Variables, Constants, and Controls

Variables, Constants, and Controls

Experimental DesignFrom Hypotheses to Conclusions

Learning Target #1

(Write it down)

I can understand and identify independent variables, dependent variables, constants, and controls.

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.

Example ExperimentImagine 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.

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.

Identify the VariablesIndependent 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?

• 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?

Constants

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).

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:_________________________________

SpongeBob Clean PantsSpongeBob noticed that his favorite pants were not as clean as they used to be. His friend Sandy told him thathe 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.

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?

Krusty Krabs Breath MintsMr. 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 crabbypatties.

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?

Journal Question

• 04 Oct 2012, P. 26

• Write a hypothesis for mixing flour and water.– What are your independent and

dependent variables?

Hypothesis• The premise of your experiment.

• An educated guess as to the outcome based on some information you already know or suspect.

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.

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

PracticeUse 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:______________________

If I brush my cat more, then there will be less fur on my furniture.

IV:________________________DV:________________________

Practice

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?

Journal Question• 10 Oct 2012, P. 27

• What is the difference between a recipe and a procedure?

• Today – Writing procedures

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.

• 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 20-25 minutes.

• Remove from loaf pan and cool on a wire rack.

Materials• List of all supplies needed for the

experiment.– Equipment– Ingredients– Chemicals– Supplies

• These are always listed separately from the procedures.