Energy, Heat & Thermal Design — Print · Science 6: Matter, Energy & Earth Systems, Grade 6
How do energy transfers explain cooling and a feasible thermal design? Which feasible sleeve slows cooling under the matched model, and what should be redesigned?
Printable chapter lessons and review.
Forms of Energy & Evidence of Transfer
Learning goals
- I can name the store an object's energy is in and say what it depends on.
- I can give the observable evidence that energy has been transferred.
- I can compare energies in joules across very different situations.
Readings for this unit
Before this unit
Read the chapter opening and the named observation or diagram. Clarify one word or unit that blocks understanding. Recall the relevant earlier measurement, matter, or energy idea.
Study the unit across three 35–45-minute class sessions. Use the worked examples after an attempt and the supplied records when actual equipment is not available.
Lift a 2 kg book from the floor to a shelf 1.5 m up and you have given it about 30 J of gravitational potential energy. Drop it and that 30 J becomes movement, and when the book hits the floor the 30 J becomes a small amount of sound and a slightly warmer patch of floor and book.
Nothing in that sequence was ever visible. What you actually saw was a book in a higher place, then a book moving fast, then a noise. Energy is the accounting we keep across those changes, and the reason it is worth keeping is that the total stays the same.
The unit is the joule, written J, and it is small. A single AA battery stores roughly 10,000 J. A slice of bread holds around 300,000 J of chemical energy. Climbing one flight of stairs costs a 60 kg person about 1800 J.
Build your understanding
Where this fits
This chapter is about energy, and it opens with the hardest idea in it: energy is not a substance you can point at. The next lesson follows energy through a chain of changes and shows that the total is conserved, the two after that deal with heat specifically, and the chapter ends with a design task where you use all of it to keep something warm.
Use three flexible 40-45-minute sessions: the stores energy sits in; the evidence that a transfer has happened; the four pathways and comparing quantities in joules, then the practice set, revision and the exit check. Workshop, review, quiz and exams have separate time.
Part 1 · Where energy sits
It helps to think of a small number of stores rather than a long list of forms. An object that is moving has kinetic energy, and it depends on both mass and speed, so a lorry crawling through a car park can carry more of it than a sprinting athlete. An object that has been raised has gravitational potential energy, which depends on mass and height: lifting 2 kg through 1.5 m stores about 30 J, and lifting the same book 3.0 m stores about 60 J, because doubling the height doubles the energy. A stretched spring or a drawn bow has elastic potential energy. A warm object has thermal energy, which is the energy of its particles jiggling about. And fuel, food and batteries hold chemical energy in the arrangement of their particles.
The stores are worth keeping straight because they explain different things. Chemical energy in food is why you can climb stairs at all; gravitational potential energy is why being at the top of the stairs is different from being at the bottom; thermal energy is why you are warmer after the climb than before it. A single flight of stairs for a 60 kg person is about 1800 J of gravitational store gained, while the body actually uses something like four or five times that much chemical energy to do it, and the difference goes to warming you up. That gap is the subject of the next lesson.
Pause and explain
A 2 kg book is lifted 1.5 m and gains about 30 J. How much would it gain if lifted 3.0 m, and why?
Check your reasoning after answering
About 60 J. Gravitational potential energy depends on mass and height together, so with the mass unchanged, doubling the height doubles the energy stored. The same reasoning works for mass: a 4 kg book raised 1.5 m would also gain about 60 J, because doubling either quantity doubles the result.
Part 2 · Evidence that something moved
Since energy cannot be seen, every statement about it has to be backed by an observable change, and there are only a few of these. Something starts moving or speeds up. Something gets warmer, which you can measure with a thermometer. Something emits light. Something makes a sound. Something that was squashed or stretched springs back. When you say energy has been transferred, you should be able to point at one of those and say that is how I know.
This discipline catches a common mistake. A student who says that a battery gives energy to a bulb has made a claim; the evidence is that the bulb emits light and becomes warm, and both can be checked. A student who says a stationary rock on a table has a lot of energy because it is heavy has not made a checkable claim at all, since nothing about the rock is changing. Energy stored does matter, but what makes the store real is that it can be released and the release can be observed, which is why the first chapter's insistence on separating observation from inference applies here too. There is one more piece of evidence that is easy to overlook: something runs out. A battery stops working, a candle burns down, a wound spring unwinds. A store being depleted is just as observable as a bulb lighting up, and in many investigations it is the easier of the two to measure, because you can weigh the fuel before and after.
Pause and explain
What observable evidence shows that energy has been transferred from a battery to a bulb?
Check your reasoning after answering
The bulb emits light and gets warmer, and both can be measured rather than assumed. The battery also runs down over time, which is a second check. Without one of these observable changes there is no evidence of a transfer, however reasonable the claim sounds.
Part 3 · Four ways it travels
Energy moves between stores along a small number of pathways, and naming the pathway is part of describing what happened. It can move mechanically, when a force pushes something through a distance, as when you lift the book. It can move electrically, when a current flows through a component, as in the bulb. It can move by heating, when a temperature difference drives energy from the hotter thing to the cooler one. And it can move by radiation, as light or infrared, which is how energy reaches Earth across 150 million km of empty space with nothing in between to carry it.
The pathway and the store are different questions and students often merge them. A kettle is a good test case: the pathway is electrical, the store the energy arrives in is thermal, and the evidence is the water temperature rising from about 20 degrees Celsius to 100 degrees Celsius. A campfire warming your hands uses a different pathway, radiation, to fill the same kind of store. Being able to say both parts, which pathway and into which store, is the whole skill this section is teaching. Radiation deserves a second look because it is the one that works through nothing at all. Conduction and convection both need matter to carry the energy along, but radiation crosses a vacuum, which is why the Sun can heat Earth across 150 million km of empty space and why a thermos flask has a silvered inner surface to reflect it back. Chapter 3's fourth lesson takes all three apart properly.
Pause and explain
A kettle heats water. Name the pathway and the store, and say why they are different questions.
Check your reasoning after answering
The pathway is electrical, since a current flowing through the heating element is what delivers the energy, while the store it ends up in is thermal, shown by the water rising from about 20 to 100 degrees Celsius. The pathway describes how energy travelled; the store describes where it now sits, and the same store can be filled by different pathways, such as radiation from a fire.
Part 4 · Getting a sense of the numbers
Joules only become useful once you have a few reference points, because 1 J on its own means nothing to anybody. Dropping an apple from waist height releases roughly 1 J. Climbing a flight of stairs costs about 1800 J. An AA battery holds around 10,000 J. A slice of bread carries about 300,000 J, and a day's food for an adult is somewhere near 10,000,000 J. Because food energy is often printed in Calories, it is worth knowing that one food Calorie is 4184 J, so a 250 Calorie snack bar is just over 1,000,000 J.
Lining those up tells you something that is hard to get any other way. A single AA battery holds about as much energy as five or six trips up a flight of stairs, and one slice of bread holds thirty times what the battery does. Food is a remarkably concentrated energy store, which is why a person can work all day on a few hundred grams of it, and why the batteries in portable devices are the limiting factor they are. Comparing quantities in the same unit is a habit worth building now, because it turns a list of facts into a set of relationships. One warning about the units you will meet outside school. Electricity bills are measured in kilowatt hours rather than joules, and 1 kWh is 3,600,000 J, so a household using 10 kWh in a day has used 36,000,000 J. Food packets in some countries give kilojoules and in others Calories. None of these are different kinds of energy; they are different sized boxes for counting the same thing.
Pause and explain
A slice of bread holds about 300,000 J and an AA battery about 10,000 J. What does the comparison tell you?
Check your reasoning after answering
That food is a far more concentrated energy store, holding about thirty times as much as the battery. It explains why a person can work for hours on a small amount of food while a portable device runs down quickly, and it is only visible because both quantities are expressed in the same unit and can therefore be divided.
Apply the whole unit · Follow the energy
A 60 kg student climbs a 4.0 m staircase, which stores about 2400 J of gravitational potential energy. At the top they are breathing hard and feel warm. A fitness tracker says the climb used about 10,000 J of food energy.
Your task
Account for the energy, naming stores and pathways, and explain the difference between the two figures.
What your response should show
- Names the chemical store and the mechanical pathway correctly
- Calculates the useful fraction as roughly 24 per cent of the total
- Identifies the thermal store as the destination of the remainder
- Gives observable evidence rather than asserting where the energy went
Response guidance — after your attempt
Name the store the energy started in and the pathway by which it reached the student's new position.
State how much of the 10,000 J ended up as gravitational potential energy, as a fraction.
Explain where the rest went and give the observable evidence for it.
