Temperature can have an infinite number of values between two points.

Variable is a term used to describe something that can be measured and can also vary. The opposite of a variable is a constant. A constant is a quantity that does not change within a specific context. In scientific experiments, variables are used as a way of grouping data. Variables can be grouped as discrete or continuous variables.

The second hand of a clock is in continuous motion.

Generally, variables are characteristics of a group of objects or events that can be measured in many different numerical values. Discrete variables can only have a certain number of different values between two given points. For example, in a family there can be one, two or three children, but there cannot be a continuous scale of 1.1, 1.5 or 1.75 children.

Continuous variables can have an infinite number of different values between two given points. As shown above, there cannot be a continuous scale of children within a family. However, if height were being measured, the variables would be continuous, as there are an unlimited number of possibilities, even if only looking at between 1 and 1.1 meters.

It is important to remember that both types of variables are grouped based on the scale used to measure them and what is being measured. In most scientific experiments, a discrete scale is used to measure both types of variables. Since there are an infinite amount of possibilities, this means that measurements of continuous variables are often rounded to make the data easier to work with.

Both discrete and continuous variables can take on one of two roles in a science experiment. During an experiment, the scientist often wants to observe the results of changing a variable. Often only one variable is changed, as it would be difficult to determine what caused the relevant response if multiple variables were influenced.

The variable that is manipulated by the scientist is the independent variable, while the dependent variable is the one that responds to change. In other words, the response of one variable depends on changes in the other variable. If there was no initial change in any of the variables, there would be no response from the dependent variable.

For example, during an experiment, the amount of light shining on a plant is changed. The amount of light would be the independent variable. To make repeatable measurements, the independent variable is likely to be a discrete variable, such as one hour, two hours, or three hours of light. The response of the plant, how much it grows or the direction in which it grows, will be the dependent variable. Since the amount of plant growth can be an infinite number of outcomes, it is a dependent continuous variable.