Variables, Fair Tests and Drawing Conclusions — Answers
Answer sheet with model answers and success criteria for the Year 8 working scientifically worksheet.
Success TutoringWorksheetsAnswer sheetYear 8 · Science · Working ScientificallyVariables, Fair Tests and Drawing Conclusions — Answers
Part A: Name the variable
Circle the type of variable described.
A variable is anything that can change in an investigation.
The independent variable is the one you change on purpose. The dependent variable is the one you measure or observe, because it may depend on the change you made. Controlled variables are everything else that could affect the result, so you keep them the same.
A test is fair when only the independent variable changes. Then any difference in the dependent variable can be linked to that one change.
Scientists repeat each test (usually at least three trials) and calculate an average. Repeating makes results more reliable and helps you spot an outlier, a result that does not fit the pattern.
- Aindependent variable
- Bdependent variable
- Ccontrolled variable
Answer: independent variable
It is the variable Mia chooses to change.
- Aindependent variable
- Bdependent variable
- Ccontrolled variable
Answer: dependent variable
It is the variable she measures to see the effect of the change.
- Aindependent variable
- Bdependent variable
- Ccontrolled variable
Answer: controlled variable
It must be kept the same for every plant so it cannot affect the results.
- Aindependent variable
- Bdependent variable
- Ccontrolled variable
Answer: controlled variable
Leo should use the same ball every time so that only the drop height changes.
- Aindependent variable
- Bdependent variable
- Ccontrolled variable
Answer: dependent variable
Bounce height is what he measures.
- Aindependent variable
- Bdependent variable
- Ccontrolled variable
Answer: independent variable
Drop height is what he deliberately changes.
Part B: True or false?
Write T for true or F for false.
Answer: False
If two things change, you cannot tell which one caused any difference in the results. A fair test changes only one variable.
Answer: True
Repeats reduce the effect of small random errors and make outliers easier to spot.
Answer: True
Categories have no in-between values, so separate columns are used. When both variables are measured numbers, a line graph is used.
Part C: Analyse an investigation
Use the results below to answer the questions.
Investigation: Does the wing length of a paper helicopter affect how long it takes to fall to the floor?
Each helicopter was made from the same type of paper with one paperclip attached, and was dropped from a height of 2 m. The same student timed every drop with a stopwatch.
Results — time to fall (seconds)
Wing length 4 cm: trial 1 = 1.2, trial 2 = 1.4, trial 3 = 1.3, average = 1.3
Wing length 6 cm: trial 1 = 1.7, trial 2 = 1.6, trial 3 = 1.8, average = 1.7
Wing length 8 cm: trial 1 = 2.1, trial 2 = 2.3, trial 3 = 2.2, average = ?
Wing length 10 cm: trial 1 = 2.6, trial 2 = 2.5, trial 3 = 2.7, average = 2.6
Answer: The wing length of the paper helicopter.
Answer: The time taken for the helicopter to fall to the floor.
Answer: Any three of: the drop height (2 m), the type of paper, the number of paperclips (one), the same person timing, the same stopwatch, the wing width or shape, dropping in the same place (away from moving air).
Answer: 2.2 seconds
- 2.1 + 2.3 + 2.2 = 6.6
- 6.6 ÷ 3 = 2.2 s
Answer: 2.9 s is the outlier because it is much longer than the other two. Possible causes: the stopwatch was stopped late, the helicopter drifted sideways in moving air, or it caught on something as it fell. It should be repeated rather than included in the average.
Answer: A line graph, because both the wing length and the fall time are measured numbers (continuous data).
Answer: Model: If the wing length increases, then the helicopter will take longer to fall, because larger wings push against more air (more air resistance).
Part D: Conclusion
Model answer: As the wing length increased from 4 cm to 10 cm, the average time to fall increased from 1.3 s to 2.6 s. Every increase in wing length gave a longer average fall time, so helicopters with longer wings fall more slowly. This supports the hypothesis that longer wings make the helicopter take longer to fall. The pattern has only been shown for wing lengths between 4 cm and 10 cm.
Success criteria:
- Describes the trend (longer wings, longer fall time)
- Quotes data from the table, including units
- Links the result back to the hypothesis
- Does not claim more than the data shows
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.
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