What is a variable?
A variable is anything in an experiment that can change or be measured. To make a test fair, scientists control the variables carefully. There are three important kinds.
The three variables
- Manipulated variable — the one thing you change on purpose. For example, the length of a plant's watering time.
- Responding variable — what you measure to see the result. For example, the height the plant grows.
- Constant (fixed) variable — everything you keep the same so the test is fair, such as the type of plant, the pot size and the amount of sunlight.
Key idea
Change ONE thing (manipulated), measure ONE thing (responding), and keep everything else the SAME (constant). This makes the experiment fair.
Why fair tests matter
If you change more than one thing at a time, you cannot tell which change caused the result. Keeping the constant variables the same means the result must come from the one thing you changed.
Example
Testing how sunlight affects plant growth: manipulated = hours of sunlight; responding = height of plant; constant = same plant, same water, same soil.