metals, like iron and steel, are attracted to magnets.
→ Heat (Chapter 5): metal pots heat food quickly, while their handles are often plastic or wood.
Pip's trap alert"Strong" and "flexible" are not the same. Read the question carefully!
10SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
Mark Savers
SCIENCE MADE CLEAR
1
Materials
Model Answers
Use the C-S-E Chain: Cause → Science → Effect
Q1 · The raincoat
Explain why a raincoat is made of plastic and not cotton.
CauseRain falls on the raincoat.SciencePlastic is waterproof: it does not let water pass through. Cotton absorbs water.EffectThe rain does not soak through the plastic, so the person stays dry.
✕ Loses marks: "Plastic is better than cotton." This does not name the property.
Q2 · The best shelf
Siti hung masses on strips of the same size. Strip A broke at 3 masses, B at 7 and C at 5. Which material should she use for a bookshelf? Explain.
CauseStrip B held the most masses before breaking.ScienceMaterial B is the strongest: it can hold the heaviest load without breaking.EffectA shelf of B can hold heavy books without breaking. Choose B.
✕ Loses marks: "B is the hardest" or "B is the heaviest". The test measured strength.
Q3 · The spectacles
Explain why spectacle lenses are made of clear glass or clear plastic and not ceramic.
CauseLight must pass through the lenses into the eyes for the person to see.ScienceClear glass and clear plastic let most light through. Ceramic lets no light through.EffectThe person can see clearly through the lenses.
✕ Loses marks: "Glass is shiny" or "ceramic is ugly". Name the property about light.
Exam Keywordsstrongflexiblewaterproofdoes not let water pass throughfloats / sinkslets most light throughfair testproperty → use
Your Turn
Explain why a bathroom floor is covered with ceramic tiles and not carpet (fabric).
CauseScienceEffect
11SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
Model Answers
SCIENCE MADE CLEAR
1
Materials
Check Yourself
Six quick questions, then rate yourself
1Which property makes rubber a good material for a rubber band?
(2) A rubber band must bend and stretch without breaking.
2Ali tests which fabric is most waterproof. Name one thing he must keep the same.
Show answer
The number of drops of water, or the size of each fabric sample.
3Which lets the most light through: wood, clear glass, ceramic or metal?
Show answer
Clear glass.
4Give one property of wood that makes it suitable for a raft.
Show answer
Most wood floats (it is also strong).
5A metal spoon and a wooden spoon are placed in water. Predict what you will see.
Show answer
The metal spoon sinks. The wooden spoon floats.
6Explain why school bags are made of fabric and not glass.
Show answer
Fabric is flexible and strong, so the bag can fold and hold books. Glass is not flexible and breaks easily.
I can...
★★★name the seven materials and one use of each
★★★explain strength, flexibility, waterproof, floating and sinking, and light
★★★choose a material for a job and say why
★★★plan a fair test: change one thing, keep the rest the same
Colour one star for "a little", three for "I can teach it".
Try It at HomeThe float-or-sink hunt. Collect six small objects, such as a chopstick, a metal spoon and an eraser. Predict, then test each one in a basin of water.
Pip's Riddles
1. I am waterproof and let most light through. You drink from me. What am I made of?
2. I stretch, I bend, I grip the road. What material am I?
Pip saysMostly three stars? Great work! Next stop: Magnets.
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Check Yourself
SCIENCE MADE CLEAR
2
Magnets
Magnets
Core Idea: a magnet can pull or push, without even touching.
magnetpolesattractrepelmagnetic materialcompass
Core Idea
Magnets can be made of iron or steel. A magnet can act on some objects from a distance, without touching them. A magnet can do two things:
Attract
To pull something towards it.
A magnet attracts magnetic materials such as iron and steel, and the unlike pole of another magnet.
Repel
To push something away.
A magnet repels only the like pole of another magnet.
Unlike poles attract · Like poles repel
Why should I care? magnets keep doors shut, help sailors find their way, and help recycling plants pick out steel from rubbish.
Where You See It
At home A magnetic strip in the fridge door holds it shut. Fridge magnets hold up your spelling list.
Classroom Magnetic pencil cases snap shut, and posters stay up on the steel whiteboard.
HDB flat A magnetic door holder stops the main door from slamming on a windy day.
Recycling plant Strong magnets lift steel cans out of mixed rubbish so they can be recycled.
Pip Wonders...A compass has no battery and no brain. So how does it always know where North is? Find out on the Poles page!
At a Glance
MAGNETS
PolesN and S strongest at the ends
Attractiron, steel and unlike poles
Makestroke or electrical method
13SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
SCIENCE MADE CLEAR
2
Magnets
Meet the Magnet
How It Works: shapes, poles and pulling power
Magnets Come in Many Shapes
The shape does not decide how strong a magnet is. A small magnet can be stronger than a big one.
Every Magnet Has Two Poles
The magnetic force (pulling power) of a magnet is strongest at its poles, near the two ends. It is weakest in the middle.
Push or Pull?
A magnet can exert a pull (attract) or a push (repel). It does this without touching, and it can even work through paper, cloth or water.
Pull A magnet held near a steel paper clip pulls the clip towards it.
Push Two north poles held close together push each other apart.
Did You Know?
Some trains in other countries float above their tracks using powerful magnets. They are called maglev trains, and one in China has reached over 400 km/h!
What Are Magnets Made Of?
Magnets can be made of iron or steel. Steel is mostly iron. Many fridge magnets are made of other materials, but you only need to know iron and steel. Some kinds of stainless steel are not magnetic. Test it!
Pip saysWant to find the poles? Dip the magnet in paper clips. The poles are where most clips stick!
14SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
Meet the Magnet
SCIENCE MADE CLEAR
2
Magnets
Poles: Attract or Repel?
How It Works: unlike poles attract, like poles repel
Bring Two Magnets Together
N + S → attract
N + N or S + S → repel
The closer the poles are, the stronger the push or pull. Hold two like poles together and you can feel them pushing back against your fingers!
Did You Know?
The Earth acts like a giant magnet. That is why a magnet that can turn freely always lines up in a North-South direction.
A Hanging Magnet Points North
Hang a bar magnet on a thread so it can turn freely. It swings, then comes to rest with its N pole pointing North and its S pole pointing South.
Seen from above. The dot is where the thread holds the magnet.
The Compass
The needle of a compass is a tiny magnet that can turn freely. That is why it always points North and South. Pip's question is answered!
Pip's memory trickOpposites attract, just like a team of two friends who are different but stick together!
15SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
Poles: Attract or Repel?
SCIENCE MADE CLEAR
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Magnets
Magnet or Magnetic?