The energy started in the chemical store of the student's food and moved mechanically, through muscles exerting force over a distance, into the gravitational potential store, which gained 2400 J. That is 2400 out of 10,000 J, or about 24 per cent, so roughly three quarters of the energy used did not end up lifting the student at all. The rest went mainly into the thermal store of the student's body and the surrounding air, and there is direct observable evidence for this: the student feels warm and is breathing hard, and their skin temperature and the air immediately around them would both measure slightly higher than before. A smaller amount went into sound, as footsteps. Nothing was destroyed along the way; the 10,000 J is all still accounted for, just spread between a useful store and a dispersed one.
Scientific references for this unit
- US Energy Information Administration: energy units and comparing quantities
- Institute of Physics: teaching energy stores and pathways
- US Department of Agriculture: food energy values and the food Calorie
- NASA: how energy from the Sun reaches Earth by radiation
Parent / teacher teaching notes
Begin with the literal observation, quantity, or diagram relationship. Ask the learner to explain why the evidence supports the claim, check a relevant unit or boundary, then discuss an alternative. The supplied numbers are illustrative, not real observations. A parent can read aloud and allow a spoken rehearsal before writing. Judge science and evidence rather than political, faith, or family agreement. Use the complete data option whenever an actual procedure is unavailable or unsuitable.
The key idea
You never observe energy directly, only what it does: something speeds up, warms up, lights up or makes a sound. Every claim about energy in this course is really a claim about one of those observable effects, measured in joules.
Worked examples
Example 1 · Identify energy and matter
- Identify source and receiving pathways.
- Account for the stated energy quantities.
- Distinguish joules from grams and temperature units.
Example 2 · Transfer to a different case
- Identify the distinction and conditions in this new case.
- Use the relevant mechanism or quantity; preserve units and the chosen boundary.
- Explain why the answer fits and what further evidence would be needed.
Example 3 · Describe position within an interacting system · a focused example
- State the literal condition or observation in the example.
- Apply the distinction explained in this teaching part.
- Check whether the claim stays within the given evidence.
Avoid these mistakes
- Misleading claim: Temperature in degrees Celsius is an amount of energy in joules.
- Misleading claim: An energy form can be identified without describing any process or system.
- Omitting units, measurement timing, or a model boundary makes the evidence hard to interpret.
- Treating illustrative classroom data as real field measurements or copying a model is not an independent explanation.
Check your understanding
Does increasing speed increase the car’s mass?
Discuss the answer
No. It changes the energy associated with motion, not the amount of matter in the car.
Why must a reference position be stated?
Discuss the answer
Potential energy comparisons depend on relative positions and the chosen reference; a height number alone is incomplete.
Is light the same substance as battery material?
Discuss the answer
No. Light transfers energy by radiation; battery matter and emitted radiation are different parts of the explanation.
Why is a list of forms not a complete explanation?
Discuss the answer
The explanation must connect the stages and observable changes, including transfers to surroundings rather than merely naming categories.
Sustained scientific explanation and revision
These activities are scheduled in the parent plan. Save a first response, a correction, and the reason for the change in the science notebook.
Activity 1 · Forms of Energy & Evidence of Transfer · Model and explain
Read Two Cups and One Question and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Forms of Energy & Evidence of Transfer, study Parts 3–4 and attempt the worked case: Explain the energy forms and why temperature or casing mass alone would not measure the 100 J. Explain the steps before opening the model.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
The modeled 100 J transfers into 25 J light and 75 J thermal pathways. Mass in grams describes matter, while a temperature reading in °C is not an energy total. The unchanged casing mass does not mean no energy transfer occurred, and this illustrative partition is not a measurement of every flashlight.
Activity 2 · Forms of Energy & Evidence of Transfer · Practice, revise and exit
Read Two Cups and One Question and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Forms of Energy & Evidence of Transfer, complete practice questions 1–6 and both choice checks, then answer independently: Two identical stationary books lie on shelves at different heights. Which energy comparison is relevant? Save a correction explaining one changed claim or method.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
Gravitational potential energy relative to a common reference. The higher book has greater potential energy in the book–Earth system under matched mass and gravity conditions.
Words to know
- kinetic energy
- Energy associated with motion.
- potential energy
- Energy associated with relative position or configuration in an interacting system.
- evidence
- A relevant observation, measurement, or record used to evaluate a claim.
- system boundary
- The chosen limit specifying what is included and which exchanges cross it.
- uncertainty
- A stated limit in measurement or knowledge, distinct from a careless mistake.
In the real world
Reading the forms of energy helps you understand your whole home: the chemical energy in food fuels your body, electrical energy runs your devices, and light and thermal energy pour out of every lamp and heater.
Exit check
Two identical stationary books lie on shelves at different heights. Which energy comparison is relevant?
Check your explanation after answering
Gravitational potential energy relative to a common reference. The higher book has greater potential energy in the book–Earth system under matched mass and gravity conditions.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.
Energy Transformations, Conservation & Dissipation
Learning goals
- I can calculate efficiency as useful output divided by total input.
- I can explain how energy can be conserved and wasted at the same time.
- I can explain why dissipated energy cannot easily be collected and reused.
Readings for this unit
Before this unit
Read the chapter opening and the named observation or diagram. Clarify one word or unit that blocks understanding. Recall the relevant earlier measurement, matter, or energy idea.
Study the unit across three 35–45-minute class sessions. Use the worked examples after an attempt and the supplied records when actual equipment is not available.
An old filament light bulb drawing 60 J every second turns about 3 J of that into light and about 57 J into heat. It is a 5 per cent efficient lamp and a 95 per cent efficient heater, which is a fair description of what it actually is. An LED doing the same lighting job converts around 40 per cent into light.
In both cases every joule is accounted for. Nothing vanished; the filament bulb simply sent most of its energy into warming the room instead of lighting it. Conservation of energy says the total before equals the total after, and it says nothing at all about how much of the total ends up where you wanted it.
The energy that goes where you did not want it is said to be dissipated. It is still there, spread through the air and the walls as a very slight temperature rise, and the problem is precisely that it is spread: there is no practical way to gather it back up.
Build your understanding
Where this fits
The last lesson named the stores and the pathways. This one follows energy through a change and introduces the two ideas that make the accounting useful: the total is conserved, and the useful fraction is almost always small. Efficiency figures from this lesson come back in the chapter's design task, where improving one is the whole point.
Use three flexible 40-45-minute sessions: conservation and the useful fraction; calculating efficiency from real figures; dissipation and why waste heat cannot be recovered, then the practice set, revision and the exit check. Workshop, review, quiz and exams have separate time.
Part 1 · Conserved and wasted at the same time
These two statements sound contradictory and are not. Energy cannot be created or destroyed, so the total in a closed system is fixed; that is conservation. Meanwhile most of the energy a machine takes in ends up somewhere useless; that is waste. The resolution is that waste describes where energy went, not whether it still exists. When a filament bulb turns 57 J out of every 60 J into heat, those 57 J are entirely present in the room, raising its temperature by an amount far too small to notice but perfectly real.
Keeping this straight matters because the everyday phrase using up energy is misleading in a way that blocks understanding. Nothing uses energy up. A phone battery that has run flat contains the same total energy it had when charged; what changed is that the energy moved out of a concentrated chemical store and into the dispersed thermal store of the phone and the air around it. The thing that runs out is not energy but concentrated energy, and that distinction is what the rest of this lesson is about. Physicists sometimes make the point by saying that what we buy from an electricity company is not energy but concentration. The energy was already in the coal or the wind; what the system delivers is energy gathered into a form concentrated enough to turn a motor or light a room. Once it has done that job it is still present and no longer concentrated, which is exactly why you cannot run the bill backwards.
Pause and explain
How can energy be conserved and wasted at the same time?
Check your reasoning after answering
Because the two words answer different questions. Conservation says the total amount is unchanged, so the 57 J a filament bulb does not turn into light still exists in the room as a slight warming. Waste says that energy went somewhere it cannot be used. Nothing was destroyed; it was moved into a store too dispersed to be worth collecting.
Part 2 · Efficiency is a fraction
Efficiency is the useful energy out divided by the total energy in, usually written as a percentage. A filament bulb producing 3 J of light for every 60 J supplied is 3 divided by 60, which is 5 per cent. An LED producing 24 J of light for the same 60 J is 40 per cent. An electric kettle is around 90 per cent efficient, which is unusually high and happens for a simple reason: the job you want done is heating, so most of what would count as waste in another device is exactly the output you are paying for.
That last point is worth dwelling on, because efficiency is not a property of a device alone. It depends on what you decide counts as useful. The filament bulb is 5 per cent efficient as a lamp and roughly 95 per cent efficient as a room heater, and both figures describe the same object doing the same thing. When you read an efficiency number anywhere, the first question is always what the person quoting it has counted as the useful output, because changing that definition changes the number without changing the machine. The same question applies to figures you meet outside school. A petrol engine quoted at 30 per cent efficiency is being judged on energy delivered to the wheels, but a figure for the whole journey would also have to count the energy spent refining and transporting the fuel, and that number is lower. Neither is dishonest; they are answers to different questions, and the useful habit is to ask which question was asked.
