Planning a fair test: variables and method
A well-planned investigation answers its question the first time. Almost all of that planning is deciding what to change, what to measure and what to keep the same.
Part of your national curriculum
- Working scientifically: Select, plan and carry out the most appropriate types of scientific enquiry to test predictions, including identifying independent, dependent and control variables
Lesson overview
What you'll learn in this lesson
Select, plan and carry out the most appropriate types of scientific enquiry to test predictions, including identifying independent, dependent and control variables
Key learning points
- • The three types of variable
- • Choosing the type of enquiry
- • Writing a testable prediction
- • Range, interval and safety
This lesson at a glance
- 28 minutes
- 21 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 21
Visual introductionPicture this
Planning a fair test: variables and method
A well-planned investigation answers its question the first time. Almost all of that planning is deciding what to change, what to measure and what to keep the same.
In a nutshell
Select, plan and carry out the most appropriate types of scientific enquiry to test predictions, including identifying independent, dependent and control variables
Learning cycle
Part 2 of 21
Learning cycle 1 of 2
Part 1 · The three types of variable
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 21
Learn
The three types of variable
The independent variable is what you deliberately change, the dependent variable is what you measure, and control variables are everything you keep the same so the results are a fair test. Naming all three, with units, is the first thing an examiner looks for in a plan.
Reset break
Part 4 of 21
Pause
That's sitting 1 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 21
Learn
Choosing the type of enquiry
Not every question suits a fair test. Some are answered by careful observation over time, some by identifying and classifying, some by looking for patterns in large data sets, and some by research using secondary sources. Choosing the wrong type wastes the investigation.
Quick check
Part 6 of 21
Quick check
Part 7 of 21
Reset break
Part 8 of 21
Pause
That's sitting 2 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 21
Learning cycle 2 of 2
Part 2 · Writing a testable prediction
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 21
Learn
Writing a testable prediction
A prediction should state the direction of the expected effect and give a scientific reason: 'as temperature increases the rate of reaction will increase, because particles move faster and collide more often'. A prediction without a reason is a guess and earns little credit.
Explore the idea
Part 11 of 21
Learn
Range, interval and safety
Choose a range wide enough to reveal a pattern and enough intervals within it, usually at least five, to plot a meaningful graph. Identify hazards, state the risk and give a specific control measure: 'hot water can scald, so use a heatproof mat and carry beakers with a cloth'.
Reset break
Part 12 of 21
Pause
That's sitting 3 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 13 of 21
Quick check
Part 14 of 21
Explore the idea
Part 15 of 21
Worked example
Worked answer: plan an investigation into how temperature affects the rate of a reaction (4 marks)
The independent variable is the water bath temperature, tested at 20, 30, 40, 50 and 60 °C (1). The dependent variable is the time taken for the cross under the flask to disappear, measured in seconds with a stopwatch (1). Control variables include the volume and concentration of each solution, the same flask and the same observer judging the endpoint (1). Each temperature is repeated three times and the mean calculated, with anomalies excluded, to improve reliability (1).
Reset break
Part 16 of 21
Pause
That's sitting 4 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 17 of 21
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 18 of 21
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Some are answered by careful observation over time, some by ____ and classifying, some by looking for patterns in large data sets, and some by research using secondary sources.
A prediction should state the direction of the expected effect and give a ____ reason: 'as temperature increases the rate of reaction will increase, because particles move faster and collide more often'.
Challenge round
Part 19 of 21
Game · Recall cards
Dark beetles rise from 18% to 67%. What can be concluded directly?
Card 1 of 4
Mastery quiz
Part 20 of 21
Marked quiz
End of lesson quiz: Planning a fair test: variables and method
4 questions, marked with the reasoning shown. No timer.
1. Dark beetles rise from 18% to 67%. What can be concluded directly?
2. What makes the model-beetle test fair?
3. Which conclusion is strongest?
4. What is the independent variable?
Lesson round-up
Part 21 of 21
Lesson round-up
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Select, plan and carry out the most appropriate types of scientific enquiry to test predictions, including identifying independent, dependent and control variables