Scientific Method - Controls and Variables

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Scientific Method - Controls and Variables
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Scientific Experiments Follow Rules.

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

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Manipulated and Responding Variables?

• The factor that is changed is known as the
  manipulated variable.
• The factor that is measured or observed is called
  the responding variable.
• What are the manipulated and responding variables
  in your E. coli experiment?

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Control Variables?

• The experimenter makes a special effort to keep
  other factors constant so that they will not
  effect the outcome.
• Those factors are called control variables.
• What are some of the control variables in your E.
  coli experiment?

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Experimental Control?

• The experimenter needs to be able to see if the
  thing they manipulated had an effect on the
  outcome of the experiment.
• They do this by comparing to an identical
  experiment where the manipulated variable was
  either missing or remained unchanged.
• This is the Experimental Control.
• What is the experimental control in your E. coli
  experiment?

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What is the purpose of an Experimantal Control?

• Controls are NOT being tested.
• Controls are used for COMPARISON

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An example of Controls Variables

• 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 in Your Experiment?

• Varying the route is the manipulated variable
• The time it takes is the responding variable
• Keeping the same walker throughout makes the
  walker a control variable. Name some others.
• You pick one route to be the experimental control
  and compare the other routes to it.

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• One more thing it is best to make several trials
  with each manipulated variable.
• This gives you an increased confidence in your
  data.

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