1. Variables, Constants, and Controls
Experimental Design
From Hypotheses to Conclusions

2. Learning Target #1 (Write it down)
I can understand and identify independent variables, dependent variables, constants, and controls.

3. Journal Question
03 Oct 2012, P.26
Two brands of paper towels are on sale at Target. They both have the same number of sheets but one brand costs $1.50 more.
Write a testable question that would help you decide brand you should buy.

4. Example Experiment
Imagine we perform an experiment on some plants. We “feed” one plant Coke and another plant water. We want to see which plant will grow faster.
We will use this example to help us understand experimental variables, constants, and controls in a controlled experiment.

5. Types of Variables Independent Variable (IV):
The variable that is changed by the scientist.
Dependent Variable (DV):
The variable that is being measured.
**The dependent variable DEPENDS on the independent variable.

6. Identify the Variables
Independent Variable (IV):
What would the Independent Variable be in the plant experiment?
Hint: What is being controlled/changed?
Dependent Variable (DV):
What would the Dependent Variable be in the plant experiment?
Hint: What is being measured?

7. Constants Only 1 independent variable is allowed for each experiment.
All other experimental variables MUST remain unchanged or constant.
Constants help you be sure of WHY something else did or did not change.
- What must be kept constant in the plant experiment?

8. Controls These are the normal or accepted parameters.
The control allows the scientist to compare their test results to a “norm” or normal group.
- In testing which liquids help plants grow faster, water would probably be used as the “norm” or CONTROL and soda would then be the independent variable (what is being changed).

9. Now read the following experiment and identify the independent and dependent variables, the constants and the control.
Elizabeth wanted to test if temperature affected how fast milk goes bad and curdles. She left 4 oz. of milk in a room temperature closet, a fridge, and an oven that was turned on low heat. She then measured how rotten the milk was after 10 days.
IV: ____________________________________
DV: ____________________________________
Constants: _______________________________
Control:_________________________________

10. SpongeBob Clean Pants
SpongeBob noticed that his favorite pants were not as clean as they used to be. His friend Sandy told him that
he should try using Clean-O detergent, a new laundry soap she found at Sail-Mart. SpongeBob made sure to wash one pair of pants in plain water and another pair in water with the Clean-O detergent. After washing both pairs of pants a total of three times, the pants washed in the Clean-O detergent did not appear to be any cleaner than the pants washed in plain water.

11. Practice What is the independent variable in this example?
What is the dependent variable in this example?
What are 2 constants in this experiment?
Is there a control group? If so, what is it?

12. Krusty Krabs Breath Mints
Mr. Krabs created a secret ingredient for a breath mint that he thinks will “cure” the bad breath people get from eating crabby patties at the Krusty Krab. He asked 100 customers with a history of bad breath to try his new breath mint. He had fifty customers (Group A) eat a breath mint after they finished eating a crabby patty. The other fifty (Group B) also received a breath mint after they finished the sandwich, however, it was just a regular breath mint and did not have the secret ingredient. Both groups were told that they were getting the breath mint that would cure their bad breath. Two hours after eating the crabby patties, thirty customers in Group A and ten customers in Group B reported having better breath than they normally had after eating crabby
patties.

13. Practice What is the independent variable in this example?
What is the dependent variable in this example?
What are 2 constants in this experiment?
Is there a control group? If so, what is it?

14. Journal Question
04 Oct 2012, P. 26
Write a hypothesis for mixing flour and water.
What are your independent and dependent variables?

15. Hypothesis The premise of your experiment.
An educated guess as to the outcome based on some information you already know or suspect.

16. Hypothesis If (this is done), then (this will happen).
If (independent variable), then (dependent variable) will happen.
If a plant is fed Coke, then it will grower faster than a plant fed water.

17. Writing a Hypothesis
If I drink Mountain Dew before bed, then I will not fall asleep quickly.
IV: Drinking Mountain Dew
DV: The amount of sleep

18. Practice Use the following hypotheses to identify the variables:
If I leave all the lights on all day,
then my electric bill will be expensive.
IV:______________________
DV:______________________

19. Practice If I brush my cat more, then there
will be less fur on my furniture.
IV:________________________
DV:________________________

20. Journal Question
09 Oct 2012, P. 28
The ingredients in bread are flour, milk, sugar, salt, butter, and yeast.
What happened to the bread dough as it sat out on the counter all day? Why do you think this happened?

21. Journal Question
10 Oct 2012, P. 27
What is the difference between a recipe and a procedure?
Today – Writing procedures

22. Procedures
A series of instructions directing how a task should be done.
Must include enough detail for others to be able to exactly repeat the task.
Convert the following recipe into an experimental procedure.

23. Mix together 1¼ cup milk, 2T sugar, 1½ t salt, 2T butter, and 2¼ t yeast in a large bowl.
Add 3 cups bread flour, one cup at a time, and mixing between each addition.
Knead dough until it is soft, smooth, and elastic. Put dough into a large, well greased bowl and cover with a damp cloth.
Allow dough to rise in a warm place until it has doubled in size. Punch down and place dough in a greased loaf pan, covered, to rise for 1 hour.
Bake in a pre-heated oven at 350°F for minutes.
Remove from loaf pan and cool on a wire rack.

24. Materials List of all supplies needed for the experiment.
Equipment
Ingredients
Chemicals
Supplies
These are always listed separately from the procedures.