1. Experimental Design & Identifying Variables

2. Fair Test  Changing only one factor and keeping all the other conditions the same.  An experiment in which the only variables that change are the one you are changing to test and the one you are measuring as a result of that change.

3. 3 Kinds of Variables  Independent Variable (IV) – something that is changed by the scientist  What is tested  What is manipulated

4. 3 Kinds of Variables  Dependent Variable (DV) – something that might be affected by the change in the independent variable  What is observed  What is measured  What is responding to the independent  The data collected during the investigation

5. 3 Kinds of Variables  Controlled Variable (CV)– a variable that is not changed  Also called constants  Allow for a “fair test”

6. Control Group  The participant(s) being tested that do not get the treatment  You leave them alone to use as a comparison group

7. For Example:

8. Scenario 1  Elizabeth wanted to test if temperature affected how fast milk goes bad and curdles. She left 50 mL of 2 % milk in a room temperature closet, a fridge, and a oven that was turned on low heat. She then measured how much the milk curdled after 24 hours.

9. Identify the variables in this investigation.

10. What was the independent variable?  Temperature of Milk  The milk was placed in rooms with different temperature.

11. What was the dependent variable?  Measured how much the milk curdled.

12. What was a controlled variable(s)?  2% Milk for each different temperature  50 mL of milk for each temperature  Each temperature was checked after 24 hours had passed.

13. Another example:

14. Scenario 2  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.

15. What are the variables in this investigation?

16. Independent variable:  Sizes of nails  These were changed by the scientist

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

18. Controlled variables:  Battery, wire, type of nail  None of these items were changed

19. One more:

20. Scenario 3  How does the temperature of the starting water affect how fast an egg will boil?

21.  Independent variable – temperature of water  Dependent variable – time to cook an egg  Controlled variable – type of egg

22. Last one:

23. The temperature of water was measured at different depths of a pond.

24.  Independent variable – depth of the water  Dependent variable – temperature  Controlled variable – thermometer

25. Designing Investigations

26. The greater the amount of soap in a soap and water mixture, the bigger a soap bubble can be blown.  Design an investigation to test this hypothesis.  Identify the variables  What exactly will be changed? How will it be changed?  What exactly will be measured? How will it be measured?

27. The farther a ball drops, the higher it will bounce.  Design an investigation to test this hypothesis.  Identify the variables  What exactly will be changed? How will it be changed?  What exactly will be measured? How will it be measured?