Year 8 Science · Unit 4 · Lesson 14
Challenge Worksheet
Learning Goals
Find the mistake
A student's sugar-dissolving investigation has five data quality issues. For each issue, identify the problem, classify it (random error / systematic error / design flaw / insufficient data), and suggest an improvement.
| Issue | Classification | Suggested improvement |
|---|---|---|
| Only 2 trials were conducted at each temperature. | ||
| Temperature was measured with a kitchen thermometer rated ±5 °C precision. | ||
| The water was not stirred during dissolving — it was left to sit still. | ||
| Time was measured by watching a clock on the wall from across the room (parallax error). | ||
| The temperature range tested was only 20 °C to 30 °C (a 10 °C span). |
Design challenge
You have 30 minutes, one school laboratory, and basic equipment: ruler, stopwatch, spring scale, measuring cylinder, thermometer. Design an original mini investigation (not sugar dissolving) that meets all four criteria below.
(a) State a clear, testable research question. Identify the independent variable (IV) and explain why it can realistically be changed four times in 30 minutes.
(b) List your four IV values and explain why you chose this range. Then describe your data table structure (IV column, DV column, 3 trial columns, average column).
(c) Explain why your data would be suitable for a line graph (not a bar graph). What pattern or trend would you expect to see, and why?
(d) Identify one design limitation that could threaten the validity of your investigation and explain how you would minimise it.
Wrap Up
In one sentence, why does a well-designed investigation produce more trustworthy conclusions than a poorly designed one?