ACARA v9 CONTENT DESCRIPTION “develop investigable questions, reasoned predictions and hypotheses to explore scientific models, identify patterns and test relationships”
Builds on earlier work observing and wondering about the world. Here a vague wondering becomes a sharp, investigable question: one that names a single thing to change and a clear thing to measure, so that an experiment can give a real answer.
From a wondering to a testable question
Not every question can be answered by an experiment. Questions about what is prettier or what people ought to do are opinions. A scientific question must point to something you can change and something you can measure. The trick is to pick just one thing to change, called the independent variable, so that any change in the result can be traced back to it.
Frame the question: pick the one thing to change
An egg sinks in fresh water but can float in salty water. To turn this into a testable question, choose the single variable you will change.
You notice an egg floats in very salty water but sinks in tap water. You want to ask a question science can test about how much salt it takes.
Variable being tested: The amount of salt dissolved in the water (this one we change)
Which one variable you change on purpose
Not a fair test yet: more than one thing is changing, so you could not tell which change caused the result. Hold every other variable the same.
Predict with a reason
A prediction is more than a guess. A reasoned prediction says what you expect and why, using a science idea you already know. Salty water is denser than fresh water, and denser liquid pushes up on an object more strongly. So a reasoned prediction is: as more salt dissolves, the egg will float higher. The experiment then tests whether that relationship really holds.
Now name what you will measure
A testable question also needs a clear result to record. Lock in what counts as the answer before you start.
To answer how salt affects floating, you must record the same measurement every time you add more salt.
Variable being tested: The amount of salt dissolved in the water (this one we change)
The height the egg floats, measured in centimetres each trial
Not a fair test yet: more than one thing is changing, so you could not tell which change caused the result. Hold every other variable the same.
Look for the relationship in the results
Once the question is sharp and the measurement is chosen, you run trials and look for a pattern. Suppose you add salt one spoon at a time and measure the floating height. A clear relationship would have the height climb steadily as the salt increases. As you read the trial data, watch for any single result that does not fit the rising trend, because that is the one worth checking before you trust the pattern.
Test the relationship: find the reading to recheck
An egg was floated in water with more and more salt. The floating height in millimetres was measured at each amount. One trial does not fit the steady climb.
Click the point that does not fit the pattern of the others.
Does the evidence back the prediction?
A reasoned prediction is only worth keeping if the evidence supports it. The prediction was that more dissolved salt makes the water denser, so the egg floats higher. Sort each finding by whether it actually supports that idea, or whether it is beside the point. Good questioning means telling real evidence apart from facts that sound related but do not test the claim.
Weigh the evidence for the prediction
The prediction: more dissolved salt makes water denser, so the egg floats higher. Decide which findings are evidence for it.
Claim: Adding more salt makes the egg float higher because the water becomes denser.
When 40 g of salt was dissolved, the egg floated higher than with 10 g.
Measured with a balance, 1 litre of the saltiest water weighed more than 1 litre of tap water.
The glass holding the salty water was a pleasant shade of blue.
In plain tap water with no salt added, the egg sank to the bottom.
The experiment was carried out on a Tuesday afternoon.
Decide whether each statement is evidence for the claim, or not.
Why this matters
Every investigation begins with a question that can actually be answered. Learning to spot the one variable to change, to name what you will measure, and to predict with a reason turns idle curiosity into real science. It is the same first step a chemist, a doctor or an engineer takes before any experiment.
Quick self-check
1. Which question can science actually test by experiment?
2. In a testable question, the one thing you deliberately change is called the...
3. A good investigable question changes...
4. A reasoned prediction for the salt and egg test would be:
5. Why must you decide what to measure before you start?