Pause and explain
The same filament bulb can be described as 5 per cent efficient or 95 per cent efficient. Explain how both can be right.
Check your reasoning after answering
Because efficiency depends on what counts as useful output. Judged as a lamp, only the 3 J of light out of 60 J counts, giving 5 per cent. Judged as a heater, the 57 J of thermal energy is the wanted output, giving about 95 per cent. The device is unchanged; the definition of useful has changed.
Part 3 · Why waste heat stays wasted
Dissipated energy is energy that has spread into the thermal store of the surroundings, and the reason it cannot be recovered is about concentration rather than quantity. The 57 J the bulb releases each second ends up shared among an enormous number of air and wall particles, raising each by an immeasurably small amount. To get useful work back out you would need a temperature difference to drive it, and the whole point is that the energy has levelled out to match everything around it.
A rough comparison makes the scale clear. A room containing about 60 kg of air needs roughly 60,000 J to raise its temperature by 1 degree Celsius. A filament bulb left on for an hour delivers around 216,000 J, so in a sealed room it could warm the air by perhaps 3 degrees Celsius. Spread over the walls, furniture and the air leaking out of the room, the actual rise is far smaller, and no device could usefully collect a fraction of a degree spread through a whole room. This one-way tendency is a genuine law of nature rather than an engineering shortcoming. Concentrated energy spreads out by itself and never gathers itself back up, which is why a cup of tea cools to room temperature and a room-temperature cup never spontaneously heats itself while chilling the room. You can move energy back into a concentrated store, as a refrigerator does, but only by spending more concentrated energy elsewhere to do it.
Pause and explain
Why can the thermal energy released by a light bulb not be collected and used again?
Check your reasoning after answering
Because it has been spread out rather than destroyed. Getting useful work from thermal energy requires a temperature difference, and dissipation means the energy has levelled out to match the surroundings. A few hundred thousand joules shared across a room's air and walls raises everything by a fraction of a degree, which no device can usefully draw on.
Part 4 · Chains of changes
Most real systems put several transfers in a row, and the losses compound. Consider electricity reaching a filament bulb: a coal power station converts the chemical store of the fuel to electricity at about 35 per cent efficiency, transmission lines deliver perhaps 95 per cent of that to the house, and the bulb converts 5 per cent of what arrives into light. Multiplying the three fractions gives roughly 1.7 per cent of the original fuel energy arriving as light in the room.
That figure explains things a single efficiency cannot. It is why replacing the bulb with an LED saves far more fuel than the lamp's own 60 J per second suggests, since every joule saved at the end of the chain saves many times that at the power station. It is also the reasoning behind choosing where to improve a system: the biggest gain comes from the least efficient stage, which here is the power station and the bulb rather than the wires. The arithmetic also explains a claim that sounds wrong at first: an electric heater is about 100 per cent efficient in the room and still may be a poor way to heat a house. Every joule of electricity becomes heat, so nothing is wasted locally, but roughly three joules of fuel were burned at the power station to deliver one joule to the socket. Where you draw the boundary of the system decides which answer you get, which is the lesson from chapter 1 arriving again.
Pause and explain
A chain runs at 35 per cent, then 95 per cent, then 5 per cent. Where should an engineer look for improvement, and why?
Check your reasoning after answering
At the 5 per cent stage first and the 35 per cent stage second, because the overall efficiency is the product of the three and the smallest fraction limits it most. Improving the 95 per cent transmission step can gain at most a twentieth, while raising the final stage from 5 to 40 per cent multiplies the whole chain's output eightfold.
Apply the whole unit · Compare two engines
A petrol car engine converts about 20% of the chemical energy in its fuel into movement. A modern diesel engine manages about 30%. Each car is given 50,000,000 J of fuel.
Your task
Calculate the useful energy from each, compare them, and say where the rest of the energy goes.
What your response should show
- Calculates 10,000,000 J and 15,000,000 J from the stated percentages
- Expresses the difference as a comparison rather than only a subtraction
- Names the thermal store of exhaust, engine and air as the destination
- Supplies observable evidence for the waste rather than asserting it
Response guidance — after your attempt
Calculate the useful energy delivered by each engine from the 50,000,000 J supplied.
Express the diesel's advantage as a fraction of the petrol engine's output.
State where the wasted energy ends up and give the observable evidence.
At 20% efficiency the petrol engine delivers 20 per cent of 50,000,000 J, which is 10,000,000 J of movement. At 30% the diesel delivers 15,000,000 J. The diesel therefore produces 5,000,000 J more from the same fuel, which is half as much again as the petrol engine, so it would travel roughly 1.5 times as far on one tank. The remaining energy, 40,000,000 J in the petrol case and 35,000,000 J in the diesel, ends up almost entirely in the thermal store of the exhaust gases, the engine block, the coolant and the air, with a small amount as sound. The observable evidence is direct: the exhaust is hot, the bonnet is hot, the radiator exists specifically to carry heat away, and the engine is audible from some distance. Nothing is destroyed, but four fifths of the fuel in the petrol car ends up warming the road and the sky.
Scientific references for this unit
- US Department of Energy: where the energy goes in a petrol or diesel vehicle
- US Energy Information Administration: electricity generation and transmission losses
- US Department of Energy: lighting efficiency, filament bulbs against LEDs
- Institute of Physics: energy dissipation and why waste heat is unrecoverable
Parent / teacher teaching notes
Begin with the literal observation, quantity, or diagram relationship. Ask the learner to explain why the evidence supports the claim, check a relevant unit or boundary, then discuss an alternative. The supplied numbers are illustrative, not real observations. A parent can read aloud and allow a spoken rehearsal before writing. Judge science and evidence rather than political, faith, or family agreement. Use the complete data option whenever an actual procedure is unavailable or unsuitable.
The key idea
Energy is never used up and never created, yet machines still waste it. Both statements are true because waste does not mean destruction: it means energy has spread out into the thermal store of the surroundings, where it is too thinly scattered to do anything useful.
Worked examples
Example 1 · Compare two lighting models
- Divide visible-light output by input.
- Account for the remaining stated energy.
- Keep usefulness and conservation distinct.
Example 2 · Transfer to a different case
- Identify the distinction and conditions in this new case.
- Use the relevant mechanism or quantity; preserve units and the chosen boundary.
- Explain why the answer fits and what further evidence would be needed.
Example 3 · Choose a boundary for conservation · a focused example
- State the literal condition or observation in the example.
- Apply the distinction explained in this teaching part.
- Check whether the claim stays within the given evidence.
Avoid these mistakes
- Misleading claim: Energy that is less useful has been destroyed.
- Misleading claim: Conservation means every individual object must keep the same energy.
- Omitting units, measurement timing, or a model boundary makes the evidence hard to interpret.
- Treating illustrative classroom data as real field measurements or copying a model is not an independent explanation.
Check your understanding
Does stopping mean all energy vanished?
Discuss the answer
No. The energy formerly associated with the motion is transferred or redistributed into other changes and surroundings.
Why is the cup alone not a closed energy account?
Discuss the answer
Energy crosses its boundary to the surroundings. The total account must include that transfer or a larger system.
Could thermal output be useful in a different device?
Discuss the answer
Yes. Usefulness depends on the intended function; conservation is not a judgment about whether the output is desirable.
Can the missing 10 J be declared destroyed?
Discuss the answer
No. Check omitted pathways, stored changes, and measurement uncertainty. The record is incomplete under its stated account.
Sustained scientific explanation and revision
These activities are scheduled in the parent plan. Save a first response, a correction, and the reason for the change in the science notebook.
Activity 1 · Energy Transformations, Conservation & Dissipation · Model and explain
Read Two Cups and One Question and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Energy Transformations, Conservation & Dissipation, study Parts 3–4 and attempt the worked case: Calculate each light fraction and explain a limited recommendation for reading. Explain the steps before opening the model.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
A gives 24 ÷ 120 = 20% as visible light and 96 J in thermal pathways. B gives 30% as visible light and 84 J in thermal pathways. B has a larger modeled light fraction for this purpose, but brightness at the page, price, lifetime, and actual measurements would also matter. Both conserve the stated input energy.
Activity 2 · Energy Transformations, Conservation & Dissipation · Practice, revise and exit
Read Two Cups and One Question and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Energy Transformations, Conservation & Dissipation, complete practice questions 1–6 and both choice checks, then answer independently: A bicycle slows with friction. What larger system would make the account clearer? Save a correction explaining one changed claim or method.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
Include the bicycle, contact surfaces, and surrounding air, or list their energy exchanges. Reduced kinetic energy can become thermal changes and sound without being destroyed.
