Lesson focus: A planA description of what you will do in an investigation and why. makes the evidenceObservations or measurements used to show whether an idea is right or wrong. trustworthy before the first measurement is taken.
Plan an investigation with apparatus, sequence, variables, repeatDoing the same measurement again in the same way, to check how close the results are. and safety control measures.
Build on earlier learning
Scientific investigations: independent, dependent and control variablesRevisit independent, dependent and control variables before turning them into a complete plan.
Planning an investigation?
Design an investigation with CORMMSSA step-by-step Logic Lab guide to planning a fair test, with a worked example and practice.
You will be successful when you can…
- Write a method another person could follow.
- Choose a safe range and suitable intervals.
- Plan repeats and a raw-data table.
- Link safety control measures and control variables to specific risks.
Words that carry the science
- plan
- A justified design for collecting evidence.
- repeat
- A new measurement made under the same stated conditions.
- interval
- The step between consecutive independent-variable values.
- pilot study
- A small trial used to improve the main method.
- endpoint
- The defined event at which a measurement stops.
Design the evidence before collecting it
01Specify apparatus and sequence
List apparatus with sizes or resolutionThe smallest change a measuring instrument can show, such as 1 mm on a ruler. where this affects evidence. Write numbered steps using measurable quantities rather than “some” or “a while”.
Define the endpointThe clear sign you agree in advance that tells you when to stop the timer or the test, such as a cross disappearing from view. before collecting data—for example, “stop timing when no solid crystals are visible after 5 seconds without stirring”.
02Choose range, intervals and repeats
A safe rangeThe spread from the lowest to the highest value, such as the values an instrument can measure or the values in your results. tests enough values to reveal a pattern. Testing only the two ends cannot show whether the change in between is steady or curved. Suitable intervalThe gap between the values you choose for your independent variable, such as testing every 10 °C. give useful detail without pretending the apparatus can control values exactly.
repeatDoing the same measurement again in the same way, to check how close the results are. under the same conditions reveal variation and support a mean. They do not fix a biased measuring method. A pilot studyA small practice run done before the main investigation to check the method works. can reveal whether the range and endpointThe clear sign you agree in advance that tells you when to stop the timer or the test, such as a cross disappearing from view. work.
03Prepare the table and control variables
A blank results table forces the planA description of what you will do in an investigation and why. to name variables and units before practical work starts. Include separate columns for raw repeats and calculated values.
Distinguish safety control measures, which reduce harm, from control variables, which keep the comparison fair. Some actions can support both.
Start with the evidence needed, then design how to obtain it.
- ClaimWhat question should the conclusion answer?
- EvidenceWhat outcome and pattern would address it?
- MeasurementsWhich values, units, range and repeats are needed?
- MethodWhat exact sequence keeps comparisons valid?
- ControlsHow will risk and important variation be reduced?
Plan for surface area
Investigate how tablet surface area affects dissolving time.
- Use equal-mass tablets from the same product: whole, halves and crushed samples.
- Measure equal water volumes at the same temperature in identical containers.
- Add the sample, start timing consistently and use a defined endpoint.
- Repeat each condition, record raw times and calculate a mean.
How to make the reasoning visible: Surface area must change without changing mass, water conditions or the definition of “dissolved”.
Evidence-ready plan
Use this planning frame before writing the final numbered method.
| Decision | Planned choice | Reason |
|---|---|---|
| Independent variable | Whole, halved and crushed equal-mass tablet | Changes exposed surface area |
| Dependent variable | Time to defined endpoint / s | Quantifies dissolving rate indirectly |
| Controls | 100 mL water at 25 °C; same container; no stirring | Reduces alternative explanations |
| Repeats | Three fresh trials per condition | Shows variation and supports a mean |
| Safety | Eye protection; avoid inhaling powder; clean spills | Reduces splash, dust and slip risks |
Why must you use fresh water and a new tablet for each repeat?
Write the column headings for a results table for this investigation.
Look at the safety row in the table. Name one hazard in this investigation and the control measure that reduces it.
Check your understanding
Answer from memory, then check against the suggested answer.
What is a pilot study?
Why draw your results table before you start?
What do repeats show?
What is an endpoint?
What is an interval?
A student tests only 10 °C and 80 °C. Why should they add temperatures in between?
Which is better: testing five temperatures three times each, or two temperatures ten times each? Explain.
Why should the endpoint be decided before the investigation starts?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Plan an investigation into how water temperature affects the time taken for sugar to dissolve. Answer each step of the plan.
What will you change, and how will you keep the water fair? Name the temperatures and the volume of water.
(1)What should be the same about the sugar each time?
(1)Name one other thing you will keep the same.
(1)How will you make your results more trustworthy?
(1)How will you record your results?
(1)Give one safety step.
(1)Total for this question: 6 marks
Command word: For planA description of what you will do in an investigation and why., write steps that someone else could follow, and say how each step makes the results fair or safe.