Series route: This guide belongs to the complete PSLE Learner’s Guide volume directory. The original PSLE Learning Guide supplies the wider English, Mathematics and Science route, while PSLE Science provide verified subject-specific continuation.
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This volume solves one precise learner problem: the learner says friction simply “creates heat” without tracing the energy source, or assumes every rubbing test warms equally regardless of force, speed, duration, material and measurement. The aim is not to memorise a slogan. It is to understand the mechanism well enough to recognise the idea when the wording, numbers, diagram or context changes. A Primary 6 learner should be able to explain the decision, perform it under time pressure, and detect a tempting answer that only looks familiar.
- Understand the mechanism before memorising a form.
- Study the worked examples and compare near-misses.
- Repair common misconceptions with targeted tests.
- Complete graded independent practice before reading the answers.
- Use delayed transfer and examination control to make the skill durable.
- Use the parent and tutor notes only after the learner has attempted the work.
The problem beneath the mistake
Rub your palms together for several seconds and they may feel warmer. The warming is linked to work done while the surfaces move against friction.
The energy does not appear from nowhere. Chemical energy in the body supports muscle action, movement occurs, and energy is transferred into thermal energy in the hands and surroundings.
Friction is the contact force that opposes relative motion or the tendency for surfaces to slide. It acts while the rubbing motion continues.
A temperature rise is an observable effect, but it is not identical to the amount of energy transferred. Mass, material, surface area and energy lost to surroundings affect the reading.
Pressing harder can increase the contact interaction and the work needed over the same rubbing distance, but a fair test must control other variables before concluding.
Rubbing faster changes both speed and often total distance covered in a fixed time. A good investigation defines exactly what is being compared.
Longer rubbing usually allows more work to be done, yet heat also transfers away to air and nearby objects. The temperature may not rise at a constant rate.
Different materials respond differently. Roughness, deformation, conductivity, mass and surface condition can all affect friction and measured temperature.
Friction is not always unwanted. It lets shoes grip floors, brakes slow wheels, pencils mark paper and hands hold objects. Warming is one possible energy-transfer effect.
Lubricants can reduce friction by changing the contact between surfaces. A comparison must use equal amounts and recognise safety and cleanup constraints.
Touch is not a precise thermometer. Skin senses energy transfer rate as well as temperature, so use an appropriate sensor when quantitative evidence is required.
The reliable routine is name the energy source, identify the rubbing surfaces, describe motion against friction, state the thermal-energy transfer, predict a possible temperature rise, and control the test variables.
Core decision: When a force moves contacting surfaces against friction, work is done. Part of the energy associated with the motion is transferred to thermal energy of the surfaces and surroundings, so their temperature may rise.
A useful rule has three parts: a trigger, an operation and a check. The trigger tells you when the rule applies. The operation tells you what to do. The check tells you whether the result still matches the meaning of the question. Learners who remember only the operation often apply it in the wrong place; learners who remember only an example often freeze when the surface details change.
Mechanism: why the rule works
1. Name the source
The moving system needs an energy supply.
Diagnostic question: What provides the motion? Reliable response: Trace chemical, electrical or stored energy into movement.
2. Identify contact
Friction acts between specified surfaces.
Diagnostic question: Which two surfaces slide relative to each other? Reliable response: Name both instead of saying friction acts alone.
3. Track work
A force acts through a distance while rubbing continues.
Diagnostic question: What motion occurs against resistance? Reliable response: Connect force and travel qualitatively.
4. State the transfer
Some motion-related energy becomes thermal energy.
Diagnostic question: Which objects warm? Reliable response: Include both surfaces and possible surroundings.
5. Measure outcome
Temperature is measured rather than guessed from touch.
Diagnostic question: What sensor, point and time are used? Reliable response: Take consistent before-and-after readings.
6. Control variables
Force, duration, distance, speed, material, mass and starting temperature matter.
Diagnostic question: What one factor is changed? Reliable response: Hold the others reasonably constant.