How It Works: three groups, one tricky test
Magnet
Magnetic material
Non-magnetic material
What is it?
Has poles and can attract or repel
Is attracted by a magnet, but has no poles of its own
Is not attracted by a magnet
Attracted by a magnet?
Yes (unlike pole)
Yes
No
Repelled by a magnet?
Yes (like pole)
Never
Never
Examples
bar magnet, compass needle
iron nail, steel paper clip, steel can
wood, plastic, rubber, glass, aluminium, copper
The Repel Test: Is It a Magnet?
Bring the N pole, then the S pole, of a magnet near each end of the mystery bar.
Repels at one end? It is a magnet. Only a magnet can be repelled.
Attracted at both ends, by both poles? It is a magnetic material, not a magnet. A magnet would repel at one end.
Careful: one attraction on its own proves nothing. Test both ends with both poles.
Magnets at Work
Compass: finds North on a hike at MacRitchie.
Whiteboard: magnets hold up notes.
Fridge door: a magnetic strip keeps it shut.
Pencil case: a hidden magnet snaps it shut.
Recycling: lifts steel cans, leaves aluminium.
Scrapyard crane: an electromagnet lifts scrap iron.
Spot the Impostor!
Pip has three bars that look the same. He tests each end with both poles of a magnet. Which bar is the real magnet?
Bar
End 1
End 2
?
A
attracted by N and S
attracted by N and S
…
B
repelled by N
attracted by N
…
C
no pull at all
no pull at all
…
Answer: B is the magnet (it was repelled). A is a magnetic material. C is non-magnetic.
16SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
Magnet or Magnetic?
SCIENCE MADE CLEAR
2
Magnets
Watch It
Is it a magnet? The repel test
1Pip has three bars, A, B and C, that look the same. Which one is a real magnet? Let us test them with a magnet.
2Exam trap! Bar A is pulled towards the magnet. Many pupils say "A is a magnet". Careful: a steel bar is pulled too, so one pull proves nothing.
3Test both ends of bar A with both poles. It is pulled every time and never pushed away, so A is a magnetic material, not a magnet.
4The N pole comes near bar B and B is pushed away. Only a magnet can be repelled, so B is a magnet. Like poles repel.
5Bar C does not move at all. It is a non-magnetic material, such as wood or plastic. Remember: when you test a bar with a magnet, only repulsion proves it is a magnet.
▶SCIENCE MADE CLEARWatch It · animated lesson
▶ Watch It: Is it a magnet? The repel test
SCIENCE MADE CLEAR
2
Magnets
Making Magnets
How It Works: the stroke method and the electrical method
1 · The Stroke Method
Place a steel bar (or steel needle) on the table.
Stroke it from one end to the other with one pole of a magnet.
At the end, lift the magnet away and bring it back to the start.
Repeat many times, always in the same direction with the same pole.
Check: the bar can now attract paper clips. More strokes usually make a stronger magnet.
Did You Know?
Long ago, sailors made compass needles by stroking an iron needle with a lodestone, a rock that is a natural magnet.
Careful Do not stroke back and forth. That makes the bar a weak magnet, or not a magnet at all.
2 · The Electrical Method
Coil insulated wire many times round an iron nail.
Connect the ends of the wire to batteries and a switch.
Close the switch so electric current flows. The nail becomes an electromagnet.
Remember: the iron nail is a magnet only while current flows. Switch off and it loses its magnetism, so the clips drop. (A steel bar in the coil can stay a magnet.)
Safety Do this only in class with your teacher. The wire can get hot.
Did You Know?
More turns of wire or more batteries make an electromagnet stronger. Scrapyard cranes use giant ones that can be switched on and off.
17SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
Making Magnets
SCIENCE MADE CLEAR
2
Magnets
Watch It
Make your own magnet: two methods
1This steel bar is not a magnet yet. The paper clips lie on the table and do not stick to it.
2Stroke method: stroke the bar with one pole of a magnet, from one end to the other, in one direction. Lift the magnet away, then repeat.
3Exam trap! Rubbing back and forth is not the stroke method. Always stroke in one direction and lift the magnet at the end of each stroke.
4After many strokes, the steel bar has become a magnet. Now it attracts the paper clips.
5Electrical method (only with your teacher): coil wire round an iron nail and connect it to a battery. Close the switch and the clips jump on.
6Open the switch and the clips fall off. This electromagnet works only while electricity flows through the wire.
▶SCIENCE MADE CLEARWatch It · animated lesson
▶ Watch It: Make your own magnet: two methods
SCIENCE MADE CLEAR
2
Magnets
Experiments You Must Know
Testing magnets and materials
1 · Magnetic or Not?
DoBring a magnet near objects made of different materials.SeeOnly objects of iron or steel are attracted.SoIron and steel are magnetic materials. Wood, rubber, plastic and aluminium foil are not.FairUse the same magnet at the same distance each time.
In real life Recycling plants use this to pull steel cans out of mixed rubbish.
2 · Where Is It Strongest?
DoTouch clips with the ends, then the middle, of a bar magnet. Count the clips held at each part.SeeThe ends hold the most clips. The middle holds very few.SoA magnet's magnetic force is strongest at the poles.
In real life A magnetic paper-clip holder grabs most clips near its edges, around the poles of the magnet inside.
3 · Is the Bar a Magnet?
DoBring each pole of a magnet near each end of the bar.SeeOne end of the bar is repelled by the N pole.SoThe bar is a magnet. Like poles repel, and only magnets can be repelled.NoteIf both ends of the bar are attracted by both poles, the bar is a magnetic material, not a magnet.
In real life You can check a compass needle this way: one end of it is pushed away by the N pole of a magnet.
18SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
Experiments You Must Know
SCIENCE MADE CLEAR
2
Magnets
Mark Savers
Tricky questions and how to handle them
Wrong Idea vs Right Idea
Wrong idea
Right idea
A magnet attracts all metals.
A magnet attracts only magnetic materials such as iron and steel. Aluminium and copper are not attracted.
The bar was attracted to the magnet, so it must be a magnet.
It may only be a magnetic material. When testing with a magnet, only repulsion proves it. (A bar that picks up paper clips on its own is a magnet.)
A magnet is strongest in the middle.
A magnet is strongest at its poles and weakest in the middle.
A bigger magnet is always stronger.
Size and shape do not decide strength. Test it by counting the clips each magnet attracts.
Stroke the steel bar back and forth.
Stroke in one direction only, with the same pole, lifting the magnet away at the end.
An electromagnet stays a magnet after it is switched off.
It is a magnet only while current flows through the coil.
Exam Tip
Name the material in your answer: write "the steel can is a magnetic material", not just "the can is metal".
Quick Summary
A magnet can pull (attract) or push (repel).
