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A variable is something that can change. In mathematics, a variable is an unknown number, which we usually represent by 'x'. In science, however, the word 'variable' has a different use when doing an experiment, and there are three kinds of variables. Independent Variable This is the variable you are testing, or manipulating. For example, if you were trying to determine which type of laundry soap removes the most dirt, you would test a variety of different kinds of soap. The type of soap would be the independent variable, and you would change it each time you did the experiment. Dependent Variable This is the variable you are measuring. For example, when you test each type of laundry soap, you will measure how much dirt is left. The amount of dirt remaining each time you do the experiment would be the dependent variable. Controlled Variables These are variables that could affect the outcome of the experiment, if you let them. You must make these variables the same each time you do the experiment, so that you know they had no effect. For example, each time you test a laundry soap, you would use the same water temperature. It wouldn't be a fair test if one soap were used in very hot water, and another in cold water. Similarly, you would make sure that each sample of dirty clothing had the same amount of dirt, so that if one soap does a better job, you'll know it wasn't because there was less dirt. Other variables you might want to control in this example would be the amount of water used, the time spent washing, and the amount of soap used. You'll control these variables, by making them the same for every test, so you know they're not affecting the result. |