Testing Our Hypothesis

1. Testing Our Hypothesis

2. What is a controlled experiment? • To test a hypothesis, a scientist may conduct a controlled experiment. • A controlled experiment tests only one factor at a time. • The one factor that is changed in a controlled experiment is called a variable. • This ensures that the results of the experiment are due to the one variable being investigated and not due to other variables. .

3. What does it mean to control the variables in an experiment? Keeping all the variables the same, except for the one you´re testing.

4. Example # 1 Problem: You want to find out the amount of light that will allow a plant to grow more. For your experiment you need? • soil • seeds • pot • water • fertilizer

5. Example # 1 In order to test which light will make the plant grow the most, you decide to place three pots in different places. • One next to the window • One in the center of the classroom • One behind the lockers

6. Example # 1 Do you remember what it means to control the variables in an experiment? Keeping all the variables the same except for the one you´re testing. • Discuss the following with a partner: • Which variables should we keep the same? • Why should we keep them the same? • What is the one variable we are going to change in the experiment?

7. Example # 2 Remember out experiment from last week where we were trying to find out which of the three liquids (water, soapy water, or alcohol) had the greatest surface tension? • Change partners and discuss the following: • Name three variables that you would keep the same. • Name the variable that you would change.

8. Kinds of variables There are three kinds of variables: • Independent Variable • Dependent Variable • Controlled Variable

9. Independent Variable • This is the variable that you are changing on purpose in the experiment. • It is also known as the manipulated variable. • It is the variable that you are testing. • In the example of our plant, which would be the independent variable?

10. Dependent Variable • This is the variable that changes as a result of the experiment. • It is also known as the responding variable. • It is the variable that is observed and measured in response to the independent variable. • In the example of the plant, which would be the dependent variable?

11. Controlled Variable • These are the variable that we keep constant (do not change) in an experiment. • There can be one or more controlled variables in an experiment. • In our example of the plant, which are our controlled variables?

12. There can also be a control group • A control group is used in an experiment. • There are usually two groups in any experiment, one group is experimented on, and the other group, the control group, isn't. • The control group is used to examine how the experiment affected those who participated.

13. Let´s Practice Fertilizer in soil increases flower production Identify the following: • Independent variable • Dependent variable • Two controlled variables

14. Let´s Practice Medicine A will reduce the incidence of headaches Identify the following: • Independent variable • Dependent variable • Two controlled variables

15. Let´s Practice If zinc tablets are taken, then the number of colds per year is reduced. Identify the following: • Independent variable • Dependent variable • Two controlled variables

16. Let´s Practice If water is present, then the number of bacteria in garbage bins increases. Identify the following: • Independent variable • Dependent variable • Two controlled variables

17. Let´s Practice Girls throw softballs further than boys. Identify the following: • Independent variable • Dependent variable • Two controlled variables

18. Keep practicing your variablesand you will be an expert in no time!