Controls and Variables

A variable is any factor that you change in the experiment.  The science fair experiment is a controlled experiment.  You are keeping all the factors except ONE the same (or constant).

CONTROLLED VARIABLES  are the variable(s) in the experiment that you are keeping the SAME throughout the experiment. 

An INDEPENDENT VARIABLE (also known as the  manipulated variable) is a factor that you change ON PURPOSE - you are testing the variable in an experiment!

For Example, if you wanted to test the following hypothesis: 

Hypothesis:  If 25 mL of salt is added to 100 mL of tap water, then the water will take longer to freeze than 100 mL of tap water with no salt added.

You would set up the experiment to test Salt Water vs. No Salt Water.  You want to keep as many of the variables THE SAME as possible.

Control Group:  One container with 100 mL of tap water.

Controlled Variables (the variables you are keeping the same in the experiment)

Independent Variable:  The amount of salt added to the water (25mL)

Other Controlled Variables:  The amount of water (100 mL)

                                             The type of water (tap water)

                                             The temperature of the water (room temperature)