Magnets can be made of iron or steel.
Two poles, N and S. Strongest at the poles.
Unlike poles attract. Like poles repel.
A freely hanging magnet rests pointing North-South.
Magnets attract iron and steel (magnetic materials).
Make a magnet by the stroke or electrical method.
Link It Up
→ Materials (Chapter 1): being magnetic is another property we can use to sort materials.
→ Forces (Primary 5–6): a magnet's push or pull is called a magnetic force.
Pip's trap alertTesting with a magnet? "Attracted" is not proof. "Repelled" is!
19SCIENCE MADE CLEARUnderstand it. Explain it. Excel.
Mark Savers
SCIENCE MADE CLEAR
2
Magnets
Model Answers
Use the C-S-E Chain: Cause → Science → Effect
Q1 · Two mystery bars
Wei Jie brought bar X near bar Y and they attracted each other. He says both bars are magnets. Explain why he cannot be sure.
CauseThe two bars only attracted each other.ScienceA magnet attracts a magnetic material as well as the unlike pole of another magnet. Only magnets repel.EffectOne bar could be a magnetic material, so he must see them repel to be sure.
✕ Loses marks: "Because they are metal." This does not explain the attract and repel idea.
Q2 · Sorting cans
At a recycling plant, mixed cans pass under a strong magnet. Explain how this separates the steel cans from the aluminium cans.
CauseThe cans pass under a strong magnet.ScienceSteel is a magnetic material and is attracted. Aluminium is not a magnetic material.EffectThe steel cans are lifted away, and the aluminium cans stay behind.
✕ Loses marks: "The magnet attracts metal cans." Aluminium cans are metal too!
Q3 · The scrapyard crane
A crane lifts scrap iron with an electromagnet. When the operator switches it off, the scrap falls. Explain why.
CauseThe electric current was switched off.ScienceAn electromagnet is a magnet only while current flows through its coil.EffectIt loses its magnetism and no longer attracts the iron, so the scrap falls.
✕ Loses marks: "The magnet became weak." Say that it is no longer a magnet without current.
Your Turn
Siti hung a bar magnet from a thread. It turned for a while, then stopped with one end pointing North. Explain why.
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Model Answers
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Magnets
Check Yourself
Six quick questions, then rate yourself
1Which object will be attracted by a magnet?
(1) aluminium can(2) steel paper clip(3) copper wire(4) plastic ruler
Show answer
(2) Steel is a magnetic material.
2The N pole of one magnet is brought near the N pole of another. What happens?
Show answer
They repel (push apart). Like poles repel.
3A bar magnet is dipped into paper clips. Where do most clips stick?
Show answer
At the two ends (the poles), where the magnet is strongest.
4A bar magnet hangs freely from a thread. When it stops, which directions do its ends point?
Show answer
North and South (N pole to the North).
5Ravi strokes a steel needle many times with the S pole of a magnet, always in the same direction. Name this method.
Show answer
The stroke method.
6Mei's pencil case has a magnet in its flap and a steel plate in its body. Explain why the flap snaps shut.
Show answer
The magnet attracts the steel plate because steel is a magnetic material.
I can...
★★★say what magnets can do: attract and repel
★★★find the poles and say where a magnet is strongest
★★★predict if two poles attract or repel
★★★tell a magnet from a magnetic material
★★★make a magnet in two ways
Colour in one star for "a little", three for "I can teach it".
Try It at HomeThe floating compass. Ask an adult to help you. The adult strokes a sewing needle 30 times with one pole of a bar magnet, one way only, then tapes the needle flat on a plastic bottle cap. Float the cap in a bowl of water. Which way does the needle point?
Pip saysMostly three stars? Great work! Next stop: Matter.
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Check Yourself
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Matter
Matter
Core Idea: matter is anything that has mass and occupies (takes up) space.
massvolumesolidliquidgas
Core Idea
Everything around you is made of matter: your desk, the water in your bottle, and even the air you breathe. Matter has two things in common:
Mass
The amount of matter in an object.
Measured with a balance.
gkg
Volume
The amount of space an object takes up.
Measured with a measuring cylinder.
mllcm³
Has mass + takes up space = MATTER
Why should I care? once you know what matter is, you can explain why a balloon gets bigger, why a stone makes water rise and why a pump can push more air into a ball.
Where You See It
Recess Your water bottle holds water (liquid) and the empty part above it is full of air (gas).
PE lesson A flat basketball is pumped with air until it is hard and bouncy.
Hawker centre Ice kachang: solid ice, liquid syrup, all in one bowl.
Kitchen Oil poured into a pan spreads out to take the shape of the pan.
Pip Wonders...You cannot see air or hold it in your hand. So is air matter? Find the proof in Experiments You Must Know!
At a Glance
MATTER
Solidfixed shape fixed volume
Liquidno fixed shape fixed volume
Gasno fixed shape no fixed volume
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Matter
Is It Matter?
How It Works: ask two questions
The Two-Question Test
Does it have mass? Could it be weighed on a balance?
Does it take up space? Does it have volume?
Both YES → it is matter
If the answer to either question is no, it is not matter.
Did You Know?
The air inside your classroom has a mass of roughly 200 kg. That is about as heavy as three adults! You do not feel it because air is spread out all around you.
Clues That Air Is Matter
Blow into a balloon and it gets bigger: air takes up space.
A balloon full of air is heavier than an empty one: air has mass.
Invisible does not mean "not matter".Proof on the Experiments You Must Know page.
Sort It Out
✓ Matter
✕ Not Matter
Steam is matter (it is water as a gas). The heat that made it is not matter.
A shadow is only a dark area where light is blocked. It has no mass, so it is not matter.
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Is It Matter?
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Matter
Three States of Matter
How It Works: compare shape and volume
Solid
Liquid
Gas
Shape
Fixed shape
No fixed shape: takes the shape of the part of the container it fills
No fixed shape: takes the shape of the whole container
Volume
Fixed volume
Fixed volume
No fixed volume: spreads out to fill any container
Examples
stone, eraser, ice, coin
water, milk, cooking oil, syrup
air, steam, oxygen
Liquid: Same Volume, New Shape
The water changes shape to fit the bowl, but its volume stays at 100 ml. Nothing was added or taken away.
Gas: Fills the Whole Space
The scented gas spreads out until it fills every part of the box. A gas has no fixed shape and no fixed volume.
Pip's memory trickSolid = Stays the same. Liquid = Looks like its container. Gas = Goes everywhere.
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Three States of Matter
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Matter
Watch It
Solid, liquid or gas? Watch the shape and the volume
1A solid keeps its shape. Move the block from the bowl to the tray: it does not change shape or size.