Words to know
- conservation of energy
- Energy remains accounted for across a complete system and its transfers.
- dissipation
- Energy spreading into less readily useful forms or surroundings for the chosen purpose.
- evidence
- A relevant observation, measurement, or record used to evaluate a claim.
- system boundary
- The chosen limit specifying what is included and which exchanges cross it.
- uncertainty
- A stated limit in measurement or knowledge, distinct from a careless mistake.
In the real world
Hybrid and electric cars are designed to capture the kinetic energy of braking and transform it back into stored electrical energy in the battery, instead of wasting all of it as heat in the brakes.
Exit check
A bicycle slows with friction. What larger system would make the account clearer?
Check your explanation after answering
Include the bicycle, contact surfaces, and surrounding air, or list their energy exchanges. Reduced kinetic energy can become thermal changes and sound without being destroyed.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.
Heat, Temperature & Thermal Energy
Learning goals
- I can explain the difference between temperature and thermal energy with an example.
- I can predict which way energy flows between two objects at different temperatures.
- I can calculate the energy needed to heat a given mass by a given number of degrees.
Readings for this unit
Before this unit
Read the chapter opening and the named observation or diagram. Clarify one word or unit that blocks understanding. Recall the relevant earlier measurement, matter, or energy idea.
Study the unit across three 35–45-minute class sessions. Use the worked examples after an attempt and the supplied records when actual equipment is not available.
A spark from a firework can reach well over 1000 degrees Celsius and lands on your skin without harm. A bath at 40 degrees Celsius, far cooler, will warm you up for twenty minutes. The spark is hotter and the bath carries vastly more energy, because the spark weighs a tiny fraction of a gram and the bath holds 80 kg of water.
Temperature measures the average kinetic energy of the particles, so it tells you how violently each particle is moving and nothing about how many there are. Thermal energy is the total across every particle, so it depends on temperature and on mass together.
Heat is a third thing again, and the word is used loosely in ordinary speech. In this course heat means energy on the move because of a temperature difference. An object does not contain heat; it contains thermal energy, and heat is what flows when it meets something colder.
Build your understanding
Where this fits
The first two lessons of this chapter dealt with energy in general. This one narrows to thermal energy, which is the store almost all waste ends up in, and sorts out three words that are used interchangeably outside science. The next lesson covers the three ways heat travels, and the chapter's design task depends on both.
Use three flexible 40-45-minute sessions: temperature against thermal energy; heat as a flow and thermal equilibrium; specific heat capacity and calculating a temperature change, then the practice set, revision and the exit check. Workshop, review, quiz and exams have separate time.
Part 1 · Hot is not the same as a lot
Put 1 kg of water at 80 degrees Celsius next to 100 kg of water at 20 degrees Celsius and ask which holds more thermal energy. The cooler one does, by a wide margin, because thermal energy counts every particle and there are a hundred times as many of them. The same arithmetic explains the spark: at 1000 degrees Celsius its particles are moving furiously, but there is so little of it that the total energy it can deliver to your skin is tiny, and it cools to body temperature almost instantly on contact. An iceberg at minus 2 degrees Celsius contains an enormous amount of thermal energy by this measure, which sounds strange until you remember that the measure is a total rather than an intensity.
This is why a sentence like the oven is hotter than the kettle tells you less than it seems to. It compares two averages and says nothing about how much energy either could deliver. A domestic oven at 200 degrees Celsius holds a few kilograms of thin air; a kettle at 100 degrees Celsius holds 1.5 kg of water, and the water would scald you badly while you can put your hand into the oven briefly without injury. When you want to know what something can do to another object, mass matters as much as temperature.
Pause and explain
Why can you briefly put a hand inside a 200 degrees Celsius oven but not into a 100 degrees Celsius kettle?
Check your reasoning after answering
Because the oven holds very little mass. Temperature reports the average particle energy, while the energy actually delivered to your skin depends on how many particles make contact. The oven contains thin air of low mass, so it transfers energy slowly, whereas the kettle's 1.5 kg of water carries far more thermal energy and delivers it fast.
Part 2 · Heat flows one way
When two objects at different temperatures touch, energy passes from the hotter to the cooler, always in that direction and never the reverse on its own. The flow continues until both reach the same temperature, a state called thermal equilibrium, at which point energy still passes in both directions but at equal rates, so nothing further changes. A cup of tea left on a table reaches room temperature and stops there; it never continues cooling below the room and warming the air further.
A common way of speaking gets this backwards and is worth correcting. People say that cold gets in when a door is opened, as though cold were a substance that travels. There is no such thing as cold, only less thermal energy: when the door opens, energy leaves the warm room and moves into the colder air outside. The same correction applies to a coat, which does not make you warm but slows the rate at which your own thermal energy escapes, which is why a coat on a snowman keeps it frozen longer rather than melting it. Touch is a poor thermometer for the same reason. A metal railing and a wooden bench outdoors on a cold morning are at the same temperature, yet the metal feels far colder, because it draws energy out of your hand much faster than the wood does. What your skin reports is the rate of energy loss, not the temperature, which is exactly why investigations use a thermometer rather than a finger.
Pause and explain
Why does a coat wrapped around a snowman keep it frozen for longer?
Check your reasoning after answering
Because a coat slows energy transfer in whichever direction it would otherwise run. It does not produce warmth; it reduces the rate at which energy crosses it. Around a person it slows body energy escaping, and around a snowman it slows warmth from the surrounding air reaching the ice, so the snowman melts more slowly rather than faster.
Part 3 · Some substances take more filling
Substances differ enormously in how much energy they need to change temperature, a property called specific heat capacity, measured in joules per kilogram per degree Celsius. Water needs about 4180 J to raise 1 kg by 1 degree Celsius. Iron needs about 450, aluminium about 900, and dry sand around 800. Water is extraordinary in this respect, requiring roughly nine times the energy iron does for the same temperature change, which is why it is used as the coolant in car radiators and central heating systems: it can carry a great deal of energy without becoming dangerously hot.
This single number explains observations across the rest of this course. It is why the sea is still cold in June when the beach is too hot to walk on, since sand needs about 800 J per kilogram per degree and water 4180. It is why a coastal town has milder winters than an inland one at the same latitude, and why a hot water bottle stays useful for hours while a metal hand warmer of the same mass cools quickly. Each of these is the same property seen in a different setting. The figures also explain a safety rule worth knowing. Steam at 100 degrees Celsius causes far worse burns than water at 100 degrees Celsius, even though the temperatures are identical, because condensing steam releases about 2,260,000 J per kilogram as it turns back to liquid before it even begins to cool. Temperature alone would predict the two are equally dangerous, and they are not remotely.
Pause and explain
Dry sand needs about 800 J per kilogram per degree and water about 4180. What does this predict about a beach on a sunny day?
Check your reasoning after answering
That the sand will heat far faster than the sea. The same sunlight falling on both delivers similar energy per square metre, but sand needs roughly a fifth as much energy per kilogram to raise its temperature by one degree, so it climbs quickly while the water barely changes. It also predicts that sand will cool quickly after sunset while the sea stays mild.
Part 4 · Putting a number on it
The energy needed to change a temperature is the mass multiplied by the specific heat capacity multiplied by the temperature change. Heating 0.5 kg of water from 20 degrees Celsius to 100 degrees Celsius is a change of 80 degrees Celsius, so the energy required is 0.5 times 4180 times 80, which comes to 167,200 J. That is why a kettle takes a couple of minutes rather than a couple of seconds: a typical kettle supplies around 2000 J every second, so this calculation predicts about 84 seconds, which is close to what a stopwatch gives.
The same formula run backwards is a measuring tool. If you supply a known amount of energy to a known mass and record the temperature rise, you can calculate the specific heat capacity of whatever you heated, which is how the figures in the table above were obtained in the first place. It also exposes losses honestly: if the kettle takes 110 seconds rather than 84, the extra energy went into heating the kettle itself and the surrounding air, and the gap between prediction and stopwatch measures how much. One detail the formula does not cover, and it matters: this calculation works only while the temperature is actually changing. Once the water reaches 100 degrees Celsius the reading stops rising even though the hob keeps supplying energy, because that energy is now going into turning liquid into steam rather than into speeding particles up. That is the flat part of the graph from chapter 2, and it is why a pan left boiling eventually boils dry.
Pause and explain
A calculation predicts a kettle will boil in 84 s but it actually takes 110 s. What does the difference measure?
Check your reasoning after answering
The energy that did not go into the water. The prediction assumes every joule supplied heats the water alone, while in practice some warms the kettle's own metal and plastic and some escapes to the air as steam and through the walls. The 26 second gap is a measurement of those losses rather than a sign the calculation was wrong.
