Year 8 Science · Unit 4 · Lesson 12
Apply Worksheet
Learning Goals
Compare two
Complete the table to compare a reliable investigation with a valid investigation. Some cells have been started for you.
| Feature | Reliable Investigation | Valid Investigation |
|---|---|---|
| What it ensures | Results are consistent when the experiment is repeated | |
| What threatens it | Uncontrolled variables; wrong measuring tool; systematic error | |
| How to improve it |
Find the flaw
Investigation with problems
A student investigates whether background music affects plant growth. They place five plant pots near a speaker playing pop music continuously and measure their height at the end of four weeks. No control group was used. Each plant pot was in a different room of the house with varying amounts of natural light. Only final height was recorded. No details about the music volume or type were noted.
For each problem below, classify it (validity / reliability / sample size) and suggest a specific improvement.
| Problem | Classification (V / R / SS) | Specific improvement |
|---|---|---|
| Only 1 plant per condition (music vs no music) | ||
| No control group (plants with no music) | ||
| Plants in different rooms with different light levels | ||
| Height measured only once at the end, not tracked over time | ||
| No description of music type or volume recorded |
1. A scientist gets the same result three times in a row. Does this mean the data is valid? Explain why or why not using an example.
2. Why does having a control group improve the validity of an investigation? What would happen if all science experiments had no control group?
Wrap Up
In one sentence, what was the main idea of this lesson?