2A liquid flows. Pour 100 ml of water into a wide dish: it takes the shape of the dish.
3Exam trap! The water level is lower, but there is not less water. A liquid has a fixed volume: still 100 ml.
4A gas spreads out. Spray air freshener into a closed jar: the gas fills every part of the jar.
5Remember: solid = fixed shape and volume; liquid = fixed volume only; gas = neither.
▶SCIENCE MADE CLEARWatch It · animated lesson
▶ Watch It: Solid, liquid or gas? Watch the shape and the volume
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Matter
Measuring Matter
How It Works: the right tool and the right unit
Mass
Electronic balance
Beam balance
Units:g grams, kg kilograms 1 kg = 1000 g
Volume of a Liquid
Use a measuring cylinder, or a beaker with markings for rough amounts.
Place it on a flat surface. Keep your eye level with the water. Read the mark at the bottom of the curved surface.
Units:mll1 l = 1000 ml 1 ml = 1 cm³
Did You Know?
A teaspoon holds about 5 ml. A can of drink holds about 320 ml. Singapore's reservoirs hold billions of litres of water!
Volume of a Stone: Displacement
A stone has an odd shape, so we cannot measure it with a ruler. Instead, we let it push water aside.
Volume of stone = 65 ml − 50 ml = 15 ml = 15 cm³
The water rises because the stone takes up space that the water used to fill.
Careful-scientist tip: the stone must be fully under water, and no water may splash out.
Read Pip's Cylinder
Pip drops a toy dinosaur into the water. What is its volume?Show answer47 ml − 40 ml = 7 cm³
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Measuring Matter
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Matter
Watch It
Measure a stone's volume like a careful scientist
1Stand the measuring cylinder on a flat table and pour in some water.
2Exam trap! Looking down from above gives the wrong reading.
3Bend down so your eye is level with the water. Read the bottom of the curved surface: 50 ml.
4Lower the stone gently on a thread until it is fully under water. The water rises to 65 ml.
5The stone took up space and pushed the water up. Volume of stone = 65 − 50 = 15 cm³.
▶SCIENCE MADE CLEARWatch It · animated lesson
▶ Watch It: Measure a stone's volume like a careful scientist
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Matter
Experiments You Must Know
Proving that air is matter
1 · Air Takes Up Space
DoPush a cup, upside down, straight into water.SeeThe tissue stays dry. Water enters only a little way.SoAir in the cup takes up space, so water cannot fill it.
Tilt the cup and bubbles escape. Water then rises and wets the tissue.
In real life Turn an empty bottle upside down in a basin. Water cannot rush in until air bubbles out.
2 · Air Has Mass
DoHang two equal balloons on a stick so it balances. Fill one with air.SeeThe side with the filled balloon tilts down.SoThe air added has mass.
In real life A diver's tank full of air is heavier than the same tank when it is empty.
3 · Gas Can Be Compressed
DoSeal the tip of a syringe of air and push. Repeat with water.SeeAir can be pushed into a smaller space. Water cannot.SoA gas has no fixed volume. A liquid has a fixed volume.
In real life A bicycle pump squeezes lots of air into a tyre to keep it firm.
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Experiments You Must Know
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Matter
Mark Savers
Tricky questions and how to handle them
Wrong Idea vs Right Idea
Wrong idea
Right idea
Air is "nothing", so an empty bottle has nothing in it.
An "empty" bottle is full of air. Air is matter: it has mass and takes up space.
A liquid has no fixed volume because it can flow.
A liquid has no fixed shape but a fixed volume. Flowing changes its shape only.
A gas keeps its volume and only changes shape.
A gas has no fixed shape and no fixed volume. It spreads out to fill its container.
A bigger object always has a bigger mass.
Size tells us volume. A big sponge can have a smaller mass than a small stone.
Light, heat and sound are matter because we can sense them.
We can sense them, but they have no mass and take up no space. They are not matter.
The water level rose because the stone added water.
The stone took up space and pushed the water up. The rise equals the stone's volume.
Exam Tip
When a question says "explain", name the property in full: write "air has mass" or "air takes up space", not just "because of air".
→ Heat (Chapter 5): when ice gains heat, it melts. The matter changes state, but it is still the same water.
→ Materials (Chapter 1): a material is matter that we use to make things.
Pip's trap alert"Empty" in a question usually means "full of air"!
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Mark Savers
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Matter
Model Answers
Use the C-S-E Chain: Cause → Science → Effect
Q1 · The dry tissue
Mei Ling pushed an upside-down cup with a tissue inside straight into a tank of water. Explain why the tissue stayed dry.
CauseThe cup was filled with air.ScienceAir takes up space, so the water could not fill the cup.EffectThe water did not reach the tissue, so it stayed dry.
✕ Loses marks: "Because of the air." This does not say what the air does.
Q2 · Pumping a ball
Raj pumped more air into a ball that was already full of air. The ball did not get much bigger. Explain how more air could fit inside.
CauseMore air was pushed into the ball.ScienceAir is a gas. A gas can be compressed (squeezed) into a smaller space.EffectMore air fitted inside the same ball, which made it harder.
✕ Loses marks: "The ball has space." Say the gas can be compressed.
Q3 · The rising water
A measuring cylinder had 40 ml of water. A marble was put in and the level rose to 52 ml. Find the marble's volume and explain the rise.
CauseThe marble was placed in the water.ScienceThe marble is matter and takes up space, pushing the water up.EffectThe level rose by 52 − 40 = 12 ml, so the marble's volume is 12 cm³.
✕ Loses marks: no unit, or "52 ml" (the final reading).
Your Turn
Jun Hao sealed the tips of two syringes. One held air and one held water. He could push in the plunger of the air syringe but not the water syringe. Explain why.
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Model Answers
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Matter
Check Yourself
Six quick questions, then rate yourself
1Which of these is not matter?
(1) steam(2) a shadow(3) cooking oil(4) air in a tyre
Show answer
(2) A shadow has no mass and does not take up space.
2Substance X takes the shape of its container and its volume stays the same in any container. What state is X?
Show answer
Liquid. No fixed shape, but a fixed volume.
3A gas fills a closed 200 ml container. All of it is moved into a closed 500 ml container. What is the volume of the gas now?
Show answer
500 ml. A gas spreads out to fill the whole container.
4Which apparatus would you use to find the mass of a key?
Show answer
An electronic balance (or a beam balance).
5A stone is put into 30 ml of water. The level rises to 38 ml. What is the stone's volume?
Show answer
8 cm³ (38 ml − 30 ml).
6Ahmad says an empty bottle has nothing inside. Explain why he is wrong.
Show answer
The bottle is filled with air. Air is matter because it has mass and takes up space.
I can...