Apply the whole unit · Heat the water
A pan holds 2.0 kg of water at 15 degrees Celsius. A hob supplies energy at 1500 J every second. Water has a specific heat capacity of about 4180 J per kilogram per degree Celsius.
Your task
Calculate the energy and time needed to bring the water to boiling, and compare with what would really happen.
What your response should show
- Calculates the 85 degree change and the 710,600 J requirement
- Divides by the supply rate to get a time with units
- States that the real time is longer, not shorter, with a reason
- Names two specific destinations for the energy that misses the water
Response guidance — after your attempt
Find the temperature change required and calculate the energy needed.
Calculate how long the hob would take to supply that energy.
Explain why the real time would be longer and name two places the extra energy goes.
The water must rise from 15 degrees Celsius to 100 degrees Celsius, a change of 85 degrees Celsius. The energy needed is 2.0 times 4180 times 85, which is 710,600 J. At 1500 J per second the hob would take 710,600 divided by 1500, which is about 474 seconds, or just under 8 minutes. In reality it would take noticeably longer, perhaps 10 or 11 minutes, because the calculation assumes every joule reaches the water. Some goes into heating the pan itself, which may be a kilogram of steel needing about 450 J per kilogram per degree, and some escapes from the surface as warm air and evaporating steam before boiling begins. A third loss is the hob itself radiating sideways rather than into the pan. The prediction is still useful: it sets the floor below which the time cannot fall, and the gap between it and the stopwatch measures the losses.
Scientific references for this unit
- National Institute of Standards and Technology: specific heat capacity data
- Institute of Physics: temperature, thermal energy and heating
- National Oceanic and Atmospheric Administration: ocean heat content and why water warms slowly
- US Department of Energy: how much energy household appliances use
Parent / teacher teaching notes
Begin with the literal observation, quantity, or diagram relationship. Ask the learner to explain why the evidence supports the claim, check a relevant unit or boundary, then discuss an alternative. The supplied numbers are illustrative, not real observations. A parent can read aloud and allow a spoken rehearsal before writing. Judge science and evidence rather than political, faith, or family agreement. Use the complete data option whenever an actual procedure is unavailable or unsuitable.
The key idea
Temperature tells you how fast the particles in a substance are moving on average; thermal energy tells you how much there is in total. A spark at 1000 degrees Celsius will not warm your bath, because temperature and quantity are different questions.
Worked examples
Example 1 · Interpret two cups
- Compare each temperature with the surroundings.
- Identify amount as an additional factor.
- Avoid inventing a joule value or total-energy ranking.
Example 2 · Transfer to a different case
- Identify the distinction and conditions in this new case.
- Use the relevant mechanism or quantity; preserve units and the chosen boundary.
- Explain why the answer fits and what further evidence would be needed.
Example 3 · Consider amount, material, and state · a focused example
- State the literal condition or observation in the example.
- Apply the distinction explained in this teaching part.
- Check whether the claim stays within the given evidence.
Avoid these mistakes
- Misleading claim: Heat is a material substance stored inside an object.
- Misleading claim: The hotter sample must always have the greater total thermal energy.
- Omitting units, measurement timing, or a model boundary makes the evidence hard to interpret.
- Treating illustrative classroom data as real field measurements or copying a model is not an independent explanation.
Check your understanding
Why are degrees and joules not interchangeable?
Discuss the answer
They measure different quantities: temperature and energy. An additional physical model is needed to connect them numerically.
Does equal temperature mean equal energy totals?
Discuss the answer
No. Amount and material matter. The comparison separates average particle behavior from the whole sample’s energy account.
What happens to the cooler cup?
Discuss the answer
Net energy transfer from the warmer surroundings tends to raise its temperature toward room conditions.
Does reaching room temperature mean no particle motion?
Discuss the answer
No. Microscopic motion continues; equilibrium concerns the absence of a net temperature-driven transfer between the compared systems.
Sustained scientific explanation and revision
These activities are scheduled in the parent plan. Save a first response, a correction, and the reason for the change in the science notebook.
Activity 1 · Heat, Temperature & Thermal Energy · Model and explain
Read Two Cups and One Question and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Heat, Temperature & Thermal Energy, study Parts 3–4 and attempt the worked case: Predict the net transfer direction for each and explain why temperature alone cannot rank their total energy. Explain the steps before opening the model.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
Both cups are warmer than the room, so net heat transfer tends outward and they cool. A has the higher temperature, while B contains more water. Without a stated energy model and reference, these readings alone do not justify a complete numerical total-energy comparison. Degrees Celsius cannot simply be relabeled as joules.
Activity 2 · Heat, Temperature & Thermal Energy · Practice, revise and exit
Read Two Cups and One Question and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Heat, Temperature & Thermal Energy, complete practice questions 1–6 and both choice checks, then answer independently: A thermometer reads 0 °C in ice water. Have its particles stopped moving? Save a correction explaining one changed claim or method.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
No. Zero on the Celsius scale is not zero microscopic motion. The reading describes a temperature under that scale, not the absence of energy.
Words to know
- temperature
- A property related to average microscopic particle motion in a simple material model.
- heat
- Energy transfer caused by a temperature difference.
- evidence
- A relevant observation, measurement, or record used to evaluate a claim.
- system boundary
- The chosen limit specifying what is included and which exchanges cross it.
- uncertainty
- A stated limit in measurement or knowledge, distinct from a careless mistake.
In the real world
Weather forecasters track the huge amount of thermal energy stored in oceans and lakes, because that stored energy is released slowly and keeps nearby towns from getting as hot or as cold as places far inland.
Exit check
A thermometer reads 0 °C in ice water. Have its particles stopped moving?
Check your explanation after answering
No. Zero on the Celsius scale is not zero microscopic motion. The reading describes a temperature under that scale, not the absence of energy.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.
Conduction, Convection & Radiation
Learning goals
- I can explain why metals conduct far better than air or wood.
- I can explain how a convection current forms from a density change.
- I can explain how radiation differs from the other two and what surfaces affect it.
Readings for this unit
Before this unit
Read the chapter opening and the named observation or diagram. Clarify one word or unit that blocks understanding. Recall the relevant earlier measurement, matter, or energy idea.
Study the unit across three 35–45-minute class sessions. Use the worked examples after an attempt and the supplied records when actual equipment is not available.
Thermal conductivity measures how readily a material passes energy along, and the range is enormous. Copper is about 400 watts per metre per degree Celsius, steel about 50, glass about 1, water about 0.6, wood around 0.15 and still air only 0.026. Copper carries energy roughly fifteen thousand times better than air does.
That single table explains most insulation. Wool, fibreglass, feathers and expanded polystyrene are not good insulators because of what they are made of but because of what they trap: still air, in pockets small enough that the air cannot circulate. The material is mostly a scaffold for holding air still.
Conduction is only one of the three routes, though. A fluid can carry energy bodily by moving, which is convection, and energy can cross a complete vacuum as infrared radiation, which is how it reaches Earth from the Sun across about 150 million km.
Build your understanding
Where this fits
The last lesson established what thermal energy is and which way it flows. This one is about how it gets there, and it supplies everything needed for the chapter's design task, where you will try to keep something warm and then explain which of the three routes your design actually blocked.
Use three flexible 40-45-minute sessions: conduction and why metals differ from air; convection currents and density; radiation, surfaces and the vacuum flask, then the practice set, revision and the exit check. Workshop, review, quiz and exams have separate time.
Part 1 · Conduction: handed along
Heat one end of a metal rod and the particles there vibrate harder, knock into their neighbours and set them vibrating too, and the disturbance travels along without the particles themselves going anywhere. That is conduction, and it works in solids, liquids and gases, but far better in solids because the particles are close enough to keep hitting each other. Metals are better still, by a wide margin, because they contain electrons that are free to move through the whole structure rather than being tied to individual atoms, and those electrons carry energy from end to end far faster than vibration alone could manage.
The numbers make the point sharply. Copper at about 400 W per metre per degree Celsius against still air at 0.026 is a factor of about fifteen thousand, which is why a metal spoon left in hot soup becomes too hot to hold in under a minute while a wooden one stays comfortable. It is also why the handles of good saucepans are wood or plastic at around 0.15 to 0.2, and why a double-glazed window works: the gap between the panes is not empty but filled with still air or argon, and the insulating layer is the gas, not the extra glass. Animals arrived at the same solution long before engineers did. A bird fluffs its feathers in cold weather to thicken the layer of trapped air next to its skin, a sheep's fleece works the same way, and a polar bear's hollow hairs each enclose their own column of still air. In every case the insulating substance is air at 0.026 W per metre per degree Celsius, and the biology is a mechanism for holding it in place.
Pause and explain
Why is still air one of the best insulators available when a breeze feels so cold?
