2Background 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?
3VariablesVariable – the factor in an experiment that can change
4Independent Variable Also known as the Manipulated Variable Independent Variable – the variable that is purposely changed by the experimenter
5Dependent Variable Also known as the Responding Variable Dependent Variable – the factor that might change as a result of changes in the manipulated variableGenerally what is measured in the experiment
6Controlling 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 variableThis is so you can be sure that any changes in the dependent variable are due to the changes in the independent variable.
7Example Problem – How Does Temperature Affect Plant Growth? Independent Variable – TemperatureDependent Variable – Plant GrowthControlling variablesSame kind of plantsIdentical containersSame type and amount of soilSame type and amount of fertilizerSame amount of waterSame lighting
8Control GroupScientists usually study groups of living or nonliving things in a controlled experiment.Experimental Group – a group whose conditions are being changedControl Group – a group whose conditions are not being changedThe purpose of a control group is to serve as a standard of comparison
9Example Experimental Group 25°C Control Group 20°C Grew 1cm after 3 weeksGrew 0.5cm after 3 weeks
10CheckpointYou 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 containerDependent Variable?The time it takes the water to freezeControlling variables?Same type, temperature, and amount of waterSame freezerSame material for both containers
11CheckpointResearchers want to determine the best temperature for storing batteries.Independent Variable?The storage temperatureDependent Variable?The hours of use after storageControlling Variables?Same kind of batterySame type of storage (moisture, light, etc.)Same expiration date on batteriesSame use of batteries in testing