★★★say what matter is, using mass and space
★★★sort things into matter and not matter
★★★compare solids, liquids and gases by shape and volume
★★★choose the right tool and unit to measure
★★★find a volume by displacement
Colour in one star for "a little", three for "I can teach it".
Try It at HomeThe balloon-in-a-bottle challenge. Push a balloon into an empty bottle, stretch its mouth over the bottle's neck, then try to blow it up. Why is it so hard? (Hint: what is already in the bottle?)
Pip saysMostly three stars? Great work! Next stop: Light and Shadows.
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Check Yourself
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Light
Light and Shadows
Core Idea: we see things when light from them enters our eyes.
light sourcereflectstraight linesshadowscreen
Core Idea
You can only see something when light from it enters your eyes. That light can come from the object itself, or bounce off it.
Light source
Gives out its own light.
e.g. the Sun, a light bulb, a fire, a torch
Reflects light
Does not give out light. Light bounces off it.
e.g. the Moon, a mirror, this book
Light travels in straight lines. Block it, and you get a shadow.
Why should I care? light explains why you cannot see in a dark room, why the Moon shines at night and why your shadow is long in the evening.
Where You See It
National Day Fireworks over Marina Bay give out their own light. They are light sources.
Void deck At night, the lights let you see the letterboxes. Light bounces off them into your eyes.
Puppet show Puppets held close to the lamp make giant shadows on the screen.
School field Your shadow is short at midday and long late in the afternoon.
Pip Wonders...The Moon glows brightly at night. Does the Moon make its own light? Turn the page to find out!
At a Glance
LIGHT
Sourcesgive out light
Seeinglight enters our eyes
Shadowslight is blocked
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Light
How Do We See?
How It Works: light sources and reflected light
Source or Not?
✓ Light sources
✕ Not light sources
A mirror, a safety vest and the Moon can look bright, but they only reflect light from a source.
Did You Know?
Light from the Sun takes about 8 minutes to reach Earth. Light is the fastest thing there is!
Pip's Quick Sort:light source or not?
lightninga silver ringa lit matcha road signa fireflya torch that is switched off
Answer: light sources = lightning, a lit match, a firefly. The others do not give out their own light.
How We See a Book
The lamp gives out light.
Light reflects off the book.
The reflected light enters your eyes, so you see the book.
In a completely dark room there is no light to reflect, so you cannot see the book at all.
Pip saysThe Moon is not a light source. It shines because it reflects light from the Sun.
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How Do We See?
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Light
Watch It
How do we see a book?
1In a completely dark room, you cannot see the book at all. There is no light.
2Switch on the lamp. The lamp is a light source: it gives out its own light.
3Light travels in a straight line to the book, reflects off it and enters your eye. Now you see the book.
4Trap! Light does not come out of our eyes. Light always travels from the object into the eye.
5The Moon works the same way. It is not a light source: it reflects light from the Sun into our eyes.
▶SCIENCE MADE CLEARWatch It · animated lesson
▶ Watch It: How do we see a book?
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Light
How Shadows Form
How It Works: light travels in straight lines
Light Travels in Straight Lines
Beams of sunlight through a window, or a torch beam in a dark room, have straight edges. Light does not bend around corners by itself.
Shiny Surfaces Reflect Well
Smooth, shiny surfaces such as a mirror, a steel spoon or still water reflect light very well. Dull, dark surfaces reflect less light.
HDB car park Round mirrors at corners let drivers see cars coming. Road safety Strips on vests reflect car lights so drivers can see you at night.
Making a Shadow
The ball blocks the light. Light travels in straight lines and cannot bend around it, so no light reaches the area behind the ball.
The shadow is on the opposite side of the ball from the light. Its outline matches the shape of the side facing the light.
Dark or Light Shadow?
Cardboardblocks all light: dark shadow
Tracing paperlets some light through: lighter shadow
Clear plasticlets most light through: very faint shadow
The more light a material blocks, the darker its shadow.
Pip saysA shadow is just a place that light cannot reach. It shows the outline only, never the colours.
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How Shadows Form
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Light
Changing a Shadow
How It Works: what makes a shadow bigger, smaller or move?
Torch Closer = Bigger Shadow
The closer the light is to the object, the more light the object blocks, so the shadow is bigger.
Shadow Changers
If you...
the shadow...
move the light closer to the object
gets bigger
move the object closer to the screen
gets smaller
use a bigger object
gets bigger
turn the object around
may change shape
move the light to one side
moves to the other side
Shadows from the Sun
The Sun seems to move across the sky from east to west.
Morning and evening: the Sun is low, so shadows are long.
Around midday: the Sun is high, so shadows are short.
The shadow always points away from the Sun.
Did You Know?
In Singapore the Sun is highest at about 1 pm, not 12 noon. Singapore is close to the equator, so in March and September the Sun is then almost overhead and your shadow can hide under your feet!
Pip's memory trick"Near the light, the shadow grows big. Near the screen, it shrinks."
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Changing a Shadow
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Light
More Shadow Secrets
How It Works: the screen, two objects and your hands
Object Closer to the Screen = Smaller Shadow
Keep the torch and screen still. As the object moves closer to the screen, it blocks less of the spreading light, so the shadow gets smaller and its edges look sharper.
Two Objects, How Many Shadows?
Side by sideTwo separate shadows.
One in front of the otherThe shadows overlap into one.
The position of each object decides where its shadow falls on the screen.
Shadow Puppets
Dog
Bird
Rabbit
Try it tonight with a torch. Switch off the room lights, shine a torch at a plain wall and make these shapes with your hands between the torch and the wall.
Move your hands closer to the torch: the shadow grows into a giant!
Move your hands closer to the wall: the shadow shrinks and gets sharper.
Turn your hands: the shadow changes shape.
Did You Know?
Shadow puppet theatre is hundreds of years old. Wayang kulit, from the Malay world, uses flat leather puppets held between a lamp and a cloth screen.
Pip saysEvery shadow puppet show uses the same rule: light travels in straight lines, and the puppet blocks it.
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More Shadow Secrets
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Light
Watch It
Shadow lab: what changes a shadow?
1The card blocks the light from the torch. Light travels in straight lines, so a shadow forms on the screen behind the card.
2Move the torch closer to the card. The card blocks more of the light, so the shadow gets bigger.
3Move the card closer to the screen. The card blocks less of the spreading light, so the shadow gets smaller.
4Trap! A red card does not make a red shadow. A shadow is just a dark area that light cannot reach.
5Add a second object at a different position. Each object blocks part of the light, so there are two shadows.
▶SCIENCE MADE CLEARWatch It · animated lesson
▶ Watch It: Shadow lab: what changes a shadow?
