Variable: The component in an experiment that can change. There are two types of variables called responding variables and manipulated variables.
Manipulated variable (independent variable): The variable in an experiment that you change on purpose to test your hypothesis.
Responding variable (dependent variable): The variable in an experiment that changes as a result of (in response to) the manipulated variable.
Control group: The group in which the variable is not changed so that you have a baseline to compare your experimental data to.
Example: I hypothesize that my sled will go down the hill faster if I wax the bottom of it. I set up an experiment to test this hypothesis. First I ride down the hill 10 times with the sled un-waxed and find my average speed of those 10 trials. Then I wax the bottom of the sled and slide down 10 more times and find my average speed again.
Manipulated variable: the texture of the bottom of the slide (waxed vs. un-waxed)
Responding variable: speed of the sled down the hill