Worked examples: make the decision visible
Do not race through these examples. Before reading each explanation, name the evidence that matters and the information that does not. Then compare the correct route with the tempting route. That comparison is where the transferable learning sits.
Worked example 1: Palms
Task. A learner rubs palms together for ten seconds.
Reasoning. Muscles do work against friction at the contact surfaces. The controlling idea is the work done against friction and how that transferred energy is distributed and measured. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. The palms may warm.
Independent check. Energy ultimately comes from the body’s chemical energy stores. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 2: Brakes
Task. Brake pads press a moving wheel or disc.
Reasoning. Friction reduces motion while thermal energy increases in the brake components and surroundings. The controlling idea is the work done against friction and how that transferred energy is distributed and measured. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. The brakes can become hot.
Independent check. Do not touch recently used brakes. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 3: Eraser
Task. An eraser is rubbed repeatedly on paper.
Reasoning. Work is done against friction and materials deform. The controlling idea is the work done against friction and how that transferred energy is distributed and measured. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. The eraser and paper may warm slightly.
Independent check. Crumbs also show wear. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 4: Lubrication
Task. Matched surfaces slide with and without a suitable lubricant.
Reasoning. Lubrication changes the contact interaction and can reduce work against friction. The controlling idea is the work done against friction and how that transferred energy is distributed and measured. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. The lubricated setup may show less warming under matched conditions.
Independent check. Only conclude from controlled measurements. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 5: Duration test
Task. The same blocks are rubbed for 5, 10 and 15 seconds at controlled motion.
Reasoning. More rubbing time can mean more work and transfer. The controlling idea is the work done against friction and how that transferred energy is distributed and measured. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Longer trials may give larger temperature rises.
Independent check. Cooling during the trial prevents assuming perfect proportionality. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 6: Harder pressing
Task. The same surfaces are rubbed over the same path while normal force differs.
Reasoning. Greater pressing can increase frictional resistance. The controlling idea is the work done against friction and how that transferred energy is distributed and measured. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. More work and warming may occur.
Independent check. Speed and distance must stay controlled. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 7: No sliding
Task. Two surfaces press together but do not move.
Reasoning. Static friction may act, but there is no rubbing distance in this setup. The controlling idea is the work done against friction and how that transferred energy is distributed and measured. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. The same frictional warming mechanism is not demonstrated.
Independent check. Separate pressure from sliding. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Worked example 8: Sensor comparison
Task. A thermometer records 25.0°C before and 27.2°C after.
Reasoning. The sensor provides quantitative temperature evidence. The controlling idea is the work done against friction and how that transferred energy is distributed and measured. This prevents a learner from choosing an answer merely because one word, number or observation resembles a remembered example.
Answer. Temperature increased by 2.2°C.
Independent check. State resolution and placement. A good check approaches the conclusion from a different direction. Repeating the same steps more slowly may repeat the same hidden assumption.
Deepening lab: compare cases, conditions and limits
A method becomes independent when you can say where it applies, where it stops and which change would alter the conclusion. The cases below deliberately vary one structural feature at a time. For each case, pause before the analysis and predict whether the core rule remains available. Then name the exact condition that controls the decision. This is harder than repeating a worked solution, but it is also closer to what an unfamiliar examination item demands.
Deepening case 1: Slow rub
Case. Surfaces move slowly for a fixed number of strokes.
Analysis. Time for heat loss differs from fast rubbing. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Choose a fair comparison basis. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 2: Fast rub
Case. More strokes may occur in the same time.
Analysis. Both speed and distance can change. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Count strokes or total path. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 3: Rough surface
Case. A rough texture may produce different friction and deformation.
Analysis. Rougher does not universally mean a simple fixed value. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Measure rather than assume. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 4: Smooth surface
Case. A smooth pair can still have friction.
Analysis. Microscopic contact and material properties matter. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Avoid saying no friction. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 5: Large mass
Case. The same energy spread through more mass can cause a smaller temperature rise.
