Science / Year 6 / Working Scientifically / 6.2
Estimated time: 40 minutes | Difficulty: Medium | Ref: KS2-WS-1a
Learning objective: Identify independent dependent and control variables
Use the pathway to build a clear mental model. Open each node and answer the check question.
A variable is anything that can change or vary in an investigation. In science, we need to identify and control variables to make our experiments fair. Think about an experiment - what things could be different each time you do it?
Check: Can you name three things that could vary in an experiment about plant growth?
The independent variable is the ONE thing you deliberately change in your experiment. You choose to vary it to see what effect it has. Remember: there should only be ONE independent variable in a fair test. Example: "I will change the amount of water I give the plant."
Check: In an experiment testing which surface a toy car rolls furthest on, what is the independent variable?
The dependent variable is what you measure or observe to see if it changes. It "depends" on what you changed. If you change the amount of water, you measure how tall the plant grows. The height DEPENDS on the water you gave it.
Check: In an experiment testing which material keeps water warmest, what would you measure?
Control variables are all the things you keep the same to make it a fair test. If you changed more than one thing, you wouldn't know which caused your results! For the plant experiment, you'd keep the same pot size, soil type, light level, and temperature.
Check: Why is it important to control these variables? What would happen if you didn't?
In science, a variable is anything that can change or be changed in an investigation. To carry out a fair test, you need to understand the three types of variables and how to use them correctly.
| Variable Type | What It Means | Memory Tip |
|---|---|---|
| Independent Variable | The ONE thing you deliberately change | "I" change the Independent variable |
| Dependent Variable | What you measure or observe (it DEPENDS on what you changed) | It "Depends" on the change |
| Control Variables | Everything you keep the same to make it fair | "Control" means keep Constant |
Question: "Does the size of a parachute affect how slowly it falls?"
Imagine you tested a large parachute made of plastic AND a small parachute made of paper. If the large one fell slower, was it because of the size or the material? You wouldn't know! By changing only ONE variable and keeping everything else the same, you can be sure what caused your results.
Understanding variables is essential for carrying out valid scientific investigations. Real scientists use the same principles - pharmaceutical companies testing new medicines must control every variable except the one they're testing. Without proper variable control, we couldn't trust any scientific conclusions!
Question: Which brand of paper towel absorbs the most water?
Question: How does the type of exercise affect your heart rate?
Question: Does water temperature affect how quickly sugar dissolves?
Question: Which surface creates the most friction for a toy car?
Answer all questions, then check your answers. Your quiz result is saved on this device.
✗ Wrong: "The dependent variable is what I change."
✓ Right: "The independent variable is what I change. The dependent variable is what I measure - it depends on what I changed."
Remember: "I" change the Independent. The Dependent "D"epends on my change.
✗ Wrong: "I'll test a big blue balloon and a small red balloon to see which floats longest."
✓ Right: "I'll test balloons of different sizes, but they'll all be the same colour, material, and filled with the same amount of helium."
If you change two things (size AND colour), you won't know which caused your results!
✗ Wrong: "I'll keep the same cup" (but forgetting about temperature, amount of water, etc.)
✓ Right: "I'll keep these the same: cup type, water amount (200ml), water temperature (20°C), stirring speed, timing method."
Think carefully about EVERYTHING that could affect your results. List all your control variables!
✗ Wrong: "I measured how it did."
✓ Right: "I measured the time in seconds for the ice cube to melt completely."
Be specific! Say exactly what you changed, what you measured, and include units where possible.