In every investigation the independent variable is the one you change, the dependent variable is the one you measure, and control variables are kept the same. A hypothesis links them: 'If the acid is warmer, then the magnesium will react faster, because particles move faster.'
Variables can be continuous (any value, like temperature) or categoric (named groups, like type of metal). Control variables matter because any of them could change the result. If you cannot control one, such as room temperature, you should measure it and mention it when you discuss your results.
Worked example
Students time how long magnesium fizzes in acid at different temperatures. Name the three types of variable.
- Independent: the temperature of the acid.
- Dependent: the reaction time.
Answer:Control: the length of magnesium, the volume and concentration of acid.
Key words
- hypothesis
- a testable idea with a reason
- categoric
- in named groups
- continuous
- any value in a range
- control variable
- kept the same for a fair test
New questions every time.
NGSS-referenced: MS-ETS1-3