# Scientists Say: Variable

## A variable is something that can be changed

The word “variable” can be an adjective or a noun. As an adjective, it means able to vary, or change. As a noun, the word refers to something that can be changed. That thing may be a quantity that can take on different values. Or, it may be a factor in an experiment that someone changes.

In math, a variable is a symbol that stands in for an unknown value. It is usually a letter, such as x or y. A variable’s value changes depending on the context. Solving the equation x + 1 = 3, for instance, finds that x = 2. In the equation x + 2 = 5, meanwhile, x = 3. And in the equation x + 1 = y, plugging in different values for x results in different values for y.

Science experiments also involve variables. In an experiment, a person can change one thing and see how that may impact another thing. The factor that a person changes is the independent variable. The thing that may change in response to that is the dependent variable. But a dependent variable may be affected by other things, too. So, a scientist tries to keep those external factors — or controlled variables — constant. That way, they won’t impact the experiment’s outcome.

#### In a sentence

In a study of the five-second rule, the independent variable is how long food lies on the floor.

Maria Temming is the assistant editor at Science News for Students. She has bachelor's degrees in physics and English, and a master's in science writing.