3
Making it fair
Workbook 2: Topic 3.4, pp. 38–40
GoalSay what to change, what to keep the same and what to measure in a fair test.
New words
fair test · a test where you change one thing and keep everything else the samechange · the one thing you test differently each timekeep the same · things that must not change, so the test is fair
Explanation
In a fair test we change only one thing. In the bridge test Mia changed the material. She kept these things the same: the size of the strips, the gap between the books and the coins. If she had used a long strip of card and a short strip of paper, the test would not be fair. We would not know if the material or the length made the difference. She measured the number of coins held. A fair test lets us trust the results. Doing the test again can check the results.
| Bridge test | |
|---|---|
| Change | the material |
| Keep the same | size of strip, gap, coins |
| Measure | number of coins held |
Worked examples
Leo tests a wide strip of card and a narrow strip of paper. This is not fair. Both strips should be the same size.
Amir puts the books close together for one bridge and far apart for another. That is not fair. The gap must be the same every time.
Before a test we predict: I think the card will be strongest because it is thicker.
Class activity
Spot the unfair test (with an adult): look at the bridge test from lesson 1. Make a list: what do we change, what do we keep the same, what do we measure? Now do the test with one thing changed on purpose, such as a longer strip. Does it still feel fair?
Practice
1
In a fair test, how many things do we change?
One.
2
Ana tests which paper makes the strongest bag. Fill in her plan.
| Ana’s bag test | |
|---|---|
| Change | ? |
| Keep the same | ? |
| Measure | ? |
Change: the kind of paper. Keep the same: the size of the bags and the coins she puts in. Measure: how many coins each bag holds before it tears.
3
Tom puts coins on the card bridge and big stones on the plastic bridge. Why is this unfair?
He used different loads. He must use the same coins on every bridge, so only the material changes.
4
What do we measure in the bridge test?
The number of coins the bridge holds.