Scientists do not simply guess — they argue using evidence. A strong scientific argument connects a clear claim to reliable evidence through sound reasoning. In this lesson you will learn the claim-evidence-reasoning (CER) framework, practise evaluating sources for reliability and bias, and craft your own evidence-based conclusions about waves and motion phenomena. These skills are essential for your depth study and for thinking like a scientist in any field.
Imagine two students disagree about whether seatbelts should be compulsory in all school buses.
Write down your answers before reading on:
Building scientific arguments that stand up to scrutiny
Every strong scientific argument has three essential parts. Think of them as the骨架 (skeleton),肌肉 (muscle) and heartbeat of scientific thinking:
The claim is a clear, concise statement that answers the question. It must be specific and testable. A weak claim is vague: "Forces are important." A strong claim is precise: "According to Newton's third law, the forward force a swimmer exerts on the water is matched by an equal backward force the water exerts on the swimmer, which propels the swimmer forward."
The evidence is the data or observations that support the claim. Evidence must come from reliable sources — peer-reviewed journals, reputable scientific institutions, well-designed experiments or reputable data repositories. One strong piece of evidence is better than five weak ones.
The reasoning is the bridge between evidence and claim. It explains why the evidence supports the claim, using scientific principles. Without reasoning, evidence is just a list of facts. With reasoning, evidence becomes a compelling argument.
Not all evidence is created equal
Before you use evidence in an argument, you must evaluate its source. Scientists use a set of criteria to judge whether a source is trustworthy:
| Criterion | What to ask | Green flag | Red flag |
|---|---|---|---|
| Authority | Who wrote this? What are their qualifications? | Expert in the field, affiliated with a recognised institution | No author listed, no relevant expertise |
| Currency | When was this published? Is the science up to date? | Recent publication, references current research | Outdated data, no publication date |
| Purpose | Why was this written? To inform, sell or persuade? | Objective, educational or research purpose | Advertisement, sensational headline, hidden agenda |
| Evidence base | Does the source cite its own sources? | References, data tables, methodology described | No references, unsupported assertions |
| Peer review | Has it been checked by other experts? | Published in a peer-reviewed journal | Self-published blog, no editorial oversight |
Writing and speaking like a scientist
Scientific communication is not about sounding complicated — it is about being clear, precise and evidence-based. When you communicate a conclusion about waves or motion, follow these principles:
"If a source is scientific, it must be completely objective." No — all humans have perspectives. What matters is whether the source acknowledges limitations, cites evidence and has been subject to peer review. Objectivity is a process, not a guarantee.
"More evidence always makes a stronger argument." No — quality matters more than quantity. Ten weak sources do not outweigh one strong, peer-reviewed study with clear methodology.
Climate and wave research: Australian scientists at the Bureau of Meteorology and CSIRO use evidence from satellite data, buoy measurements and climate models to argue for changes in wave patterns around Australia's coast. Their arguments follow the CER framework: they make specific claims about changing swell patterns, present decades of measured data as evidence, and use physical oceanography reasoning to connect the data to climate drivers such as the Southern Annular Mode.
Road safety and Newton's laws: Transport for NSW uses evidence from crash investigations, computer simulations and international studies to argue for speed limits, seatbelt laws and road-design standards. Their reports explicitly evaluate source reliability, acknowledge limitations in data collection, and use Newton's laws to reason about force, mass and deceleration in collisions.
Aboriginal and Torres Strait Islander knowledge systems: Traditional ecological knowledge is increasingly recognised as a valid, reliable source of evidence in scientific arguments — provided it is documented ethically and with community consent. For example, observations of seismic and tidal patterns passed down through generations provide longitudinal evidence that complements instrument-based records.
1. In the claim-evidence-reasoning (CER) framework, what is the role of reasoning?
2. Which of the following is the strongest indicator that a scientific source is reliable?
3. A student wants to argue that wearing a bicycle helmet reduces head injury risk. Which piece of evidence would BEST support this claim?
4. A blog post claims that "microwave ovens are dangerous because they use nuclear radiation." Which evaluation is MOST accurate?
5. A student concludes: "Because F = ma, increasing the mass of a car always increases its acceleration." Which statement BEST evaluates this argument?
1. Explain the three parts of the claim-evidence-reasoning (CER) framework. For each part, give one example related to a waves or motion topic from this unit. 4 MARKS
2. You are researching whether mobile phone towers pose health risks. Describe two criteria you would use to evaluate the reliability of a source on this topic, and explain why each criterion matters. 4 MARKS
3. A newspaper headline reads: "Scientists Prove Heavier Objects Fall Faster!" The article cites a single experiment where a feather and a hammer were dropped in Earth's atmosphere. Construct a CER argument that evaluates this claim. In your reasoning, identify at least one limitation of the evidence presented. 4 MARKS
Go back to your Think First answer. Has your understanding changed?
C — Reasoning explains why the evidence supports the claim by using scientific principles to build a logical bridge between data and conclusion.
B — Peer review by qualified experts in a reputable journal is one of the strongest indicators of reliability. It means the methodology, data and conclusions have been independently scrutinised.
D — A large peer-reviewed study with controlled comparison of outcomes provides the strongest, most generalisable evidence. Personal stories, advertisements and informal polls are weak sources.
A — The claim confuses non-ionising electromagnetic radiation (microwaves) with nuclear (ionising) radiation. This is a scientific error that undermines the argument regardless of the blog's intent.
B — The student has misunderstood the inverse relationship in F = ma. For a constant net force, increasing mass decreases acceleration. The reasoning is flawed because it misapplies the mathematical relationship.
Model answer: The CER framework has three parts. Claim is a clear, testable statement answering the question — for example, "Sound travels faster through water than through air because water is denser." Evidence is reliable data supporting the claim — for example, measured values of 343 m/s in air and 1 480 m/s in water at 20 °C. Reasoning explains why the evidence supports the claim using scientific principles — for example, sound is a mechanical wave that propagates through particle collisions; water particles are closer together than air particles, so vibrations transfer more rapidly.
Model answer: Criterion 1 — Authority: I would check whether the authors are qualified experts in physics, epidemiology or telecommunications, and whether they are affiliated with a recognised research institution. This matters because expertise reduces the risk of factual errors. Criterion 2 — Peer review: I would check whether the source has been published in a peer-reviewed journal. This matters because independent expert review catches methodological flaws, biases and unsupported claims that a single author might miss.
Model answer: Claim: The headline's claim is misleading and not scientifically valid. Evidence: The experiment cited only compared a feather and a hammer in Earth's atmosphere, where air resistance acts strongly on the feather. Reasoning: In a vacuum, all objects fall at the same rate regardless of mass (Galileo's principle, demonstrated on the Moon). The observed difference in the experiment was caused by air resistance, not by mass itself. Limitation: The evidence lacks a control condition (vacuum) and generalises from a single, uncontrolled demonstration to all falling objects. A valid conclusion would require testing in a vacuum and controlling for air resistance.
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