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Light
Experiments You Must Know
Testing how light and shadows behave
1 · Straight-Line Test
DoLine up three cards so their holes are in a straight line. Shine a torch through.SeeLight is seen through the holes. Move one card and the light cannot be seen.SoLight travels in straight lines. The moved card blocks it.
In real life You cannot see around a corner of a building, but you can hear someone there.
2 · Distance and Shadow Size
Changedistance from torch to objectKeep sameobject, screen position, torchMeasureheight of the shadow
Torch to object (cm)
Shadow height (cm)
10
30
20
15
30
10
SeeThe shorter the distance, the taller the shadow.SoWhen the torch is closer, the object blocks more of its light, so the shadow is bigger.
In real life Puppeteers bring a puppet near the lamp to make a giant shadow appear.
3 · Which Lets Light Through?
DoHold sheets of cardboard, tracing paper and clear plastic, one at a time, between a torch and a screen.Keep samesize of sheet, torch, distances
Material
Shadow
cardboard
dark
tracing paper
lighter (pale)
clear plastic
very faint
SoThe more light a material blocks, the darker the shadow it forms.
In real life Frosted glass in a bathroom lets some light in but stops people from seeing clearly through it.
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Experiments You Must Know
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Light
Mark Savers
Tricky questions and how to handle them
Wrong Idea vs Right Idea
Wrong idea
Right idea
The Moon is a light source.
The Moon reflects light from the Sun. It gives out no light of its own.
We see because light comes out of our eyes.
We see when light from an object enters our eyes.
A mirror gives out light.
A mirror only reflects light. In a dark room it looks dark too.
Moving the torch closer makes the shadow smaller.
The closer the light is to the object, the bigger the shadow.
A shadow shows the colour of the object.
A shadow is a dark area where light is blocked. It shows only the outline.
Clear glass forms a dark shadow, like wood.
Clear glass lets most light through, so its shadow is very faint.
The shadow is on the same side as the light.
The shadow is on the opposite side of the object from the light.
Exam Tip
For "how can she see it?", trace the path of light in order: light source → object → reflects → enters the eyes. Missing any step can cost a mark.
Quick Summary
A light source gives out its own light.
We see an object when its light enters our eyes.
Shiny, smooth surfaces reflect light well.
Light travels in straight lines.
A shadow forms when light is blocked.
Light closer to object: bigger shadow.
Link It Up
→ Materials (Chapter 1): how much light a material lets through decides how dark its shadow is.
→ Heat (Chapter 5): the Sun gives us both light and heat.
Pip's trap alert"Bright" does not mean "light source". Ask: does it make its own light?
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Mark Savers
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Light
Model Answers
Use the C-S-E Chain: Cause → Science → Effect
Q1 · Seeing in the dark
Ali could not see his book in a completely dark room. When he switched on the lamp, he could see it. Explain why.
CauseThe lamp was switched on and gave out light.ScienceLight from the lamp reflected off the book and entered Ali's eyes.EffectAli could see the book.
✕ Loses marks: "The room became bright." This does not say that light entered his eyes.
Q2 · The giant shadow
Siti moved a torch closer to her puppet. The screen stayed in the same place. The shadow became bigger. Explain why.
CauseThe torch was moved closer to the puppet.ScienceLight travels in straight lines. The puppet now blocked more of the light from the torch.EffectA larger area of the screen received no light, so the shadow was bigger.
✕ Loses marks: "The puppet got bigger." The puppet did not change; the amount of light blocked did.
Q3 · The lighter shadow
Ben shone a torch at a piece of cardboard and then at tracing paper of the same size. The tracing paper made a lighter shadow. Explain why.
CauseThe tracing paper was placed in front of the torch.ScienceTracing paper lets some light pass through, so it blocks only part of the light.EffectSome light reached the screen, so the shadow was lighter.
✕ Loses marks: "Tracing paper is thin." Say what it does to light.
Exam Keywordslight sourcereflectsenters the eyestravels in straight linesblocks lightlets some light throughopposite sidedistance
Your Turn
A cat walked between a lamp and a wall. A dark shape of the cat appeared on the wall. Explain why.
CauseScienceEffect
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Model Answers
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Light
Check Yourself
Six quick questions, then rate yourself
1Which of these is a light source?
(1) the Moon(2) a mirror(3) a candle flame(4) a white wall
Show answer
(3) A candle flame gives out its own light. The others only reflect light.
2Why can we see the Moon at night?
Show answer
Light from the Sun reflects off the Moon and enters our eyes.
3A torch is moved further away from a toy. The screen stays where it is. What happens to the shadow?
Show answer
It becomes smaller.
4Which forms the darkest shadow: clear glass, tracing paper or a wooden block?
Show answer
The wooden block. It blocks all the light.
5A lamp is on the left of a vase. On which side of the vase is its shadow?
Show answer
On the right, the opposite side from the lamp.
6Three cards had holes in a straight line. When Jun moved the middle card, he could no longer see the torch light. Explain why.
Show answer
Light travels in straight lines. The moved card blocked the light, so it could not reach his eyes.
I can...
★★★tell a light source from an object that reflects light
★★★explain how we see, using the path of light
★★★show that light travels in straight lines
★★★explain how a shadow forms
★★★predict how a shadow changes
Colour in one star for "a little", three for "I can teach it".
Try It at HomeThe shadow clock. Stand a bottle in a sunny spot. Trace its shadow with chalk at 9 am, 1 pm and 4 pm. Which shadow is the longest? Which way does each one point? Never look straight at the Sun.
Pip saysMostly three stars? Bright work! Next stop: Heat.
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Check Yourself
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Heat
Heat
Core Idea: heat is energy that flows from a hotter place to a colder place.
Heat is a form of energy. When something gains heat (from its surroundings), it becomes hotter. When it loses heat (to its surroundings), it becomes cooler.
Heat
A form of energy.
It flows from hotter to colder.
Temperature
How hot or cold something is.
Measured in °C
Common sources of heat:
the Sun
fire
electric heater
gas stove
Why should I care? heat explains why kopi cools down, why ice melts and why cooking pots have plastic handles.
Where You See It
Hawker centre Hot kopi left on the table slowly cools down as it loses heat to the surroundings.
After school Ice kachang melts because it gains heat from the warm air.
Void deck A metal railing in the afternoon Sun feels much hotter than a wooden bench.
Overhead bridge Bridges have small gaps at the joints so the metal can expand on hot days.
Pip Wonders...You drop ice into your Milo and it gets cold. Did the cold move into the drink? Find out on the next page!
