In a paper-spinner investigation, changing paper-wing length is the independent variable; descent time over a fixed height is the dependent variable. The same paper type, folding method and release height are controlled variables. A factor is not independent just because it is important: its role depends on what the method deliberately changes.
If wing length and paper thickness change together, a time difference cannot be assigned to wing length alone. Control relevant alternatives, record unavoidable variation and specify the ranges. “Keep everything the same” is not a usable instruction unless the important conditions are named and implemented.
Book notes: Name variables in the actual method
In a paper-spinner investigation, changing paper-wing length is the independent variable; descent time over a fixed height is the dependent variable. The same paper type, folding method and release height are controlled variables. A factor is not independent just because it is important: its role depends on what the method deliberately changes.
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When wing length is deliberately varied, wing length is the:
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Link the prediction to a measurable response
Link the prediction to a measurable response
A hypothesis connects the independent and dependent variables and predicts an observable result: “Increasing spinner wing length from 3 cm to 6 cm will increase mean descent time from a fixed 1.5 m release height under still indoor air.” The prediction could be contradicted by evidence.
A question asks what relationship will be investigated; a hypothesis proposes a relationship to test. Do not require the hypothesis to be correct. Its value is that it makes the expected pattern explicit and allows the data to challenge it. Include a possible scientific rationale, while keeping it distinct from the observation.
Book notes: Link the prediction to a measurable response
A hypothesis connects the independent and dependent variables and predicts an observable result: “Increasing spinner wing length from 3 cm to 6 cm will increase mean descent time from a fixed 1.5 m release height under still indoor air.” The prediction could be contradicted by evidence.
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Which is the dependent variable in a temperature–dissolving-time test?
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A control group is not a controlled variable
A control group is not a controlled variable
A baseline or control group provides a reference comparison, such as untreated plants alongside a treatment. Controlled variables are conditions maintained across groups, such as plant age and water supply. An experiment can have controlled variables without an untreated group, and a control group alone does not fix poor control of other conditions.
Random assignment or randomised trial order can reduce some biases. Repetition estimates variation; it does not repair a confounded design. A clear variable table should state how each factor changes, is measured or is kept consistent, so readers can evaluate whether the comparison addresses the question.
Book notes: A control group is not a controlled variable
A baseline or control group provides a reference comparison, such as untreated plants alongside a treatment. Controlled variables are conditions maintained across groups, such as plant age and water supply. An experiment can have controlled variables without an untreated group, and a control group alone does not fix poor control of other conditions.
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Why keep sugar mass consistent?
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Worked example
Worked example: Test whether water temperature affects the dissolving time of equal sugar portions. Define the variables.
Independent: initial water temperature, for example 15, 25 and 35 °C under teacher-approved handling.
Dependent: time until no visible crystals remain under a defined observation rule.
Controls: water volume, sugar mass and crystal size, container, stirring method.
Hypothesis: higher initial temperature will reduce mean dissolving time under these conditions.
The method changes one specified factor and measures a defined response while controlling plausible alternative influences.
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Activities
Activities
Activity 1
A student changes sugar mass and water temperature together. Diagnose the design problem and repair it.
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Activity 2
Write a variable table for paper-spinner wing length and descent time, including three controls.
Five questions from this lesson’s eight-question bank
Answer the five-question Quick Check. Use the feedback to repair an idea before retrying.
Short answer
Explain and evaluate
Q1. Identify IV, DV and three controls for a spinner investigation.
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Explain and evaluate
Q2. Explain why ten repeats do not repair changing sugar mass and temperature together.
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Explain and evaluate
Q3. Write a question and a hypothesis for a safe paper-spinner investigation.
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Answers and model responses
Activities
Activity 1
The factors are confounded. Keep sugar mass and other relevant conditions fixed while changing temperature, or use a clearly designed factorial investigation if appropriate.
Activity 2
IV wing length in cm; DV descent time in s over fixed distance; controls paper type, folding/attachment method, release height/technique and air conditions, each with an implementation rule.
Short Answer Model Answers
Q1: IV wing length; DV descent time over fixed height; controls include paper type, folding/attachment, release technique/height and air conditions. State how each is implemented.
Q2: Both factors still vary together, so either can explain the response. Repeats estimate variability in the confounded comparison but do not isolate temperature.
Q3: Question: how does wing length affect mean descent time over a fixed height? Hypothesis: increasing wing length across a stated range will increase mean descent time under fixed conditions. Accept another measurable directional prediction with suitable conditions.
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Revisit and reflect
Revisit without looking
Identify independent, dependent and controlled variables.
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Check the key idea
The method changes one specified factor and measures a defined response while controlling plausible alternative influences.