Analysis. Temperature response depends on mass and material. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Control specimen size. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 6: Small sample
Case. A small object may warm measurably with modest energy.
Analysis. It can also cool quickly. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Standardise delay before reading. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 7: Metal surfaces
Case. Metal conducts thermal energy away from the contact rapidly.
Analysis. A sensor location can affect results. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Measure at a defined point. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 8: Wood surfaces
Case. Wood transfers thermal energy differently from metal.
Analysis. Material comparison involves more than friction. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Do not attribute every difference to roughness. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 9: Air drag
Case. Moving objects also experience resistance from air.
Analysis. The dominant mechanism depends on setup. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Name the contact medium. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 10: Tyres
Case. Tyres warm through deformation and friction during use.
Analysis. Multiple processes contribute. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Avoid a one-cause overclaim. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 11: Match lighting
Case. Some matches ignite because rubbing raises local temperature and triggers chemical reaction.
Analysis. This is hazardous and not a classroom rubbing test. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Do not reproduce it. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 12: Drill bit
Case. Drilling can heat tool and material.
Analysis. Work against friction and cutting deformation transfer energy. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Use protective procedures. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 13: Machine bearing
Case. Poor lubrication can increase friction and warming.
Analysis. Monitoring temperature can signal a problem. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Keep the explanation qualitative. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 14: Hands feel warm
Case. Touch reports sensation, not a calibrated temperature.
Analysis. Blood flow and moisture also affect feeling. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Use a thermometer. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 15: Cooling pause
Case. A delay before measurement allows energy to leave.
Analysis. Late readings underestimate the immediate peak. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Fix the timing. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 16: Starting temperature
Case. Warm and cool samples cannot be compared fairly without accounting for initial conditions.
Analysis. Use change in temperature and matched starts. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Record baseline. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 17: Same number of strokes
Case. Equal stroke count may still have unequal force, length and speed.
Analysis. A fair test needs operational definitions. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Use guides or masses where safe. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 18: Energy conservation
Case. Mechanical energy decreases while thermal energy and other forms increase.
Analysis. Total energy is transferred, not destroyed. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Name sound and deformation as possible outputs. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 19: Temperature plateau
Case. Warming may slow as transfer to surroundings increases.
Analysis. Input and losses can approach balance. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Do not expect indefinite rise. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Deepening case 20: Safety boundary
Case. Excessive rubbing can damage skin or materials.
Analysis. Useful evidence does not require injury or high temperature. Notice that the answer depends on the work done against friction and how that transferred energy is distributed and measured; changing a decorative detail would not be enough to change the reasoning.
Challenge. Use short, gentle, supervised trials. State the conclusion in one precise sentence, then add one sentence that names the evidence or relationship that makes it valid.
Finish the lab with a blank-page recall. Write the rule, its conditions, one confirming example, one near-miss and one independent check from memory. Compare that page with the article only after finishing. If the rule is correct but the condition is missing, the learning is not yet safe: an overgeneralised rule can produce confident errors. If the condition is correct but no example can be generated, practise construction rather than rereading.
Common misconceptions and targeted repairs
Misconception 1: Friction makes energy from nothing
What the learner may think. Heat is created without a source.
Why it fails. Work is supplied by muscles, motors or moving objects. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Trace the energy pathway. Use this short test immediately: What drives the motion?
Misconception 2: Heat and temperature are identical
What the learner may think. A higher temperature means exactly the same energy transfer in every object.
Why it fails. Mass and material affect temperature change. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Separate measured temperature from transferred energy. Use this short test immediately: Are samples matched?
Misconception 3: Rougher always warms more
What the learner may think. Texture alone fixes the result.
Why it fails. Material, force, wear and motion also matter. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Test matched samples. Use this short test immediately: What variables changed?
Misconception 4: Pressing without moving is rubbing
What the learner may think. Contact pressure alone demonstrates frictional warming.
