Controlling Variables

Background Information Suppose that one of your friends keeps aquarium fish as pets. Last week, all of the fish in the aquarium died. When your friend got new fish, she decided to use a different aquarium filter, a different type of fish food, and a different temperature setting for the water. If the new fish survive, could she tell what caused the old fish to die?

Variables Variable – the factor in an experiment that can change

Independent Variable Also known as the Manipulated Variable Independent Variable – the variable that is purposely changed by the experimenter

Dependent Variable Also known as the Responding Variable Dependent Variable – the factor that might change as a result of changes in the manipulated variable Generally what is measured in the experiment

Controlling Variables In an experiment, all other factors except the independent variable must be controlled. Controlling variables means keeping all of the conditions the same except the independent variable This is so you can be sure that any changes in the dependent variable are due to the changes in the independent variable.

Example Problem – How Does Temperature Affect Plant Growth? Independent Variable – Temperature Dependent Variable – Plant Growth Controlling variables Same kind of plants Identical containers Same type and amount of soil Same type and amount of fertilizer Same amount of water Same lighting

Control Group Scientists usually study groups of living or nonliving things in a controlled experiment. Experimental Group – a group whose conditions are being changed Control Group – a group whose conditions are not being changed The purpose of a control group is to serve as a standard of comparison

Example Experimental Group 25°C Control Group 20°C Grew 1cm after 3 weeks Grew 0.5cm after 3 weeks

Checkpoint You are planning an experiment to find out whether the rate at which water freezes depends on the shape of the container. Independent Variable? The shape of the container Dependent Variable? The time it takes the water to freeze Controlling variables? Same type, temperature, and amount of water Same freezer Same material for both containers

Checkpoint Researchers want to determine the best temperature for storing batteries. Independent Variable? The storage temperature Dependent Variable? The hours of use after storage Controlling Variables? Same kind of battery Same type of storage (moisture, light, etc.) Same expiration date on batteries Same use of batteries in testing