PSLE Magnets & Heat — Physical Science Cheatsheet

TEACH Lesson Summary — Teach This First

Suggested flow: walk through these 8 points with your student first (this is the lesson), then let them attempt the question bank, and finish by going back over the topic cards below as a conclusion. Each point below is a generalisation of what the questions in this document actually test.

1Matter has mass and takes up space — and materials are chosen by their properties. A beam of light is NOT matter; water, clouds and melting ice cream are. When a question asks which material to use (netting, bottle, shell), match EVERY required property in the table: strength supports a load, flexibility bends and returns, waterproof stops water, translucent lets some light through so you can read it. Reshaping an object changes its shape but never its mass.

2Magnets: repulsion is the only proof that something really is a magnet. A magnet attracts unmagnetised magnetic materials too, so attraction alone is ambiguous. Repulsion happens ONLY between two magnets with like poles facing — if you see it, both objects are confirmed magnets. Opposite poles attract, like poles repel; and a moving magnet can have friction, gravity AND magnetic force acting on it at once.

3Heat flows from hot to cold through conductors — metals are good, air is poor. A metal wire carries heat from a flame (that is why the paper lantern burned along the wire). To keep something HOT you wrap it in an insulator: a double-walled bottle with AIR between keeps coffee hot because air conducts poorly and the coffee loses less heat. Poor conductors still get scorched over time if they sit above a fire long enough.

4Solids expand when heated and contract when cooled — use that to solve fitting problems. To fit a too-small metal rim onto a wheel, HEAT THE RIM so it expands and slips on; it contracts as it cools and grips. Telephone wires sag in the heat and snap at night as they cool and shrink — leave slack so contraction has room. A cold jar lid grips tight (metal contracts more than glass); warming both loosens it.

5Changes of state happen at fixed temperatures, shown by a FLAT part on the graph. Melting (solid→liquid), freezing (liquid→solid), boiling (liquid→gas) and condensation (gas→liquid). On a temperature–time graph, the flat section means the substance is changing state — heat is being gained or lost but the temperature stays put. Boiling at 100 °C means GAINING heat, never losing it.

6Evaporation happens below the boiling point and speeds up with more surface area and air flow. Rank cups by how much open water they show — widest dries first. If a sample's mass falls while it warms, some liquid has evaporated into steam and escaped (not boiled). More exposed surface or added heat also makes ice cream melt faster.

7Light makes shadows; energy changes form but is never created from nothing. A shadow grows when the object moves CLOSER to the light or the screen moves FURTHER away. Energy conversions are chains: solar panel turns LIGHT into electrical; a ringing phone goes stored chemical → electrical → sound; a wound rubber band gives elastic potential → kinetic of propeller and boat. To cut household energy use, target the LARGEST pie-chart slice first.

8Forces change shape, speed or direction — never mass; and rolling beats sliding on friction. A force can bend a paper plane, speed it up or turn it, but cannot change its mass. A ball rolls further than the same plasticine as a cube because ROLLING has less friction than sliding (not more energy). In circuits, batteries must connect positive-to-negative for current to flow, and an electromagnet only attracts iron while the circuit is closed.

The mark-earning habit for this whole paper: give cause → effect, not just a label. Name the process (conduction, expansion, evaporation, repulsion) AND explain what happens to the object. One complete sentence with both parts usually earns full marks where a bare keyword does not.

1 Materials & Properties of Matter

Choosing a material from its properties (netting Q4 · medicine bottle Q31)

Read the property table row by row and match EVERY required property — one ✗ in a needed column disqualifies that material
Netting to keep people out: must be strong + flexible + allow light through → pick the row with all three ✓
Medicine bottle you can read the level of: must be waterproof AND allow some light to pass (translucent) — opaque fails even if it floats or is waterproof

What matter is and isn't (Q11, Q30)

Matter has mass and takes up space. A beam of light is NOT matter; a cloud, water and melting ice cream all are
Twisting the balloon: its SHAPE changes but the MASS OF AIR stays unchanged — reshaping does not add or remove air (Q30)

Property words to keep straight (Q1 crab shell · jar lid, 2nd set Q14)

STRENGTH = supports a load / protects without breaking (crab shell W); FLEXIBILITY = bends and returns; WATERPROOF = water cannot pass through
A plastic bottle can be squeezed because the material is FLEXIBLE — it changes shape under force, then springs back

2 Magnets & Magnetic Forces

Attraction vs repulsion — the only reliable test (Q35 steel bars)

ATTRACT can happen between a magnet and an unmagnetised magnetic material OR between opposite poles — so attraction alone does NOT prove something is a magnet
REPULSION happens ONLY between two magnets with like poles facing → if you see repulsion, BOTH objects are definitely magnets
Q35 logic: X and Y attract (one may be unmagnetised); Z attracts one bar but shows NO repulsion to either → only the bar that can repel is confirmed a magnet. Work each row's yes/no before choosing.