Check your reasoning after answering
Because still air conducts very poorly, at about 0.026 W per metre per degree Celsius, so it passes almost no energy along by particle contact. A breeze feels cold because moving air carries energy away bodily by convection and replaces warmed air with fresh cold air, which is a different mechanism. Insulators work by holding air still so that convection cannot happen.
Part 2 · Convection: the fluid carries it
Warm a region of a liquid or gas and its particles move apart slightly, so that portion becomes less dense than the fluid around it and floats upward, exactly as the cork floated on water in chapter 2. Cooler, denser fluid sinks to take its place, is warmed in turn, and rises; the result is a continuous loop called a convection current. The energy is being carried by the fluid physically moving, not passed along a chain of stationary particles, which is why convection cannot happen in a solid at all.
This is doing more work around you than conduction is. A household radiator is named badly: it warms a room mostly by setting up a convection current, drawing cool air across the floor, warming it, and sending it up the wall and across the ceiling. The same process makes a hot air balloon rise, drives the sea breeze described in chapter 2, and in chapter 6 will turn out to drive weather on a continental scale. It is also why a freezer compartment sits at the top of an older fridge, so that the cold dense air it produces sinks through the rest of the cabinet. You can watch a convection current directly with very little equipment. Drop a crystal of potassium permanganate into a beaker of water and heat one corner gently: a coloured ribbon rises from the heated spot, travels across the surface, sinks at the far side and returns along the bottom, tracing the whole loop. What the dye shows is water physically moving, which is the entire difference between convection and the conduction in the previous section.
Pause and explain
Why can convection happen in air and water but never in a solid?
Check your reasoning after answering
Because convection requires the material itself to move. Warmed fluid expands, becomes less dense and floats upward while cooler fluid sinks to replace it, which depends on particles being free to change places. In a solid the particles are locked in a fixed arrangement and can only vibrate, so energy must be passed along by conduction instead.
Part 3 · Radiation: across nothing at all
Every object emits infrared radiation, and the hotter it is the more it emits. Unlike the other two routes this one needs no material whatever, which is how energy crosses about 150 million km of vacuum from the Sun to Earth in a little over eight minutes. You can feel the difference directly: standing beside a bonfire, the side of your face towards the flames is warmed instantly even though the air between is barely moving, and stepping behind someone blocks it at once, because radiation travels in straight lines and can be cast into shadow.
Surfaces matter here in a way they do not for conduction. Matt black surfaces are the best absorbers of infrared and also the best emitters, while shiny silvered surfaces are poor at both and reflect instead. This is why solar water heating panels are painted matt black, why the cooling fins on the back of an old fridge are black, and why emergency blankets are shiny: wrapping someone in reflective foil throws their own infrared back at them instead of letting it radiate away into the night. Radiation also explains a measurement you can make on any clear night. A car parked under open sky often has frost on its roof when the air temperature never fell below 2 or 3 degrees Celsius, because the roof radiates infrared upward into space and cools below the air around it. A car parked under a tree or a carport usually has none, since the cover radiates back down and the roof loses far less.
Pause and explain
Why are solar panels matt black while emergency blankets are shiny?
Check your reasoning after answering
Because the two need opposite properties. A matt black surface absorbs infrared radiation well, so a solar panel painted that way captures as much of the Sun's energy as possible. A shiny surface reflects infrared rather than absorbing or emitting it, so a reflective blanket turns a person's own radiated energy back towards them instead of letting it escape.
Part 4 · Beating all three at once
A vacuum flask is worth studying because it is a deliberate attack on each route in turn, and no single feature would be enough. Conduction is blocked by a double wall with the air pumped out between the layers, since with no particles in the gap there is nothing to pass energy along. Convection is blocked by the same vacuum, because a current needs a fluid to circulate and there is none. Radiation is blocked by silvering both facing surfaces, so infrared leaving the inner wall is reflected straight back instead of crossing the gap.
What remains is the small amount of conduction through the stopper and the thin neck of glass where the two walls join, which is why a flask does eventually cool and why the stopper is made of plastic or cork rather than metal. Working out which route a design blocks, and which it leaves open, is exactly the analysis the chapter's design task asks for. A container that is well insulated against conduction but left open at the top has solved one problem and ignored the convection current carrying energy straight out of it. It is worth noticing how much of the flask's performance comes from the vacuum rather than from any clever material. With no particles between the walls, two of the three routes are not merely slowed but eliminated, which is something no solid insulator can achieve at any thickness. That is why a good flask keeps a drink hot for several hours while a thick woollen cosy of the same bulk manages perhaps thirty minutes.
Pause and explain
A vacuum flask has silvered walls as well as a vacuum. Why is the vacuum alone not enough?
Check your reasoning after answering
Because a vacuum stops conduction and convection but not radiation, which needs no material to travel through. Infrared would cross the empty gap unhindered and carry energy from the inner wall to the outer one. Silvering both facing surfaces reflects that radiation back, closing the third route the vacuum leaves wide open.
Apply the whole unit · Explain the design
A takeaway coffee cup is made of corrugated card around a thin plastic-lined paper wall, with a plastic lid that has a small drinking hole. The coffee starts at 85 degrees Celsius.
Your task
Identify which transfer route each feature addresses and name the weakness in the design.
What your response should show
- Links the corrugated card to conduction and explains that trapped air does the work
- Links the lid to convection with a reason, not just an assertion
- Identifies radiation as the unaddressed route
- Proposes an improvement that targets the route actually named
Response guidance — after your attempt
Say which route the corrugated card wall mainly blocks and how it does so.
Say which route the lid mainly blocks and give your reason.
Identify the route the design handles worst and suggest one improvement.
The corrugated card blocks conduction. Its value is not the card itself but the air trapped in the flutes, which at about 0.026 W per metre per degree Celsius conducts about fifteen thousand times worse than copper, and the corrugations keep that air still so convection cannot start within it. The lid blocks convection: without it, hot air and steam would rise continuously off the surface and be replaced by cool air, carrying energy away quickly, which is the fastest loss from an open cup. The route handled worst is radiation, since nothing in the cup is reflective and both card and plastic emit infrared freely from the outer surface. An improvement would be a thin reflective foil layer between the card and the paper wall, which is what the better flasks do and would cost very little. A second weakness is the drinking hole in the lid, which leaves a small convection path open by design, and that one cannot be fixed without making the cup unusable.
Scientific references for this unit
- National Institute of Standards and Technology: thermal conductivity reference data
- Institute of Physics: conduction, convection and radiation in the classroom
- US Department of Energy: home insulation and how trapped air works
- NASA: infrared radiation and how energy crosses space
Parent / teacher teaching notes
Begin with the literal observation, quantity, or diagram relationship. Ask the learner to explain why the evidence supports the claim, check a relevant unit or boundary, then discuss an alternative. The supplied numbers are illustrative, not real observations. A parent can read aloud and allow a spoken rehearsal before writing. Judge science and evidence rather than political, faith, or family agreement. Use the complete data option whenever an actual procedure is unavailable or unsuitable.
The key idea
Energy moves from hot to cold by three distinct routes: passed along between touching particles, carried bodily by a moving fluid, or beamed across space as infrared. A vacuum flask works because it blocks all three at once, and nothing less would do.
Worked examples
Example 1 · Three pathways around a warm cup
- Identify matter interactions at the wall.
- Identify moving fluid around the cup.
- Describe radiation and a bounded insulation claim.
Example 2 · Transfer to a different case
- Identify the distinction and conditions in this new case.
- Use the relevant mechanism or quantity; preserve units and the chosen boundary.
- Explain why the answer fits and what further evidence would be needed.
Example 3 · Explain convection as fluid motion · a focused example
- State the literal condition or observation in the example.
- Apply the distinction explained in this teaching part.
- Check whether the claim stays within the given evidence.
Avoid these mistakes
- Misleading claim: All heat always rises regardless of the transfer mechanism.
- Misleading claim: Radiation requires air or water between source and receiver.
- Omitting units, measurement timing, or a model boundary makes the evidence hard to interpret.
- Treating illustrative classroom data as real field measurements or copying a model is not an independent explanation.
Check your understanding
Did metal have to move along the handle?
Discuss the answer
No. Energy transfers through interactions within the material; bulk transport of the handle is not required.
How is convection different from conduction?
Discuss the answer
Convection includes bulk fluid motion carrying energy. Conduction transfers energy through local interactions without that bulk motion.
Why can sunlight transfer energy through space?
Discuss the answer
Radiation does not require a material medium between source and receiver.
Does insulation prove no heat transfer occurs?
Discuss the answer
No. It can reduce transfer rates under the stated design while other pathways and imperfections remain.
Sustained scientific explanation and revision
These activities are scheduled in the parent plan. Save a first response, a correction, and the reason for the change in the science notebook.
