A fair test is an experiment where you change only one thing and keep everything else the same. Then, if the result changes, you know which thing caused it. The thing you change is the variable you test; the thing you measure is your result.
Suppose you want to know whether the height of a ramp affects how far a toy car rolls. Change only the ramp height. Keep the same car, the same floor and let go the same way each time, without pushing. Measure how far the car rolls each time. If you changed two things at once, you could not tell which one made the difference.
Worked example
Sam tests which paper towel soaks up most water, but uses different amounts of water for each. Is it fair?
- A fair test changes only the towel.
- The amount of water must stay the same.
Answer:No, it is not fair: he should use the same amount each time.
Key words
- fair test
- only one thing is changed
- variable
- something that can change in an experiment
- measure
- find out the result with a tool
- keep the same
- do not change, so the test is fair
New questions every time.
NGSS-referenced: 3-PS2-1