1. Three Kinds of Variables A study in variables and the scientific method.

2. Variables Independent/Manipulated variable is a factor or condition that is intentionally changed by an investigator in an experiment. Dependent/Responding variable is a factor or condition that might be affected as a result of changing the independent variable. Controlled variable is a variable that is not changed.

3. Example A student wanted to test how the mass of a paper airplane affected the distance it would fly. Paper clips were added before each test flight. As each paper clip was added, the plane was tested to determine how far it would fly. The mass of the plane(number of paper clips added) was the independent/manipulated variable. The dependent/responding variable was the distance flown. A controlled variable in the experiment was the fact that the same plane was used for each trial.

4. Scenario #1 Two groups of students were tested to compare their speed working math problems. Each group was given the same problems. One group used calculators and the other group computed without calculators. What are the: - Independent/Manipulated - Dependent/Responding - Controlled variables in this situation?

5. Scenario #1 - Independent/Manipulated Variable - Using or not using calculators - Dependent/Responding Variable - Time to complete math problems - Controlled Variable - Same math problems

6. Scenario #2 Students of different ages were given the same puzzle to assemble. The puzzle assembly time was measured. What are the: - Independent/Manipulated - Dependent/Responding - Controlled variables in this situation?

7. Scenario #2 - Independent/Manipulated Variable - Ages of the students - Dependent/Responding Variable - Time to assemble puzzle - Controlled Variable - Same puzzle

8. Scenario #3 A study was done to find if different tire treads affect the braking distance of a car. What are the: - Independent/Manipulated - Dependent/Responding variables in this situation?

9. Scenario #3 - Independent/Manipulated Variable - Different tire treads - Dependent/Responding Variable - Braking distance

10. Controlled variables There can be several controlled variables. If an experiment is to be useful, only one variable at a time can be manipulated intentionally. All other variables must be controlled throughout all parts of the experiment. If more than one variable is altered, the results of an experiment cannot be interpreted with any validity.

11. Scenario #4 An experiment was performed to determine how the amount of coffee grounds could affect the taste of coffee. The same kind of coffee, the same percolator, the same amount and type of water, the same perking time, and the same electrical source were used. What are the: - Independent/Manipulated - Dependent/Responding - list 3 Controlled variables in this situation?

12. Scenario #4 - Independent/Manipulated Variable - Amount of coffee grounds - Dependent/Responding Variable - Taste - Controlled Variable - Same kind of coffee - Same percolator - Same amount and type of water - Same perking time - Same electrical source

13. Scenario #5 A study was done with an electromagnet system made from a battery and wire wrapped around a nail. Different sizes of nails were used and the number of paper clips that the electromagnet could pick up was measured. What are the: - Independent/Manipulated - Dependent/Responding - list 3 Controlled variables in this situation?

14. Scenario #5 - Independent/Manipulated Variable - Size of nail - Dependent/Responding Variable - Number of paper clips picked up - Controlled Variable - Same battery - Same wire - Same paper clips

15. Scenario #6 The number of pigs in a litter is determined by the weight of the mother pig. What are the: - Independent/Manipulated - Dependent/Responding - Controlled variables in this situation?

16. Scenario #6 - Independent/Manipulated Variable - Mother pig’s weight - Dependent/Responding Variable - Number of piglets - Controlled Variable - Same type of pigs - Same living spaces - Same food

17. Scenario #7 The State Agriculture Department has been counting the number of foxes in Harris County. Will the number of foxes have any effect on the rabbit population? What are the: - Independent/Manipulated - Dependent/Responding variables in this situation?

18. Scenario #7 - Independent/Manipulated Variable - Number of foxes - Dependent/Responding Variable - Number of rabbits

19. Scenario #8 The score on the final test depends on the number of basic skills learned. What are the: - Independent/Manipulated - Dependent/Responding variables in this situation?

20. Scenario #8 - Independent/Manipulated Variable - Basic Skills - Dependent/Responding Variable - Scores on tests

21. Scenario #9 A study was done with white rats to see if the number of offspring born dead was affected by the number of minutes exposure to X-rays by the mother rats. What are the: - Independent/Manipulated - Dependent/Responding variables in this situation?

22. Scenario #9 - Independent/Manipulated Variable - Exposure to X-rays - Dependent/Responding Variable - Number of dead offspring