Activity 1 · Conduction, Convection & Radiation · Model and explain
Read Two Cups and One Question and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Conduction, Convection & Radiation, study Parts 3–4 and attempt the worked case: Explain all three pathways and what a fitted sleeve might change. Explain the steps before opening the model.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
Conduction transfers energy through the wall; moving air can carry energy by convection; infrared radiation exchanges energy with surroundings. A sleeve can reduce some transfer through the wall and alter airflow, depending on its design. It does not guarantee zero cooling or prevent radiation by definition.
Activity 2 · Conduction, Convection & Radiation · Practice, revise and exit
Read Two Cups and One Question and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Conduction, Convection & Radiation, complete practice questions 1–6 and both choice checks, then answer independently: An object is warmed from the side by radiation. Must the energy move upward? Save a correction explaining one changed claim or method.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
No. Radiation can travel in many directions. Rising warm fluid is a separate situation involving convection and buoyancy.
Words to know
- convection
- Energy transport associated with bulk motion of a liquid or gas.
- radiation
- Energy transfer by electromagnetic waves, which can cross empty space.
- evidence
- A relevant observation, measurement, or record used to evaluate a claim.
- system boundary
- The chosen limit specifying what is included and which exchanges cross it.
- uncertainty
- A stated limit in measurement or knowledge, distinct from a careless mistake.
In the real world
Winter coats trap a thick layer of still air — a good insulator — to slow conduction and convection, keeping your body heat from escaping, while a shiny emergency blanket reflects radiated heat back toward you.
Exit check
An object is warmed from the side by radiation. Must the energy move upward?
Check your explanation after answering
No. Radiation can travel in many directions. Rising warm fluid is a separate situation involving convection and buoyancy.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.
Thermal Design: Compare, Improve & Retest
Learning goals
- I can state a design goal as a measurable criterion before building anything.
- I can test two prototypes fairly and say which performed better.
- I can explain why only one feature should change between versions.
Readings for this unit
Before this unit
Read the chapter opening and the named observation or diagram. Clarify one word or unit that blocks understanding. Recall the relevant earlier measurement, matter, or energy idea.
Study the unit across three 35–45-minute class sessions. Use the worked examples after an attempt and the supplied records when actual equipment is not available.
A vague goal produces a vague result. Keep the water warm cannot be judged, because warm is not a quantity and keep is not a duration. Lose no more than 15 degrees Celsius in 20 minutes, starting from 80 degrees Celsius, can be judged by anyone with a thermometer and a timer, and two designs can be ranked against it.
The number also tells you when to stop. A design that loses 12 degrees Celsius has met the criterion and further work on it is optional; a design that loses 31 degrees Celsius has not, and you now know by how much it fell short rather than only that it felt disappointing.
The rest of this lesson is the testing discipline from chapter 1 applied to building things. One thing changes between versions, everything else is held steady, and each version is measured the same way so that the comparison means something.
Build your understanding
Where this fits
This lesson closes the energy chapter by putting the three transfer routes to work. Everything you need is already in place: conduction, convection and radiation from the last lesson, specific heat capacity from the one before, and fair testing from chapter 1. What is new is the cycle of build, measure, change one thing, measure again.
Use three flexible 40-45-minute sessions: turning a goal into a criterion; testing two prototypes fairly; iterating and weighing trade-offs, then the practice set, revision and the exit check. Workshop, review, quiz and exams have separate time.
Part 1 · Write the criterion first
Before any material is cut, decide how the finished thing will be judged, and write it as a sentence containing numbers. A usable criterion names the starting condition, the quantity measured, the limit and the time: starting with 200 mL of water at 80 degrees Celsius in a room at 20 degrees Celsius, the container must lose no more than 15 degrees Celsius in 20 minutes. Everything in that sentence is checkable by someone who was not there, which is the test of whether a criterion is doing its job.
Constraints belong in the specification too, because a design that meets the criterion by ignoring every practical limit has not solved the problem. Realistic constraints for a classroom task might be a budget of five materials, a finished size that still fits in a bag, and a lid that can actually be opened to drink from. Writing these down at the start prevents the commonest outcome of an unconstrained design task, which is a beautifully insulated block that nobody could carry or drink out of and that therefore answers a question nobody asked. It is worth deciding in advance how you will record the test as well. A table with a row for each version and columns for start temperature, end temperature, drop, materials used and cost takes two minutes to rule and makes the comparison obvious at a glance. Without it, results accumulate as scattered notes and by the fourth version nobody can remember which cup had which lining.
Pause and explain
Why is 'keep the water warm' not usable as a design criterion?
Check your reasoning after answering
Because neither word is measurable. Warm names no temperature and keep names no duration, so two people testing the same container could reach opposite verdicts and neither could be shown wrong. A criterion such as losing no more than 15 degrees Celsius in 20 minutes from a start of 80 can be checked by anyone with a thermometer and a timer.
Part 2 · Make the comparison fair
Comparing two containers is an investigation, so the rules from chapter 1 apply without modification. The independent variable is the design; the dependent variable is the temperature drop in degrees Celsius over the fixed period; everything else is a controlled variable and there are more of them than students expect. Both containers need the same volume of water, the same starting temperature, the same room, the same thermometer, lids on or off consistently, and measurements taken at the same intervals.
Two controls catch most of the errors in this particular task. The first is the room: a container tested beside a sunny window will beat an identical one tested in a draught, and the difference measures the position rather than the design. The second is starting temperature, because a container starting at 85 degrees Celsius loses energy faster than one starting at 75, since the rate of transfer depends on the difference between inside and outside. Pour both from the same kettle at the same moment and the problem disappears. Taking readings along the way rather than only at the end is also worth the trouble. A reading every 5 minutes gives you a cooling curve instead of a single number, and the shape carries information the endpoint hides: a container that loses 10 degrees Celsius in the first 5 minutes and then almost nothing has a different problem from one that loses 3 degrees Celsius every 5 minutes steadily. The first suggests a gap somewhere, the second suggests the whole wall is too thin.
Pause and explain
Why must both prototypes start at the same water temperature?
Check your reasoning after answering
Because the rate of energy transfer depends on the temperature difference between the water and the room. A container starting at 85 degrees Celsius loses energy faster than one starting at 75, so a design given the hotter start is penalised for something that has nothing to do with its insulation. Pouring both from the same kettle at once removes the problem.
Part 3 · One change at a time
The temptation after a disappointing first test is to rebuild everything, and it is the single most common way a design project stops producing information. If version two has a foil lining, a thicker wall and a new lid, and it loses 9 degrees Celsius where version one lost 24, you have learned that the combination works and nothing whatever about which part earned the improvement. You cannot drop the expensive feature, because you do not know whether it was the one doing the work.
Changing one feature per version is slower per round and far faster overall. Add the foil alone and retest: a drop from 24 to 18 degrees Celsius attributes 6 degrees to blocking radiation. Then add the thicker wall and retest: 18 to 13 attributes 5 degrees to reducing conduction. Now you have a ranked list of what each change bought, you can say which route each one blocked, and if the budget allows only one feature you know which to keep. There is a limit to this patience that is worth naming honestly. Each round of testing takes 20 minutes plus setting up, so four versions is most of a lesson and eight is not realistic. When time is short, the sensible compromise is to change one feature at a time for the features you are unsure about, and to accept bundling together the ones you are confident act on different transfer routes. What you must not do is bundle changes and then report a conclusion about one of them.
Pause and explain
Version two changes three features at once and performs much better. What has the test failed to tell you?
Check your reasoning after answering
Which of the three changes produced the improvement, and whether any of them helped at all. One feature might account for the entire gain while another does nothing or even makes things slightly worse, and the combined result hides this. It also means the design cannot be simplified or made cheaper, because no feature can safely be removed.
Part 4 · What you give up
The best-performing design is rarely the best design, because performance is only one of the things being judged. A container with 10 cm of insulation on every side will keep water hot for hours and will not fit in a bag, cannot be washed easily and may cost more than anyone would pay. Engineering decisions are nearly always a trade between performance, cost, size, weight, durability and how pleasant the thing is to use, and a design report that mentions only the temperature drop has reported on one axis out of six.
A useful way to weigh these is to express improvement against cost. If a foil lining costs 20 p and saves 6 degrees Celsius, that is 3.3 p per degree; if a second layer of card costs 50 p and saves 2 degrees, that is 25 p per degree, roughly eight times worse value. Figures like these turn an argument about which feature is better into a comparison anyone can check, and they often show that the cheap, unglamorous change is the one worth keeping. The same calculation is what decides real insulation projects. Loft insulation in a house is usually fitted before wall insulation and before triple glazing, not because it performs best in absolute terms but because it costs least per degree retained, and a given budget saves more energy spread across the cheap measures than spent on the impressive one. Engineers call this value engineering, and it is the reason the best-performing option on a test bench often loses.