Forces acting on a moving magnet (Q3 slope)

A magnet sliding down a slope and stopping has THREE forces at rest: friction, gravitational force AND magnetic force — tick all three in the table
Pattern for 'which forces acted' tables: list every force present at that moment; do not drop one just because it is invisible (magnetic force still acts)

Finding poles from a turning magnet (Q18)

A hanging magnet R turns when two magnets approach — the pole facing each approaching magnet tells you P and Q: like poles repel, opposite attract
Match the direction of rotation to which side is being pushed vs pulled, then read off the N/S at P and Q from the options table

3 Heat Conduction — Good & Poor Conductors

Good conductors (Q6 candle lantern, Q22 coffee bottle)

METAL is a good conductor of heat: in the paper lantern the metal wire carried heat from the flame to part X, so it burned first
To keep coffee HOT you want an INSULATOR — bottle Q with AIR between two walls, because air is a poor conductor and the coffee loses LESS heat to the surroundings (Q22)

Poor conductors / insulators (Q36 leaves on fire)

Leaves are POOR conductors of heat — yet they still get burnt marks over time because heat slowly passes through them while they sit above the fire
Answer format: name the material's conductivity AND what that does to the object ('the leaves are poor conductors, but heat still passed through and scorched them')

Reading a cooling graph (pan of oil, 2nd set Q3)

Temperature falls over time as the hot pan cools; ROOM TEMPERATURE = the flat final value the temperature settles at
'When did she add the vegetables?' = the point where the cooling curve CHANGES SLOPE — a new event interrupts the steady fall

4 Thermal Expansion & Contraction

Fitting a rim onto a wheel (Q5)

To fit a too-small metal RIM over a metal WHEEL: HEAT THE RIM — it expands and its inner diameter grows, so it slips on; as it cools it contracts and grips tightly

The classic trap: you heat the part that must GET BIGGER (the rim), not the wheel. Cooling would make everything smaller and tighter.

Wires snapping at night (Q8 telephone lines)

Material S EXPANDS when heated by the sun in the day, then CONTRACTS as it cools at night — wires pulled tight in the heat shrink and snap under tension
'How to build so they won't snap?' → leave SLACK/sag in the wires (or use a shorter length) so contraction has room without breaking them

Glass top cracking + jar lid (2nd set Q6 · 2nd set Q14)

Part A of the glass top is hotter than part B because it sits directly over the hot pot — heat conducts up through contact; uneven heating makes the glass expand UNEVENLY and crack
A cold jar from the fridge: the metal/plastic lid contracts more than the glass when cold, gripping tight. Left at room temperature both WARM AND EXPAND, loosening the grip so the lid comes off easily (Q14b)

5 Changes of State — Melting, Freezing, Boiling, Condensation

Definitions to state in one line (Q6a boiling, Q9a freezing)

BOILING: a liquid changes to gas at its boiling point; FREEZING: a liquid changes to solid at its freezing point; MELTING: solid → liquid; CONDENSATION: gas → liquid
At 100 °C water changing from liquid to gas is BOILING and it is GAINING heat (Q41) — evaporation/boiling always needs heat in, not out

Reading a temperature–time graph (Q24 freezing curve)

The FLAT part of the line = a change of state happening at constant temperature. On AB the water is CHANGING FROM LIQUID TO SOLID (freezing) — it is not simply 'getting cooler' there
A flat section means heat is being lost/gained but the temperature does NOT move until the whole sample has changed state

Freezing & boiling points table (Q9)

At 30 °C: a substance with freezing point BELOW 30 and boiling point ABOVE 30 is a LIQUID; below its freezing point = solid; above its boiling point = gas
Substance stored as 150 cm³ in a 100 cm³ container at 30 °C must be the one that is SOLID there (a liquid/gas would not hold a fixed volume) — match each substance's state at 30 °C to decide P, Q or R
Can you store Q in an open tray at 30 °C? Only if Q is a solid then; if it is a liquid it will spread/flow out of the gaps (Q9c)

Solid forming in a pipe (Q3c oil sink)

Oil F has a melting point of 40 °C. Poured hot into the sink it is liquid, but as it cools BELOW 40 °C it FREEZES to a solid and blocks the water pipe at X — even though no solid waste entered

6 Evaporation & Drying

Order cups dry fastest → slowest (Q34)

Evaporation is faster with a LARGER exposed surface area and more air flow. Rank the four cups by how much open surface their water has — widest opening dries first, narrowest last
Answer format: give the order AND the reason ('cup P dries fastest because it has the largest surface area for evaporation')

Mass falling while heating ice (Q37)

After 4 minutes the mass of water is LOWER than the starting ice — some of the melted WATER HAS EVAPORATED into steam and escaped, so the sample lost mass

The classic trap: it is not 'all the ice melted' or 'some boiled to steam' (no boiling at these temperatures) — evaporation happens below the boiling point too

Ice cream melting faster (Q16)

John's melts faster because he SUPPLIES HEAT (holding it) AND his temperature rose — more heat in = faster melting. A larger exposed surface area also speeds melting; pick every statement that adds heat or exposure

7 Light, Shadow & Energy Conversions

Making a shadow bigger (Q21 puppet)

A shadow gets BIGGER when the object is CLOSER to the light source OR the screen is FURTHER from the object — move the puppet nearer the light / screen further away
Move the audience: no effect on shadow size. Only the light–object–screen geometry matters.