Why it fails. The described work requires movement through distance. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Observe relative motion. Use this short test immediately: Did sliding occur?
Misconception 5: Touch is precise
What the learner may think. Hands can measure exact temperature.
Why it fails. Sensation depends on transfer rate and physiology. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. Use a sensor. Use this short test immediately: What reading was recorded?
Misconception 6: All motion becomes heat in one surface
What the learner may think. Only one object receives the energy.
Why it fails. Both surfaces, air, sound and deformation can share it. The error feels efficient because it removes a decision, but it also removes the evidence boundary that makes the answer valid.
Targeted repair. State the system boundary. Use this short test immediately: Where else can energy go?
Graded independent practice
Attempt each item without looking ahead. Write one line that identifies the controlling evidence before writing the final answer. Items 1–3 check recognition, 4–7 require explanation, and the later items change the surface form so that memory alone is insufficient.
Practice 1: Recognition
Question. Why can rubbing hands make them warmer?
Explained answer. Muscles do work moving the hands against friction, transferring energy to thermal energy in the hands and surroundings.
Why this answer earns trust. The explanation includes source, contact, work and effect. Transfer variation: Apply to brakes.
Practice 2: Variables
Question. Name five factors to control in a rubbing test.
Explained answer. Materials, force, duration, distance or strokes, speed, mass, starting temperature, sensor position and reading time are valid.
Why this answer earns trust. Controls isolate the chosen factor. Transfer variation: Choose one independent variable.
Practice 3: Measurement
Question. Why is touch insufficient?
Explained answer. Skin sensation is not calibrated and depends on energy-transfer rate and body conditions.
Why this answer earns trust. A thermometer gives quantitative evidence. Transfer variation: Specify resolution.
Practice 4: Energy source
Question. What is the original source when a learner rubs blocks by hand?
Explained answer. Chemical energy in the body enables muscle action and movement.
Why this answer earns trust. Energy does not appear from nowhere. Transfer variation: Trace through motion to thermal energy.
Practice 5: No movement
Question. Two blocks are pressed but not slid. What is missing?
Explained answer. Rubbing distance and work through sliding are missing.
Why this answer earns trust. Pressure alone is not the tested mechanism. Transfer variation: Add controlled motion.
Practice 6: Comparison
Question. One sample rises 2°C and another 4°C. Can friction alone be declared greater?
Explained answer. Not unless mass, material, starting conditions and measurement are controlled.
Why this answer earns trust. Temperature change has multiple determinants. Transfer variation: List missing controls.
Practice 7: Cooling
Question. Why may temperature rise slow during a long trial?
Explained answer. Thermal energy is also transferred to surroundings, so losses grow as the object warms.
Why this answer earns trust. Input is not perfectly stored. Transfer variation: Predict after rubbing stops.
Practice 8: Lubricant
Question. What does lubricant change?
Explained answer. It changes contact and can reduce frictional resistance and warming under matched conditions.
Why this answer earns trust. The exact result needs measurement. Transfer variation: Design a safe test.
Practice 9: Safety
Question. Why avoid high-speed or prolonged rubbing?
Explained answer. It can burn skin, damage materials or create unsafe temperatures.
Why this answer earns trust. Short gentle trials are sufficient. Transfer variation: Set a stop rule.
Practice 10: Independent chain
Question. State the complete mechanism.
Explained answer. Energy source drives motion; contacting surfaces move against friction; work transfers energy into thermal energy; temperature may rise while some energy spreads to surroundings.
Why this answer earns trust. The chain is conservative and testable. Transfer variation: Apply to bicycle brakes.
Delayed transfer: prove that the learning lasts
Transfer test 1: Energy maps
Draw source-to-motion-to-thermal pathways for hands, brakes and erasers. Do this after a delay, without rereading the worked examples. The purpose is to test retrieval and decision-making, not immediate imitation.