At a Glance
HEAT
Gain heattemperature rises expands melts or boils
Lose heattemperature falls contracts freezes or condenses
Good conductorsmetals
Poor conductorswood, plastic, air, rubber
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Heat
Heat and Temperature
How It Works: heat flows from hotter to colder
Not the Same Thing
Heat
Temperature
What is it?
A form of energy
A measurement of how hot or cold something is
Unit
Unit: not needed for P4
degrees Celsius °C
Measured with
cannot be read on a thermometer
thermometer or datalogger with a temperature sensor
Pip's Contest: which has more heat?
Hot kopi 80 °C
VS
Warm swimming pool 30 °C
The pool! The kopi has the higher temperature, but the pool holds far more water, so it has much more heat.
Pip answersCold does not move! Your Milo loses heat to the ice. That is why the drink cools down and the ice melts.
Heat Flows: Hot → Cold
Heat flows out of the hot water into the cold water. The hot water's temperature falls. The cold water's temperature rises. This stops when both reach the same temperature.
Gain heat: temperature rises. Lose heat: temperature falls.
Using a Thermometer
Hold it by the top, not the bulb. Put the bulb fully into the liquid.
Wait until the reading stops changing. Read it with your eye level with the top of the liquid.
A datalogger with a temperature sensor records the temperature for you over time.
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Heat and Temperature
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Heat
Watch It
Where does the heat go?
1The kopi is hotter than the air around it, so heat flows out of the kopi into the air.
2The kopi loses heat, so its temperature falls until it is the same as the air. Then heat stops flowing.
3The canned drink is colder than the air, so heat flows from the air into the can.
4Exam trap! Many pupils write "cold flows out of the can". There is no such thing as cold flowing. Only heat flows.
5The can gains heat from the warmer air, so its temperature rises until it reaches 30 °C.
▶SCIENCE MADE CLEARWatch It · animated lesson
▶ Watch It: Where does the heat go?
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Heat
Expand and Contract
Effects of Heat: things change size
Most things expand (get bigger) when they gain heat, and contract (get smaller) when they lose heat.
Solids
Bridges and long railway tracks have small gaps. On hot days, the metal expands into the gap instead of bending.
Electric wires sag more on hot days.
A tight metal lid on a glass jar becomes easier to open under hot water: the metal lid expands more than the glass jar.
Liquids
The liquid in a thermometer gains heat, expands and rises up the tube.
When it loses heat, it contracts and the level drops.
Bottles of drinks are not filled to the very top, so there is room for the liquid to expand.
Gases
Put a dented ping-pong ball in hot water. The air inside gains heat, expands and pushes the dent out.
A balloon left in a hot car becomes bigger.
A balloon put in the fridge becomes smaller: the air inside loses heat and contracts.
Did You Know?
The Eiffel Tower in Paris is made of iron. On a hot summer day it can be up to about 15 cm taller than on a cold winter day!
Pip's reminderWhen something expands, its mass stays the same. It only takes up more space.
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Expand and Contract
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Heat
Watch It
Expand and contract around us
1On a hot day the metal of the bridge gains heat and expands. The small gap gives it room, so the bridge does not bend.
2Warm water on a tight jar: the metal lid gains heat and expands more than the glass jar, so the lid becomes loose.
3In the fridge the air in the balloon loses heat and contracts. In the Sun it gains heat and expands.
4Exam trap! Expanding does not add matter. The object gets bigger, but its mass stays the same.
▶SCIENCE MADE CLEARWatch It · animated lesson
▶ Watch It: Expand and contract around us
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Heat
Change of State
Effects of Heat: solid, liquid and gas
Water Can Change State
Melting: ice kachang gains heat from the warm air and melts.
Freezing: water in an ice tray loses heat in the freezer and turns into ice.
Boiling: water in a kettle gains heat and boils, turning into steam.
Condensing: steam touches a cold metal lid, loses heat and turns back into water droplets. Cold can: water vapour in the surrounding air loses heat to the cold can and condenses on its outside.
Watch Ice Melt
The ice gains heat from the warm air and the Sun, which are warmer than it is. It melts into water. The water is the same matter, only in a different state.
Did You Know?
Steam (hot water vapour) from a kettle is an invisible gas. The white "smoke" you see is made of tiny water droplets, formed when the steam loses heat to the cooler air.
Pip's tipMelting and boiling need heat to be gained. Freezing and condensing happen when heat is lost.
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Change of State
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Heat
Conductors of Heat
How It Works: some materials let heat flow quickly
Good or Poor?
Good conductors
Let heat flow through them quickly.
Metals
for example steel, copper, aluminium
Poor conductors
Let heat flow through them slowly.
Wood · Plastic Air · Rubber
A poor conductor does not stop heat completely. It only slows down the flow of heat.
Did You Know?
In an air-conditioned room, a metal chair feels colder than a wooden one, yet both are at the same temperature. Metal takes heat from your skin faster.
Race of the Rods
Wax beads melt off the metal rod first, starting nearest the hot water. The beads on the plastic rod stay on much longer.
Using Conductors Wisely
Cooking potMade of metal, a good conductor, so heat flows quickly to the food.
Pot handleMade of plastic or wood, poor conductors, so heat flows slowly to your hand.
Wooden ladleStays cool enough to hold while you stir hot soup, because wood is a poor conductor.
Oven glovesThick cloth traps air, a poor conductor, so heat from the hot tray reaches your hand slowly.
Cooler boxPlastic and foam slow down heat flowing in from the warm air, so the ice melts slowly.
Thermos flaskAn empty space (vacuum) between two walls slows heat flow. Hot drinks stay hot and cold drinks stay cold.
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Conductors of Heat
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Heat
Experiments You Must Know
Testing how heat behaves
1 · Hot Water Cools Down
DoLeave a beaker of hot water in the classroom. Record its temperature with a datalogger.SeeThe temperature falls quickly at first, then stops at room temperature.SoThe water loses heat to the cooler air until both are at the same temperature.
In real life Forget your kopi at the hawker centre and it ends up at the same temperature as the air.
2 · Ball and Ring
DoA metal ball just fits through a ring. Heat the ball, then try again.SeeThe hot ball cannot pass. After cooling, it passes again.SoA solid expands when it gains heat and contracts when it loses heat.
In real life This is why bridges and long rail tracks need small gaps at their joints.
3 · Which Cup Keeps Ice Longest?
Changethe material of the cup only.Keep samestarting size of the ice cube, size, shape and thickness of the cup, place.SeeIce in the metal cup melts first. Ice in the foam cup lasts longest.SoFoam is a poor conductor, so heat from the air flows in slowly.
In real life Picnic cooler boxes at East Coast Park use foam and plastic to keep drinks cold.
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Experiments You Must Know
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Heat
Mark Savers
Tricky questions and how to handle them
Wrong Idea vs Right Idea
Wrong idea
Right idea
The ice gives "cold" to the drink.
