Scientific Method - Controls and Variables

1. Scientific Method - Controls and Variables

2. Scientific Experiments Follow Rules. • An experimenter changes ONE factor and observes or measures what happens.

3. 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?

4. 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?

5. 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?

6. What is the purpose of an Experimantal Control? • Controls are NOT being tested. • Controls are used for COMPARISON

7. 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.

8. 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.

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