Thermal Design: Compare, Improve & Retest · Grade 6 Science
Chapter: Energy, Heat & Thermal DesignThermal 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.