ACARA v9 CONTENT DESCRIPTION “plan and conduct valid, reproducible investigations to answer questions and test hypotheses, including identifying and controlling for possible sources of error and, as appropriate, developing and following risk assessments, considering ethical issues, and addressing key considerations regarding heritage sites and artefacts on Country/Place”
Builds on the fair test and the reproducible plan. A Year 9 investigation adds two demands that pull in different directions: it must be valid, measuring the thing you actually intend with confounds controlled, and reproducible, written so another group repeats it and gets consistent results. Along the way you identify and control sources of error, follow a risk assessment, and work ethically and respectfully on Country and Place.
The scenario: heat lost to the wind
A class investigates how much heat a small camp fire loses to moving air. At a managed firepit they heat a fixed volume of water in a metal billy and record how fast its temperature rises, first in still conditions and then with a steady breeze from a fan. The question is whether wind lowers the heating rate, and by roughly how much.
Validity: measuring what you mean to measure
A valid investigation measures the intended thing and nothing else. Here the intended effect is the wind, so everything that could also change the heating rate must be held steady: the same volume of water, the same starting temperature, the same fuel load and arrangement, the same billy and lid, the same distance from the flame. If the fuel load or the starting temperature drifts between trials, a slower rise could be blamed on wind when the real cause was a smaller fire or warmer starting water. Controlling these confounds is what makes the comparison fair, and therefore valid.
Control the confounds so the wind test is valid
You are testing whether wind lowers the heating rate. Wind is the one thing you change. Decide what to do with every other variable so the comparison stays valid.
At a managed firepit your class heats a fixed volume of water in a billy, once in still air and once with a steady breeze from a fan, and times the temperature rise.
Variable being tested: Wind across the fire (still air versus a steady fan breeze) (this one we change)
The volume of water and its starting temperature
The fuel load, its arrangement and how the fire is lit
The billy, the lid and the distance from the flame
The thermometer, where it sits and the timing of each reading
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.
Reproducibility: writing it so others get consistent results
Validity makes one comparison trustworthy; reproducibility makes the whole method shareable. To be reproducible the plan must pin down the quantities and timing: exactly how much water, the fan speed and its distance, the reading interval, and how many repeat trials to average. A method that says heat some water with a fan blowing is too vague to repeat, and the next group would get scattered numbers. A method that fixes every quantity and rule lets another class follow the same steps and reach consistent results.
Identifying and controlling sources of error
Even a valid plan carries error, and a good scientist names it rather than hiding it. Thermometer reading varies between people, so you fix one reading rule and ideally one reader. Gusts come and go, so you hold the fan steady and discard a trial spoiled by a stray wind change. Single trials can mislead, so you repeat and average. Each of these is a source of error you identify and then control, so scatter from the method does not drown the real effect of the wind.
Choose how many trials to run at each wind setting
Each choice carries a benefit and a cost for how reliable and reproducible the result is. Pick one to see the trade-off.
Your group must decide how many timed runs to do in still air and in the breeze. The choice affects both the time on the day and how trustworthy the averaged result is.
Choose a response to see what is gained and what is given up.
The risk assessment
Working with flame and hot water means a risk assessment is part of the plan, not a formality. You list each hazard and the control beside it: open flame, so a bucket of water and a lid stay within reach and the fire is never left unattended; hot metal, so the billy is lifted with gloves and a cloth; bushfire risk, so no fire is lit on a total fire ban day and the site is cleared of dry leaf litter. Writing the controls down is also what lets the next group repeat the work safely, which ties risk management back to reproducibility.
Ethics and heritage on Country and Place
Choosing where to set up the firepit means recognising that the land is Country and Place. Some sites, rocks and artefacts hold cultural heritage significance for Aboriginal and Torres Strait Islander peoples. Grinding grooves, arrangements of stones, scarred trees and marked rocks can be culturally and legally protected. The ethical and lawful plan is to leave any such site, rock or artefact undisturbed, never remove or damage it, and seek permission and guidance from Traditional Owners before working in an area.
Sorting the plan: valid, reproducible, safe and respectful
Before lighting anything, check each planned action against the claim that this is a well-designed investigation: one that is valid, reproducible, safe, and respectful of heritage on Country and Place. Sort each action by whether it genuinely supports that claim or whether it does not belong in the plan at all.
Judge the plan for the wind-and-fire investigation
The claim: this plan is valid, reproducible, safe and heritage-respecting. Decide which actions support it.
Claim: This plan is a valid, reproducible, safe and heritage-respecting investigation of how wind affects the heating rate of a fire.
Hold the water volume, fuel load and thermometer position identical so only the wind changes between trials.
Run three timed trials at each wind setting and average them, with one fixed rule for reading the thermometer.
If a grooved rock or arrangement of stones is found at the site, leave it undisturbed and seek guidance from Traditional Owners before going further.
Change the fuel load and starting water temperature between trials to make the runs more interesting.
Light the fire on a total fire ban day and leave the flame unattended to save time.
Decide whether each statement is evidence for the claim, or not.
Why this matters
A result others can trust has to be both valid and reproducible: it measures the right thing, with confounds and sources of error controlled, and it is written so anyone can repeat it and get consistent numbers. For real investigations that also means a worked risk assessment and acting ethically and respectfully on Country and Place. Engineers, environmental scientists and heritage officers plan exactly this way, so that the evidence is reliable and the land and its cultural heritage are protected.
Quick self-check
1. You measure how much heat a small wood fire loses to wind by recording water temperature in a billy. What makes the investigation valid?
2. A reproducible energy investigation is one where...
3. Your thermometer is read by a different person each trial and the numbers jump around. This is best described as a...
4. Which belongs in the risk assessment for an outdoor heating investigation?
5. While choosing a field site you find a rock with old grinding grooves and an arrangement of stones. The right action is to...