Pause and explain
Why might a design that performs best in testing still be rejected?
Check your reasoning after answering
Because performance is one criterion among several. A container insulated thickly enough to win on temperature may be too bulky to carry, too expensive, hard to clean or awkward to drink from, and those constraints were part of the problem from the start. A design is judged against the whole specification, not against the single quantity that happens to be easiest to measure.
Apply the whole unit · Judge two prototypes
Two containers each start with 200 mL of water at 80 degrees Celsius in a room at 20 degrees Celsius. After 20 minutes, A reads 61 degrees Celsius and B reads 68 degrees Celsius. A is a card cup with a lid; B is the same cup with a foil lining added and no lid. The criterion was to lose no more than 15 degrees Celsius.
Your task
Decide which design is better, state what the test does not establish, and plan the next version.
What your response should show
- Calculates both drops and compares each against the 15 degree criterion
- Identifies that two variables differ between the prototypes
- Reasons about which route each feature affects rather than only ranking them
- Specifies a next version that changes exactly one feature
Response guidance — after your attempt
Calculate each temperature drop and say which designs met the criterion.
Identify the problem with attributing B's performance to the foil.
Describe the next prototype and the single change it should make.
A dropped 80 minus 61, which is 19 degrees Celsius, and B dropped 80 minus 68, which is 12 degrees Celsius. B met the criterion of no more than 15 and A missed it by 4 degrees Celsius. B is better on the measured criterion, but the test cannot tell you why, because two features differ at once: B gained a foil lining and also lost its lid. Those should pull in opposite directions, since the foil blocks radiation while removing the lid opens a convection path, so B may be performing well despite the missing lid rather than because of it, and the foil's true contribution could be larger than 7 degrees Celsius. The next prototype should be the foil-lined cup with the lid put back on, changing exactly one thing from B. If that version drops only 7 or 8 degrees Celsius, the lid is worth about 4 or 5 degrees and both features earn their place.
Scientific references for this unit
- US Department of Energy: insulation performance and measuring R-values
- National Institute of Standards and Technology: engineering measurement and test design
- Institute of Physics: investigating thermal insulation in the classroom
- NASA: thermal protection design and the trade-offs engineers accept
Parent / teacher teaching notes
Begin with the literal observation, quantity, or diagram relationship. Ask the learner to explain why the evidence supports the claim, check a relevant unit or boundary, then discuss an alternative. The supplied numbers are illustrative, not real observations. A parent can read aloud and allow a spoken rehearsal before writing. Judge science and evidence rather than political, faith, or family agreement. Use the complete data option whenever an actual procedure is unavailable or unsuitable.
The key idea
Designing something that keeps heat in is a measurement problem before it is a building problem. Until success is defined as a number, there is no way to tell whether version two is better than version one, and no way to know which change was responsible.
Worked examples
Example 1 · Recommend within a constraint
- Average each set of comparable trials.
- Apply performance and cost conditions together.
- Name a redesign or repeat with a method limit.
Example 2 · Transfer to a different case
- Identify the distinction and conditions in this new case.
- Use the relevant mechanism or quantity; preserve units and the chosen boundary.
- Explain why the answer fits and what further evidence would be needed.
Example 3 · Design a matched comparison · a focused example
- State the literal condition or observation in the example.
- Apply the distinction explained in this teaching part.
- Check whether the claim stays within the given evidence.
Avoid these mistakes
- Misleading claim: The largest performance result automatically wins regardless of constraints.
- Misleading claim: A changed design can inherit the old design’s measured results without retesting.
- Omitting units, measurement timing, or a model boundary makes the evidence hard to interpret.
- Treating illustrative classroom data as real field measurements or copying a model is not an independent explanation.
Check your understanding
Why state the budget before ranking designs?
Discuss the answer
It defines which designs are feasible. Choosing a performance winner first and ignoring its cost changes the original problem.
Can those final readings isolate sleeve quality?
Discuss the answer
No. Use matched starts and compare drops over the same interval before attributing the difference to the sleeves.
Which design fits the stated cost constraint?
Discuss the answer
A fits the limit. B performs better in the modeled temperature measure but is not feasible under that constraint unless it is redesigned.
Why can’t the redesign automatically use the old temperature drops?
Discuss the answer
Changing the feature can change heat-transfer rates. The new design must be tested under its own stated conditions.
Sustained scientific explanation and revision
These activities are scheduled in the parent plan. Save a first response, a correction, and the reason for the change in the science notebook.
Activity 1 · Thermal Design: Compare, Improve & Retest · Model and explain
Read Two Cups and One Question and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Thermal Design: Compare, Improve & Retest, study Parts 3–4 and attempt the worked case: Calculate the means, recommend a feasible design, and propose a next test. Explain the steps before opening the model.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
C has mean drop 6 °C and costs 3 tokens, meeting both stated conditions. D has mean 4 °C but exceeds the budget. Recommend C for this modeled problem, while noting its 5–7 °C spread and repeating to check consistency. A cheaper D variant would need its own fair test.
Activity 2 · Thermal Design: Compare, Improve & Retest · Practice, revise and exit
Read Two Cups and One Question and the linked unit teaching; use its complete supplied case and diagrams.
Your task
For Thermal Design: Compare, Improve & Retest, complete practice questions 1–6 and both choice checks, then answer independently: A design reaches the best temperature in one trial but cannot fit the cup. Is it necessarily the best solution? Save a correction explaining one changed claim or method.
Success criteria
- An accurate scientific claim answering the actual question.
- Relevant evidence or a labeled model with quantities and units when applicable.
- Reasoning that connects evidence with the mechanism rather than only repeats it.
- A specific method, boundary, scale, or alternative-explanation limit.
Hint
Begin with the actual observation, quantity, or diagram relationship. Explain how it bears on the question before making a broad claim.
Response guidance — discuss after your attempt
No. Fit is a constraint, and one trial does not establish reliable performance. Evaluate all stated requirements and repeat a suitable design.
Words to know
- criterion
- A stated measure of desired success in a design problem.
- constraint
- A limit that the proposed solution must satisfy.
- evidence
- A relevant observation, measurement, or record used to evaluate a claim.
- system boundary
- The chosen limit specifying what is included and which exchanges cross it.
- uncertainty
- A stated limit in measurement or knowledge, distinct from a careless mistake.
In the real world
Exit check
A design reaches the best temperature in one trial but cannot fit the cup. Is it necessarily the best solution?
Check your explanation after answering
No. Fit is a constraint, and one trial does not establish reliable performance. Evaluate all stated requirements and repeat a suitable design.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.
Problem 1
Answer and explanation
The modeled 100 J transfers into 25 J light and 75 J thermal pathways. Mass in grams describes matter, while a temperature reading in °C is not an energy total. The unchanged casing mass does not mean no energy transfer occurred, and this illustrative partition is not a measurement of every flashlight.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 2
Answer and explanation
Gravitational potential energy relative to a common reference. The higher book has greater potential energy in the book–Earth system under matched mass and gravity conditions.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 3
Answer and explanation
A gives 24 ÷ 120 = 20% as visible light and 96 J in thermal pathways. B gives 30% as visible light and 84 J in thermal pathways. B has a larger modeled light fraction for this purpose, but brightness at the page, price, lifetime, and actual measurements would also matter. Both conserve the stated input energy.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 4
Answer and explanation
Include the bicycle, contact surfaces, and surrounding air, or list their energy exchanges. Reduced kinetic energy can become thermal changes and sound without being destroyed.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 5
Answer and explanation
Both cups are warmer than the room, so net heat transfer tends outward and they cool. A has the higher temperature, while B contains more water. Without a stated energy model and reference, these readings alone do not justify a complete numerical total-energy comparison. Degrees Celsius cannot simply be relabeled as joules.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 6
Answer and explanation
No. Zero on the Celsius scale is not zero microscopic motion. The reading describes a temperature under that scale, not the absence of energy.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 7
Answer and explanation
Conduction transfers energy through the wall; moving air can carry energy by convection; infrared radiation exchanges energy with surroundings. A sleeve can reduce some transfer through the wall and alter airflow, depending on its design. It does not guarantee zero cooling or prevent radiation by definition.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 8
Answer and explanation
No. Radiation can travel in many directions. Rising warm fluid is a separate situation involving convection and buoyancy.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 9
Answer and explanation
C has mean drop 6 °C and costs 3 tokens, meeting both stated conditions. D has mean 4 °C but exceeds the budget. Recommend C for this modeled problem, while noting its 5–7 °C spread and repeating to check consistency. A cheaper D variant would need its own fair test.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 10
Answer and explanation
No. Fit is a constraint, and one trial does not establish reliable performance. Evaluate all stated requirements and repeat a suitable design.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.