1. Identifying Variables & Designing Investigations

2. 4 Kinds of Variables  1. Independent Variable – something that is changed by the scientist  What is tested  What is manipulated  Mnemonic (memory aid): Independent var. = changed (tested)

3. 4 Kinds of Variables  2. Dependent Variable – something that might (or might not) be affected by the change in the independent variable  What is observed… what is measured  The data collected during the investigation  Mnemonic (memory aid): dependent var. = measured

4. 4 Kinds of Variables  3. Constants– something that is not changed  Allow for a “fair test”  Will be a multiple number of constants in any experiment  Mnemonic (memory aid): constant = no change (stays the same)

5. 4 Kinds of Variables  4. Control– the group that is used as a standard to compare other groups—it is NOT experimented on  Represents the “normal” conditions  Has nothing added or taken from  Not all experiments have a control  Mnemonic (memory aid): control = zero (nothing added or subtracted from it)

6. For Example:

7. 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.

8. Identify the variables in this investigation.

9. What was the independent variable?  Ages of the students  Different ages were tested by the scientist  The word “different” in the word problem gives a context clue that whatever follows is probably the independent var.

10. What was the dependent variable?  The time it to put the puzzle together  The time was observed and measured by the scientist  The word “timed” implies use of timer to measure the time passed, so that is the dependent var.

11. What was a constant?  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.  The word “same” is a context clue that what follows is a constant

12. What was the control, if there was one?  There was NO control in this experiment  All ages were compared against other ages  There WOULD have been a control if the experiment were set up as follows: - The puzzle selected for the experiment was designed to be done by a typical 9-year old student.  In this case, the 9-year old group would be the control (the group all others are compared to)

13. What type of data would be produced in this experiment?  The scientists will time how long it takes each student to finish the puzzle, using a watch, timer, or stopwatch.  Since the data is written down using definite numbers, the data produced is quantitative data.  The word “timed” is a context clue for the use of numbers, so the data produced is quantitative

14. Another example:

15. 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.

16. What are the variables in this investigation?

17. Independent variable:  Sizes of nails  These were changed by the scientist  The word “different” is a context clue that is followed by the words “sizes of nails”, the independent var.

18. Dependent variable:  Number of paper clips picked up  The number of paper clips observed and counted (measured)  The word “number” is a context clue that paper clips will be counted, as a measurement…so it is the dependent var.

19. Constants:  Battery, wire, type of nail  None of these items were changed  The word “a” before battery and type of nail are context clues that only 1 type of these are present… and the fact that no mention was made as to different types of wire were used is a context clue as well.

20. Was there a control in this experiment?  As before, there was NO control in this experiment  No one size of nail was mentioned as the “normal” or “usual” size used

21. One more:

22. The higher the temperature of water, the faster an egg will boil.

23.  Independent variable – temperature of water  Dependent variable – time to cook an egg  Constants– type of egg, pot, water, stove used  Control – No control unless it was done once with 0 eggs included— that WOULD be a control

24. OK, I was kidding before—but this really is the last one:

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

26.  Independent variable – depth of the water  Dependent variable – temperature  Constants– thermometer, same pond, when during day & which day measuring temperature was done  Control – there was NO control unless the surface (depth = 0) was included— surface temp. would be control

27. Designing Investigations

28. 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?

29. 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?