Your teacher has two jars on the desk. Both hold the same mix of sand, salt and water. One of them is our baseline: poured through nothing, so we can compare every result against it later. How could we get the sand back out of the water, and how would we test a way fairly?
The theme is the same for everyone: separate the sand from the water. Your group chooses which two methods to compare:
- Sieving: pour the mixture through a sieve or colander to catch larger grains
- Filtering: pour through filter paper (or kitchen roll) in a funnel
- Settling: leave the mixture still, then gently pour off the clearer water
A strong testable question sounds like this: Does filtering leave less sand in the water than sieving?
Agree in your group which two methods you will compare and which you think will leave less sand, and why. You will write the full question on your Investigation Journal page in the next step.
Call out where each of the five cards belongs: Change, Measure, or Keep the same.
That sort is a fair test: change only one thing, measure one result, and keep everything else the same.
Then fill in the plan on your Investigation Journal page, with the same time rule for both methods (for example, two minutes to settle before you score). We all judge “sand left” on one cloudiness scale: 1 = clear, 5 = as cloudy as the baseline jar.
Plan our fair test
Collect only the tools for your group's two methods, then run the fair test you planned. After each trial, hold the result cup beside the baseline jar (the one poured through nothing) and score its cloudiness from 1 (clear) to 5 (as cloudy as the baseline), using the same rule every time.
Run each method twice (two trials each). Score cloudiness after every trial and write the score on your Investigation Journal page straight away. Keep the amount of mixture, the time rule and the container the same every time.
You’re doing what scientists do: same rules every time, so the numbers can be trusted.
Open your Investigation Journal page and check that every trial score is written down, because a score you only remember is a score you will have lost by the next lesson. Then keep the two kinds of writing apart: what you saw (the cloudiness score) goes in one place, and what you think it means goes in another, so that anyone reading your page can tell your evidence from your conclusion.
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