1. Identifying Variables & Designing Investigations

2. First: a review of the Scientific method:
Steps:
Observations/Problem
Research
Hypothesis development
Experiment
Data (and analysis)
Conclusion

3. A proper hypothesis: Based on research Must be testable
Typically is an if, then statement
“educated guess”

4. Experimental Design
The experiment must be carefully designed to only test ONE variable at a time.
A variable is ANYTHING that changes or can be manipulated in an experiment.

5. 3 Kinds of Variables
Independent Variable (AKA: manipulated variable)– something that is changed by the scientist
What is tested
What is manipulated
The variable that is changed by the scientist on purpose; the ‘I control’ variable

6. 3 Kinds of Variables
Dependent Variable (AKA: responding variable) – something that might be affected by the change in the independent variable
What is observed and/or measured
The variable that might change because of what the scientist changes – what is being measured
the “GOD” variable…variable out of YOUR control.

7. 3 Kinds of Variables
Controlled Variable – a variable that is not changed
Also called constants
Allow for a “fair test”
A standard for comparison.

8. When graphing data:
Independent variable (the one you control) goes on X axis.
Dependent variable (the one you are measuring a change in) goes on the y axis.

9. For Example:

10. Students of different ages were given the same jigsaw puzzle to put together. They were timed to see how long it took to finish the puzzle.

11. Identify the variables in this investigation: - independent - dependent - control

12. Ages of the students Independent variable
Different age groups were chosen and tested by the scientist

13. The time it took to put the puzzle together
Dependent variable
The time it took to put the puzzle together
The time was observed and measured by the scientist.
This is not something the scientist had control over…it was the “God variable” because it was out of the control of the scientist.

14. What was the controlled variable?
Same puzzle
All of the participants were tested with the same puzzle.
It would not have been a fair test if some had an easy 30 piece puzzle and some had a harder 500 piece puzzle.

15. Another example:

16. An investigation was done with an electromagnetic system made from a battery and wire wrapped around a nail. Different sizes of nails were used. The number of paper clips the electromagnet could pick up was measured.

17. Independent variable:
Sizes of nails
These were changed by the scientist on purpose.

18. Number of paper clips picked up
Dependent variable:
Number of paper clips picked up
The number of paper clips observed and counted (measured)

19. Controlled variables:
Battery, wire type/thickness,
None of these items were changed