ACARA v9 CONTENT DESCRIPTION “use provided scaffolds to plan and conduct investigations to answer questions or test predictions, including identifying the elements of fair tests, and considering the safe use of materials and equipment”
Builds on earlier work where you watched and wondered about the world. Now you learn to plan a test that gives a fair answer: change just one thing, keep everything else the same, and use your equipment safely.
What makes a test fair?
Imagine you want to know which surface melts an ice cube fastest, a metal tray or a wooden board. To be fair, the ice cubes must be the same size, sit in the same warm room, and start at the same time. The only thing you change is the surface. Then if one cube melts faster, you can be sure the surface caused it, not something else.
Plan the ice test: change one thing, keep the rest the same
You are testing whether a metal tray or a wooden board melts an ice cube faster. Choose the one thing you will change, and keep everything else fair.
Two ice cubes, two surfaces. You want to find out which surface melts ice faster, so you must keep everything fair except the surface itself.
Variable being tested: The surface the ice sits on (metal or wood) (this one we change)
The size of each ice cube (use the same size)
The room they sit in (use the same warm room)
The time you start the clock (start them together)
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.
Doing a step the safe way
Planning a test also means thinking about safety. Some steps can be done in more than one way, and the safer way protects your hands, your eyes and the people around you. To melt ice quickly you might warm the room or use warm water nearby. Warm water from the tap is much safer than boiling water, and an adult should handle anything hot.
Pick the safer way to warm the ice
You want the ice to melt a bit faster so the test does not take all day. Choose how to add warmth, and see what each choice gives and gives up.
To melt the ice cubes a little faster, you need some warmth near them. There is more than one way to do this, and some ways are safer than others.
Choose a response to see what is gained and what is given up.
Which actions make the test fair and safe?
A good plan has actions that keep the test fair and actions that keep you safe. Some things you might do, though, have nothing to do with either. Now think about a different question, whether more sun grows taller bean plants, and sort which actions really make that test fair and safe.
Sort the actions for the bean plant test
The plan: grow bean plants to see if more sun makes them taller. Decide which actions help make the test fair and safe, and which do not.
Claim: To test if more sun grows taller bean plants, I should plan a fair test and use equipment safely.
Give every plant the same amount of water each day.
Use the same size pot and the same soil for every plant.
Wash your hands after touching the soil.
Paint the pots your favourite colour before you start.
Measure each plant with a ruler in centimetres so you can compare fairly.
Decide whether each statement is evidence for the claim, or not.
Why this matters
Planning a fair test is the first job a scientist does. When you change just one thing, keep the rest the same, measure carefully and stay safe, your answer can be trusted. The same careful planning is used by gardeners, cooks and engineers every day.
Quick self-check
1. In a fair test of which cup keeps water warm longest, what should you change?
2. You are testing if more sun grows taller bean plants. To be fair, you should keep the same...
3. The one thing you change on purpose in a fair test is called the...
4. Why should you measure with a ruler instead of guessing by eye?
5. When testing which surface melts ice fastest using hot water nearby, the safe thing to do is...