What Is a Variable in Science?
Taught in US schools
Key Takeaways
- A variable is any factor in an experiment that can change.
- The independent variable is what the scientist changes on purpose.
- The dependent variable is what is measured - it depends on the independent variable.
- Controlled variables are kept the same in all trials to make the test fair.
What Is a Variable in Science?
A variable is any factor in a scientific experiment that can change or vary. Controlling and measuring variables is what makes a scientific experiment valid - rather than just an uncontrolled observation.
Understanding variables is essential to the scientific method, because poorly controlled experiments produce unreliable results.
The Three Types of Variables
Independent Variable (IV) The factor the scientist deliberately changes from trial to trial. The cause.
"I want to test how ramp height affects how far a ball rolls. I will change the height of the ramp." Independent variable = ramp height
Dependent Variable (DV) The factor the scientist measures to see the effect of the independent variable. The effect - it "depends on" what happens to the independent variable.
"I will measure how far the ball rolls after going down the ramp." Dependent variable = distance the ball rolls
Controlled Variables (Constants) All other factors that the scientist keeps the same in every trial. These ensure that any change in the dependent variable is caused by the independent variable - not something else.
"To make the test fair, I will use the same ball, the same surface, release the ball from the same starting point, and measure the distance the same way each time." Controlled variables = ball type, surface, release method, measurement method
Why Controlled Variables Matter: The "Fair Test"
Imagine testing whether ramp height affects ball distance - but you accidentally used a heavier ball on the high ramp than on the low ramp. Did the ball roll farther because the ramp was higher, or because the ball was heavier? You can't tell. The experiment was not a fair test.
A fair test changes only ONE variable (the independent variable) while keeping everything else constant. This is the only way to draw valid conclusions from experimental results.
Variables in Real Experiments
Do plants grow taller with more water?: Amount of water - Plant height - Soil type, light, temperature, pot size, plant species
Does salt water boil faster than plain water?: Type of water - Time to boil - Amount of water, heat source, pot size, starting temperature
Which paper airplane design flies farthest?: Paper airplane design - Distance flown - Paper type, thrower, throwing technique, location
Practice Activities
- Given a question, students identify the IV, DV, and 3+ controlled variables before designing the experiment.
- "Variable error" scenarios: give students an experiment description with an uncontrolled variable. Can they find the flaw? "A student used a plastic ramp for the low height and a wooden ramp for the high height. What's wrong with this experiment?"
- After conducting an experiment, students write: "My independent variable was ___, my dependent variable was ___, and I controlled ___ by keeping it the same every time."
- Connect to real-world science: "In a drug trial, why do some people get the real medicine and some get a placebo?" (The control group controls for the expectation of getting better.)
Frequently Asked Questions
What is a variable in a science experiment?
A variable is any factor, condition, or element in an experiment that can change or vary. To conduct a fair and reliable experiment, scientists identify three types of variables: the independent variable (what they intentionally change), the dependent variable (what they measure to see the effect), and controlled variables (everything else they keep the same across all trials).
What is the independent variable?
The independent variable is the one factor that the scientist deliberately changes in an experiment. It is the 'cause' in a cause-and-effect relationship. Example: In an experiment testing how ramp height affects the distance a ball rolls, the ramp height is the independent variable - it's the thing the scientist changes from trial to trial.
What is the dependent variable?
The dependent variable is what the scientist measures to see the effect of changing the independent variable. It is the 'effect' in a cause-and-effect relationship. Example: In the ramp experiment, the distance the ball rolls is the dependent variable - it changes depending on the ramp height. A helpful memory trick: the dependent variable 'depends on' the independent variable.
Free Variable Worksheets
Curriculum-aligned printable worksheets for 3rd – 5th Grade. Download free.