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S2.1 Exploring and designing

Syllabus
First assessment 2025
Topic
S2.1
Level
SL

Form Research Questions

Start with evidence, then narrow the question

Consult varied sources, select information that is relevant and sufficient, and note the conditions under which each claim applies. Use that background to identify a measurable relationship or comparison—not merely a broad topic.

Stage What it must contain Pendulum example
Research question System, independent variable, dependent variable and conditions How does pendulum length affect period when the release angle is kept small?
Hypothesis A testable relationship supported by physics Period increases with length, consistent with the pendulum model
Prediction The observable outcome expected from the planned measurements Longer pendulums will take longer per oscillation

Explain the prediction

Connect the expected change to scientific understanding and state the assumptions that make the model useful. Independent thinking means using sources to justify and refine the question, not copying a source's conclusion.

Keep the three stages distinct

A question asks what will be investigated; a hypothesis proposes a relationship; a prediction states what the measurements should show. Each must remain testable by the proposed evidence.

S2.1.1 Exam Analysis

Assessment in practice

2 marks
How it is assessed

Questions identify two reasons why a scientific model is useful.

Command terms

Identify

What earns marks

Give two distinct functions, such as prediction, explanation, visualization or simplification.

Watch for

Repeating one benefit in different words or giving a feature of a model rather than its scientific use.

Design an Investigation

Design backwards from the evidence needed

Choose whether a hands-on experiment, database, simulation or model can answer the research question. Then specify how the independent variable will be changed, the dependent variable measured and relevant control variables held constant.

Design choice What to justify
Independent-variable range Wide enough to reveal the expected relationship, safe and within apparatus/model limits
Number and spacing of values Sufficient to show a trend or shape without clustering all evidence in one region
Repeats Enough to reveal random variation and support a representative value
Measurement method Apparatus, resolution, sequence, timing, geometry and how each value is obtained
Control variables Why each could affect the dependent variable and how it will be kept constant

Pilot before fixing the method

A short pilot checks whether the range produces measurable changes, whether the apparatus resolution is adequate and whether the sequence is practical. Use its observations to revise the method; do not invent or discard results to fit the hypothesis.

A valid method changes one intended cause at a time

Give enough procedural detail for another student to reproduce the investigation. A larger range, more readings or different technology is an improvement only when it strengthens the evidence for the stated relationship.

S2.1.2 Exam Analysis

Assessment in practice

1 marks
How it is assessed

Questions identify a control variable or suggest widening a star-temperature range.

Command terms

State / Suggest

What earns marks

Name a measurable variable to keep constant, or state that a wider range improves the test of the relationship.

Watch for

Naming an uncontrolled or irrelevant quantity, or proposing more precision without improving the range.

Control Experimental Variables

Control an effect because it could change the outcome

For every control, state the unwanted influence, the practical action and how that action protects the dependent measurement. A variable name alone does not show that the investigation is controlled.

Unwanted influence Practical control Why it helps
Instrument offset or sensor drift Zero and calibrate before use; record any correction Prevents a fixed offset from being mistaken for a physical effect
Changing environmental conditions Monitor and maintain the relevant condition Stops an external change from becoming a second independent variable
Heat exchange Insulate against heat loss or gain where relevant Keeps energy transfer outside the intended system small
Friction or unwanted electrical resistance Reduce it consistently or account for it in the design Limits unintended energy loss or voltage change
Background radiation Measure the background under the same conditions and correct the signal Separates source counts from background counts

Example — pendulum timing

If length is the independent variable and period is measured, keep a measurable release condition such as the initial angle constant; bob mass, diameter or material may also matter to the chosen setup. Explain how the same value is reproduced for every trial.

Control the system, not merely the equipment name

Saying “use the same stopwatch” or “keep gravity constant” does not identify a controllable influence in this design. Name a measurable feature and the method used to maintain it.

S2.1.3 Exam Analysis

Assessment in practice

1 marks
How it is assessed

Questions ask for one variable that needs to be controlled in a materials experiment.

Command terms

State

What earns marks

Name a relevant measurable property such as material, dimensions, mass or applied rate, not an unrelated environmental condition.

Watch for

Giving an irrelevant variable such as atmospheric pressure when the method’s material and geometry are the actual controls.

Retrieve Investigation Design

Design from a question

Turn context into a measurable question, hypothesis and prediction with independent, dependent and controlled variables.

Make evidence reliable

Choose a useful range and repeats, calibrate instruments, control relevant conditions and reduce or correct known losses and background.