Same Science › Planning investigations › Independent and dependent variables
What are independent and dependent variables?
Every experiment has three kinds of variables. The independent variable is the one thing you change on purpose (hours of light). The dependent variable is what you measure to see the effect (plant height). Controlled variables are everything you keep the same so the test is fair (water, soil, pot size). Some classes say manipulated and responding instead.
- Independent: what you change. Only one.
- Dependent: what you measure. It depends on the change.
- Controlled: what you keep the same.
Why schools teach it
The vocabulary of every experiment
Students plan and carry out investigations from third grade on, identifying the variables and controls (NGSS science practice 3). The words return in every lab, every science fair project and every graph.
Naming the variables first prevents the most common mistake: changing two things at once.
At the kitchen table
What to say, and what to skip
Say this
What are you changing on purpose?
That's independent.What are you measuring?
That's dependent.What has to stay the same?
List at least two controls.Does what you measure depend on what you change?
That's the check.
Skip this
- Mixing up independent and dependent.Ask: which one did you choose, and which one did you find out?
- Changing more than one thing.Then you can't tell which one caused the result.
- Forgetting the units.Height in cm, time in seconds.
See it in action
Do heavier balls roll farther down a ramp?
Independent
the mass of the ballDependent
how far it rolls (cm)Controlled
ramp height, ramp surface, ball size, release point
A trick: the dependent variable “depends on” the independent one.
Free practice sheet
Make a variables sheet
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Parents also ask
What are manipulated and responding variables?
The same things: manipulated is independent, responding is dependent.
What's a control group?
A group that doesn't get the change, like plants with no fertilizer, to compare against.
Is a controlled variable the same as a constant?
Yes. Some classes say constants.
Can there be two dependent variables?
Yes, you can measure two things. But change only one independent variable.