# 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.