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Scientific Method - Scientific Method - Controls and VariablesControls and Variables

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Scientific Experiments Scientific Experiments Follow RulesFollow Rules..

• An experimenter changes one factor and observes or measures what happens.

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The Control VariableThe Control Variable•The experimenter makes a The experimenter makes a

special effort to keep special effort to keep other factors constantother factors constant so so that they will not effect that they will not effect the outcome.the outcome.

• Those factors are called Those factors are called control variables.control variables.

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What is the Purpose of What is the Purpose of a Control?a Control?

•Controls are NOT being tested

•Controls are used for COMPARISON

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Other Variables•The factor that is changed is

known as the independent variable.

• The factor that is measured or observed is called the dependent variable.

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Example of Controls & Example of Controls & Variables #1Variables #1

• For example, suppose you want to figure out the fastest route to walk home from school. You will try several different routes and time how long it takes you to get home by each one.

• Since you are only interested in finding a route that is fastest for you, you will do the walking yourself.

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What are the Variables What are the Variables in Your Experiment?in Your Experiment?

• Varying the route is the Varying the route is the independent variableindependent variable

• The time it takes is the The time it takes is the dependent variabledependent variable

• Keeping the same walker Keeping the same walker throughout makes the walker a throughout makes the walker a control variable.control variable.

Example 2

• The higher temperature of water, the faster an

egg will boil.

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• Independent variable: temperature of water

• Dependent variable: time to cook an egg

• Control variables: type of egg, stove, amount of water, type of pan

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Examples #3

• One tank of gold fish is fed the normal amount of food once a day, a second tank is fed twice a day, and a third tank four times a day during a six week study. The fish’s weight is recorded daily.

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• Independent variable: amount of food

• Dependent variable: Fish’s weight

• Control GROUP: Group fed the normal amount of food.

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