Success criterion. Every map names the energy supply and receiving objects. If the criterion is not met, return to the smallest missing decision rather than repeating the entire chapter.
Transfer test 2: Fair-test design
Plan matched rubbing trials with one changed factor. Do this after a delay, without rereading the worked examples. The purpose is to test retrieval and decision-making, not immediate imitation.
Success criterion. Variables, sensor placement and timing are explicit. If the criterion is not met, return to the smallest missing decision rather than repeating the entire chapter.
Transfer test 3: Delayed explanation
After two days, explain frictional warming without saying energy is created. Do this after a delay, without rereading the worked examples. The purpose is to test retrieval and decision-making, not immediate imitation.
Success criterion. The response traces work and transfer. If the criterion is not met, return to the smallest missing decision rather than repeating the entire chapter.
Examination control
1. Read the job before the story. Underline the command and the noun it governs. “Explain the change,” “state the word,” “find the fraction” and “identify the evidence” are different jobs even when the surrounding context is similar.
2. Separate given information from remembered information. Use only the facts supplied for the current task plus secure subject knowledge. Do not let a previous question, a familiar worksheet or an expected pattern silently become new evidence.
3. Write enough working to expose the decision. A marker or teacher should be able to see the relationship that justifies the answer. Extra sentences are not automatically stronger; the strongest working is concise, relevant and checkable.
4. Reserve a different-route check. For language, read the sentence for meaning and grammar. For mathematics, estimate or reverse the operation. For science, check the claim against the stated observation and a conservation or fair-test principle.
5. Stop when the requested job is complete. Unrequested speculation can contradict a correct answer. Add detail only when it explains the mechanism or satisfies another explicit part of the question.
Under time pressure, use a compact four-part margin routine: trigger → evidence → operation → check. Trigger names the feature that activates the method. Evidence identifies the exact words, values or observations allowed. Operation performs the language, mathematical or scientific step. Check asks whether the final statement answers the requested job, preserves units or referents, and avoids a stronger claim than the evidence supports.
A compact error log
After practice, do not record only “careless mistake.” Name the broken decision. Useful labels include trigger missed, evidence imported, relationship reversed, referent lost, unit dropped, operation correct but job wrong, and check repeated the same route. Add one prevention cue beside the label. A short accurate log is more useful than a long emotional account because it tells the learner what to do on the next item.
Review the log after two days and again after a week. Reattempt only one or two representative items first. If the method transfers, move to a mixed set. If it fails, repair the exact link between trigger and operation. This spacing matters because a solution can feel obvious while it is still visible and disappear when the page is closed.
Notes for parents and tutors
Use only gentle hand rubbing or safe room-temperature materials; do not create high temperatures.
Ask “where did the movement energy come from?” before accepting “friction made heat.”
Record actual before-and-after temperatures when possible, and discuss why touch and sensors can disagree.
The adult’s most useful question is not “Why were you careless?” but “Which decision did the evidence require?” Ask the learner to point to the controlling word, value, relationship or observation. If the learner can explain that link, reduce support. If the learner cannot, model one example and then change the surface details for the next attempt.
Frequently asked questions
Why does rubbing make surfaces warmer?
Work is done against friction and energy is transferred into thermal energy.
Does friction create energy?
No; the energy comes from the system driving the motion.
Does rougher always mean hotter?
No. Many variables affect friction and measured temperature.
Is temperature the same as heat?
No. Temperature is a state measurement; thermal energy transfer depends on the process and system.
Why do brakes get hot?
Friction and deformation transfer energy from motion into thermal energy.
What makes a fair test?
Change one factor while controlling materials, force, motion, duration, starting conditions and measurement.
Next routes
Return to the complete volume directory to locate the series, use the original PSLE Learning Guide for the foundation route, and continue through PSLE Science for verified subject guidance. The next useful task is a mixed set in which this idea is sometimes relevant and sometimes irrelevant; that is the point at which a learner must choose, not merely copy.