The big idea: A justified material choice is a chain of four: the requirement, the property it demands, the evidence for that property, and the trade-off you accepted.
The evidence link is the one students skip — and without it a choice is a preference, however confidently it is written.
Three worked lines from one product, then where the evidence comes from.
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Secondary — published
- Material property tables: strength, modulus, density
- Corrosion resistance charts and compatibility tables
- Standards and regulations the product must meet
- Supplier data sheets — which must be corroborated
- Gives you numbers you could never measure yourself
Primary — your own testing
- A drop test on three candidate seat panels
- A slip-angle test on the real floor, wet and dry
- 200 wipes with the cleaner actually used in the lab
- Asking users which surface they would rather sit on
- Tells you about THIS material in THIS environment
Neither replaces the other: Published data cannot know your floor, your cleaner or your loads. Your own tests cannot span a whole population of materials.
The strongest justification cites both — and corroborates any supplier claim against an independent source, because the supplier gains if you believe it.
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| Requirement | Property | Evidence | Trade-off accepted |
|---|---|---|---|
| Seat carries a student who drops onto it | Stiffness and impact strength | Own drop test on 3 samples, plus published plywood stiffness data | Heavier than moulded polymer, but repairable in the workshop |
| Frame survives daily mopping and acid splashes | Corrosion resistance to water and dilute acids | Supplier data sheet corroborated against a published corrosion table | Stainless costs more per metre than coated mild steel |
| Feet do not slide on sealed vinyl | Coefficient of friction, wet and dry | Own slip-angle test on the real floor, 3 candidate compounds | The grippiest compound marked the floor, so the second best was used |
Two failures that cost most of the marks: No evidence. "Stainless steel was chosen because it does not rust" is a claim with no source and no number.
No trade-off. A justification that lists only advantages reads as a sales pitch. Say what you gave up, and why it was worth it.
Cite it properly: A property you took from somewhere must say where — publication, table, supplier and date. A test you ran must say how many samples, under what conditions, and what you measured.
An uncited figure carries no weight, because nobody can check it.
How this is tested — justifying a material choice using primary and secondary research. It comes up two ways:
Paper 1 — multiple choice
- Identify whether stated evidence is primary or secondary.
- Pick the justification that is evidenced rather than asserted.
Paper 2 — analysing a product
- Justify a material choice for a named product using research.
- Explain why a supplier data sheet must be corroborated.
The trap: Writing advantages with no source and no trade-off. Every justified choice needs a number, where the number came from, and what you accepted in exchange.
Justify the choice of stainless steel for the frame of a science-lab stool, using primary and secondary research.
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