1. Identifying Variables

2. Kinds of Variables
Independent Variable – something that is changed by the scientist
What is tested
What is manipulated
Changed on purpose to see what may happen

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

4. Kinds of Variables
Controlled Variable – a variable that is not changed
Also called constants
Allow for a “fair test”

5. The Bread Experiment
Let’s discuss variables, constants and controls using the bread experiment!

6. She explains that yeast releases a gas as it feeds on sugar.
Problem/Question
John watches his grandmother bake bread. He asks his grandmother what makes the bread rise.
She explains that yeast releases a gas as it feeds on sugar.

7. Problem/Question
John wonders if the amount of sugar used in the recipe will affect the size of the bread loaf?

8. Note: These variables will be defined in the next few slides.
Hypothesis
The hypothesis is an educated guess about the relationship between the independent and dependent variables.
Note: These variables will be defined in the next few slides.

9. Do you know the difference between the independent and dependent variables?

10. Independent Variable
The independent, or manipulated variable, is a factor that’s intentionally varied by the experimenter.
John is going to use 25g., 50g., 100g., 250g., 500g. of sugar in his experiment.

11. In this case, it would be the size of the loaf of bread.
Dependent Variable
The dependent, or responding variable, is the factor that may change as a result of changes made in the independent variable.
In this case, it would be the size of the loaf of bread.

12. Control Group
In a scientific experiment, the control is the group that serves as the standard of comparison.
The control group may be a “no treatment" or an “experimenter selected” group.

13. All experiments should have a control group.
The control group is exposed to the same conditions as the experimental group, except for the variable being tested.
All experiments should have a control group.

14. Control Group
Because his grandmother always used 50g. of sugar in her recipe, John is going to use that amount in his control group.

15. Constants
John has to keep all other factors the same so that any observed changes in the bread can be attributed to the variation in the amount of sugar.

16. Constants
The constants in an experiment are all the factors that the experimenter attempts to keep the same.

17. Can you think of some constants for this experiment?

18. Constants They might include:
Other ingredients to the bread recipe, oven used, rise time, brand of ingredients, cooking time, type of pan used, air temperature and humidity where the bread was rising, oven temperature, age of the yeast…

19. Another Example:

20. 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.

21. Identify the variables in this investigation.

22. What was the independent variable?
Ages of the students
Different ages were tested by the scientist

23. What was the dependent variable?
The time it to put the puzzle together
The time was observed and measured by the scientist

24. What was a 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.

25. Yet Another example:

26. 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.

27. What are the variables in this investigation?

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

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

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

31. Guess what? One more:

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

33. Independent variable – temperature of water
Dependent variable – time to cook an egg
Controlled variable – type of egg and amount of water

34. Last one: (I promise)

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

36. Independent variable – depth of the water
Dependent variable – temperature
Controlled variable – thermometer and pond

37. Designing Investigations

38. 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?

39. Variables Independent Variable- soap
Dependent Variable- size of bubble blown
Controlled Variable-water and type of soap
Amount of soap in water mixture
Size of the bubble blown with different amounts of soap in the water

40. 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?

41. Variables Independent Variable- length of fall
Dependent Variable-height of bounce
Controlled Variable- ball, surface, size of the ball
The length of the fall, different fall for each trial
The height of the bounce from the different lengths of the fall ~ the higher the height of the fall the higher the bounce