The drink loses heat to the ice. Only heat flows, from hotter to colder.
Heat and temperature mean the same thing.
Temperature tells how hot or cold. Heat is energy. A pail of water at 60 °C has more heat than a cup at 60 °C.
A metal spoon feels cold because metal is colder than wood.
Both are at the same temperature. Metal, a good conductor, takes heat from your hand faster.
A poor conductor stops heat from flowing.
A poor conductor slows down the flow of heat.
The white cloud above a boiling kettle is steam.
Steam is invisible. The cloud is tiny water droplets formed as steam loses heat.
Drops on a cold can leaked out.
Water vapour in the air loses heat to the can and condenses.
A ball that expands becomes heavier.
Its mass stays the same. Only its volume increases.
Exam Tip
Always say where heat flows from and to. Write "The hot kopi loses heat to the cooler surroundings", not "the kopi becomes cold".
Quick Summary
Heat is a form of energy.
Temperature is how hot or cold something is, in °C.
Heat flows from hotter to colder until both reach the same temperature.
Gain heat: temperature rises, things expand, ice melts, water boils.
Lose heat: temperature falls, things contract, water freezes, steam condenses.
Metals are good conductors. Wood, plastic, air and rubber are poor conductors.
Link It Up
→ Matter (Chapter 3): expanding means the volume increases while the mass stays the same.
→ Materials (Chapter 1): we choose metal or plastic depending on whether heat should flow quickly or slowly.
Pip's trap alertIf you write the word "cold" as something that moves, cross it out!
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Mark Savers
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Heat
Model Answers
Use the C-S-E Chain: Cause → Science → Effect
Q1 · The stuck lid
Siti could not open a tight metal lid on a glass jar. She ran hot water over the lid and it opened easily. Explain why.
CauseHot water was run over the metal lid.ScienceThe metal lid gained heat from the hot water and expanded more than the glass jar.EffectThe lid became looser on the jar, so it was easier to open.
✕ Loses marks: "The heat made the lid soft." Metal does not soften in hot tap water. Say it expanded.
Q2 · The pot handle
A cooking pot is made of steel, but its handle is made of plastic. Explain why the handle is made of plastic.
CauseThe steel pot becomes very hot on the stove.SciencePlastic is a poor conductor of heat, so heat flows slowly from the pot to the handle.EffectThe handle does not get too hot, so we can hold it without burning our hands.
✕ Loses marks: "Plastic does not let heat through." It slows heat, it does not stop it.
Q3 · Drops on the tray
Ali held a cold metal tray above a kettle of boiling water. Water droplets formed under the tray. Explain how the droplets formed.
CauseSteam from the kettle touched the cold tray.ScienceThe steam lost heat to the colder tray and condensed.EffectThe steam changed into water droplets under the tray.
✕ Loses marks: "The tray made the steam cold." Say the steam lost heat to the tray.
Your Turn
Mrs Tan's kopi was at 85 °C. After 20 minutes on the table, it was at 30 °C, the same as the room. Explain why the temperature fell and then stopped falling.
(3) Wood is a poor conductor. The others are metals.
2A cup of water at 70 °C stands in a tray of water at 25 °C. In which direction does heat flow?
Show answer
From the cup to the tray water, until both reach the same temperature.
3The liquid in a thermometer rises. Is the liquid gaining or losing heat?
Show answer
Gaining heat. It expands and rises.
4Why do bridges have small gaps at their joints?
Show answer
So the metal can expand on hot days without bending.
5Name the change of state when ice cream gains heat.
Show answer
Melting (solid to liquid).
6A dented ping-pong ball became round in hot water. Explain why.
Show answer
The air inside gained heat and expanded, pushing the dent out.
I can...
★★★tell the difference between heat and temperature
★★★explain how heat flows from hotter to colder
★★★give examples of expansion and contraction
★★★name the changes of state
★★★pick good and poor conductors for a job
Colour in one star for "a little", three for "I can teach it".
Try It at HomeSpoon race. Ask an adult to pour warm water from the tap (not from the kettle) into a mug. Stand a metal spoon and a wooden chopstick in it. After one minute, touch the tops. Which is warmer, and why?
Did You Know?
Singapore's record high is 37.0 °C (Tengah 1983, Ang Mo Kio 2023).
Pip saysYou finished the book! You are a Physical Science explorer.
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Check Yourself
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Answers
Check Yourself answers for every chapter
Chapter 1 · Materials
1. (2) 2. Number of drops or size of sample 3. Clear glass 4. Floats (strong) 5. Metal sinks, wood floats 6. Fabric is flexible and strong; glass breaks easily. Riddles: 1. glass 2. rubber Your Turn: Water splashes on the floor (Cause). Ceramic tiles are waterproof and do not absorb water, but carpet absorbs water (Science). The floor does not get soaked and is easy to dry and clean (Effect).
Chapter 2 · Magnets
1. (2) 2. They repel 3. At the poles (ends) 4. North and South 5. Stroke method 6. The magnet attracts the steel plate, because steel is a magnetic material. Your Turn: The magnet could turn freely (Cause). A freely hanging magnet comes to rest pointing North-South (Science). So its N pole pointed North (Effect).
Chapter 3 · Matter
1. (2) 2. Liquid 3. 500 ml 4. Electronic balance 5. 8 cm³ 6. The bottle is full of air, which has mass and takes up space. Read Pip's Cylinder: 7 cm³. Your Turn: Cause: the plungers were pushed. Science: air is a gas with no fixed volume, so it can be compressed into a smaller space; water is a liquid with a fixed volume, so it cannot be compressed. Effect: the air plunger moved in but the water plunger did not.
Chapter 4 · Light
1. (3) 2. Sunlight reflects off the Moon into our eyes 3. Smaller 4. Wooden block 5. Right side 6. Light travels in straight lines, so the moved card blocked the light and it could not reach his eyes. Your Turn: Cause: the cat was between the lamp and the wall. Science: the cat blocked the light, and light travels in straight lines so it cannot bend around the cat. Effect: no light reached that part of the wall, so a shadow formed.
Chapter 5 · Heat
1. (3) 2. From the cup to the tray water 3. Gaining 4. So the metal can expand 5. Melting 6. The air inside gained heat and expanded, pushing the dent out. Your Turn: The hot kopi lost heat to the cooler surroundings. Heat flows from hotter to colder until both are at the same temperature, so the kopi cooled to 30 °C and then stopped cooling.
Pip saysGot one wrong? Go back to that page, find the idea, then try again. That is how scientists learn!
48SCIENCE MADE CLEARUnderstand it. Explain it. Excel.