Plan a Fair Investigation
Change one factor, repeat your trials, and explain what the results support.
Lesson objectives
By the end of this lesson, you should be able to:
- Identify the independent variable, dependent variable, and controlled variables in a simple investigation.
- Plan a safe comparison that changes one factor while keeping other relevant conditions the same.
- Record repeated trials honestly and explain why results may vary.
- Use results to write a conclusion and describe the method clearly enough for others to repeat it.
A class needs a paper bridge to hold counters across a gap. Does folding the paper change how many counters it can hold?
Change one factor. Measure its effect.
These are the controlled variables. They help make the comparison fair.
Change the shape
Compare a flat sheet with an accordion-folded sheet.
Test each bridge
Add identical counters at the centre, one at a time, using the same method.
Measure the load
Count how many counters the bridge holds just before it falls.
Use fresh sheets for repeated trials. Keep all the results, compare the two shapes, and make a conclusion limited to what you tested.
The arrows show how the planned change leads to a measured result under shared conditions. They do not guarantee that the prediction will be supported.
1. Decide what changes and what stays the same
A variable is a factor that can vary. In a simple fair test, change one factor deliberately, measure the response, and keep other relevant conditions as similar as possible.
| Role | Scientific name | Paper bridge example |
|---|---|---|
| What you change | Independent variable | Paper shape: flat or accordion-folded |
| What you measure | Dependent variable | Number of counters held before the bridge falls |
| What you keep the same | Controlled variables | Paper type and size, gap width, counter type, and where counters are placed |
If the folded bridge also uses thicker paper, you cannot tell whether shape or thickness caused a difference. A controlled variable is a condition kept the same; it is not the same term as a control group.
2. Make a plan another group can follow
Hypothesis: Folding the paper may strengthen the bridge because the folds help it resist bending. Prediction: A folded sheet will hold more counters than a flat sheet under the same conditions.
- Work at a low table with an adult. Use two stable stacks of books with a 10 cm gap, six identical paper sheets, a ruler, and identical lightweight counters. Keep counters away from young children.
- Lay one flat sheet across the gap. Add counters one at a time at the centre until the bridge falls. Record how many it held just before falling.
- Repeat with two fresh flat sheets. Do not reuse damaged paper.
- Fold three fresh sheets into matching accordion shapes. Test each one using the same gap and loading method.
- Record all six results. Stop if the book stacks become unstable. Do not use heavy weights or stand on the bridge.
3. Let the evidence speak
The following numbers are made-up practice data, not promised results. Your bridge may behave differently.
| Shape | Trial 1 | Trial 2 | Trial 3 |
|---|---|---|---|
| Flat | 3 counters | 4 counters | 3 counters |
| Folded | 9 counters | 8 counters | 10 counters |
A careful conclusion is: “In these trials, the folded sheets held more counters than the flat sheets. This supports the prediction for our materials and method.” It does not show that every folded paper bridge is stronger in every situation.
4. Repeat, review, report
Repeated trials reveal variation and reduce the influence of a single unusual result. Similar results from another group can strengthen confidence. If results disagree with your idea, keep the records, check the method, and reconsider the explanation. Do not change data to make a prediction look correct.
Share your question, prediction, materials, procedure, results, conclusion, and any difficulties. Good instructions let others try the investigation. For a next question, investigate gap width while keeping bridge shape and other conditions fixed.
Review at a glance
The big ideas
- Change one factor deliberately and measure the response.
- Keep other relevant conditions the same so the comparison is fair.
- Repeat trials and record every result, including unexpected ones.
- Write a conclusion based on the results; explain the method so others can check it.
Key terms & meanings
- Investigation
- A planned way to answer a question by collecting and examining evidence.
- Experiment
- An investigation in which conditions are deliberately changed to test an idea.
- Variable
- A factor that can change or take different values.
- Independent variable
- The factor you deliberately change in a test.
- Dependent variable
- The outcome you observe or measure in response.
- Controlled variables
- Other relevant conditions that you keep the same.
- Fair test
- A comparison that changes the intended factor while keeping other relevant conditions alike.
- Procedure
- The steps used to carry out an investigation.
- Trial
- One run of a test; repeated trials help reveal variation.
- Data
- The observations and measurements recorded during an investigation.
- Conclusion
- An explanation of what the evidence suggests about the question.
- Bias
- An influence that can unfairly favour one result, such as recording only the results you like.
Change paper shape → count counters held → keep paper size, gap width, counter type, and loading position the same. Supporting a prediction is not proof that it is always true.
Study tip: Cover the meanings, explain each term in your own words, then check your explanation.