Shadow length over time (Q14 lamp post)

A FLAT (constant) shadow-length line means Eva was STANDING STILL near the lamp post — her distance from the light did not change
Walking towards → shorter shadow; walking away → longer shadow. A steady value = no movement.

Energy conversion chains (Q15 solar, Q23 phone, Q2b boat)

Solar panel: LIGHT energy → electrical energy (powers the lamp at night). Phone ringing: potential (stored chemical) → electrical → sound
Rubber-band boat: elastic potential in the wound band → kinetic of the propeller + kinetic of the boat (+ heat/sound lost). Fill each box with an ENERGY TYPE, not a force

Cutting household energy use (Q40 pie chart)

The biggest slice = the biggest saving. The air-conditioner is 40% → using a FAN instead of the A/C cuts the largest share; switching off lamps (8%) saves far less
Always target the LARGEST percentage first when asked how to reduce usage most.

8 Forces & Friction

Effects of forces — what a force CANNOT do (Q38 paper plane)

A force can change an object's SHAPE, SPEED or DIRECTION. It CANNOT change its MASS — 'change in mass' is the not-possible option

Direction of forces on an object (Q39 tissue holder)

The spring pushes the tissue paper AWAY from the wall (force X direction) while gravity pulls it DOWN — match both arrows to the correct row
Read each force's direction independently, then find the single option where BOTH are right.

Friction: rolling beats sliding (Q33 cube vs ball)

The same plasticine as a BALL rolls past L while the CUBE only slides to K — a rolling object has LESS frictional force than a sliding one, so it travels further

The classic trap: the ball does NOT have more potential energy at J (same mass, same height) and gravity is unchanged — the difference is FRICTION (rolling < sliding)

Straight-line motion & joints (Q25 toy train)

The train did not go straight because the JOINTS let each carriage turn independently — the force on the carriages was not all in one direction
Friction at the wheels slows it but does not bend its path; the turning joints are why it wanders.

Fair test with a spring balance (Q13 surface area)

To test 'force needed is NOT affected by surface area', compare two runs where ONLY surface area differs and mass stays the same → A vs B (20 g, 4 cm² vs 8 cm²) or C vs D
Pick the pair that changes ONE variable (surface area) while holding the other (mass) constant — that is the fair test.

9 Springs & Elastic Force (Hooke's Law)

Force vs compression graph shape (Q12, Q27)

The line goes through the ORIGIN with a POSITIVE slope: more force → more compression. Any graph that does not start at zero or slopes down is wrong
A steeper line = a STIFFER spring (needs more force for the same compression). Compare two springs by which line rises faster.

Reading values off the spring/wire graphs (Q8a, Q27)

'Length at 0 °C' = read straight across from temperature 0 on the axis. 'Increase from 0 to 60 °C' = subtract the two readings — do the arithmetic, don't eyeball it
For pellets pushed into a holder: each extra pellet adds force and compresses the spring further in equal steps → evenly spaced points on a straight line through the origin.

10 Electrical Circuits & Electromagnets

Why a bulb won't light (Q17 battery orientation)

A series circuit needs the batteries connected POSITIVE-to-NEGATIVE so current flows. If a bulb stays dark with a working cell, one battery is likely REVERSED — turning it around completes the loop
Work each change in the options table: which single fix (connect X/Y to T, or flip a battery) actually closes the circuit.

Counting bulbs that light up (Q26 five bulbs)

Trace the current path from one terminal of the cell back to the other; every bulb ON that closed loop lights. Count how many MORE than are already lit when the switch closes
A bulb in a broken branch or shorted out will not light — follow the wire, not the number of bulbs drawn.

Electromagnet: iron bar moving between A and B (Q4)

When S is closed the coil becomes an electromagnet that ATTRACTS the iron bar up to one contact; the circuit breaks, the magnetism stops, the bar falls back — it repeats, so bulb P flickers on/off
'Which bulb(s) light when the bar is at A?' = whichever bulb's loop is CLOSED by the bar touching contact A. Read the diagram's contacts before answering.
Brightness of Q at B: if more current flows through Q in that position it gets BRIGHTER; explain with current, not just 'it lights'.

🧠 Chapter Concept Map