Year 7 Science · Unit 2 · Lesson 19
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Learning Goals
Compare two
Complete the table to compare a valid investigation and a reliable investigation. Use your lesson notes to fill in both cells for each feature.
| Feature | Valid investigation | Reliable investigation |
|---|---|---|
| What does it mean? | ||
| Key requirement | ||
| How you improve it | ||
| Type of error it reduces | ||
| Can you have one without the other? |
Order the steps
Number the steps from 1 to 7 to show the correct order for designing a fair test investigating how temperature affects the rate at which sugar dissolves. Step 1 = what you do first.
| Order | Step |
|---|---|
| Draw a blank results table with columns for temperature (IV), and three trial times plus an average (DV). | |
| Write a step-by-step method that anyone could follow, including the mass of sugar and volume of water to use each time. | |
| Write a research question: "Does water temperature affect how quickly sugar dissolves?" | |
| Identify the IV (water temperature), DV (time for sugar to dissolve) and at least three controlled variables (e.g. mass of sugar, volume of water, stirring rate). | |
| Write a hypothesis using "If… then… because…" — e.g. "If the water temperature increases, then the sugar will dissolve faster, because higher temperature gives particles more energy to collide." | |
| Carry out the experiment three times at each temperature and record results in the table. | |
| Calculate the average dissolving time for each temperature and analyse whether the results support the hypothesis. |
1. A student tests whether salt type affects dissolving rate but accidentally uses different volumes of water each time. Which quality of their experiment is reduced — reliability or validity? Explain why.
2. A student's results for the same temperature are: 45 s, 43 s, 44 s. Another student's results are: 30 s, 55 s, 41 s. Which student's results are more reliable? How do you know?
Wrap Up
In one sentence, what was the main idea of this lesson?