1. Scientific Method: Variables
Learning Target:
I can explain the cause and effect relationship between variables.

2. Variables The different types of variables are;
-Independent Variable Dependent Variable
Variables are the basis of all experiments

3. Independent Variable
It is what the scientist changes in the experiment.
It is the 1 and only thing that is changed on purpose in the experiment.

4. It is what is being measured in the experiment.
Dependent Variable
It is what is being measured in the experiment.
It changes as a result of the independent variable.

5. Constants are things that stay the same for all test groups.

6. Experimental Groups
The test groups that receive the independent variable.

7. Control Group The test group in which nothing is changed.
The results of the experimental groups are compared to the result of the control group.

8. Cause and Effect Relationship
The independent Variable and Dependent Variable have a cause and effect relationship.
The independent variable = CAUSE
The dependent variable = EFFECT

9. Identifying Variables in Questions
Scientific Questions contain both the independent variable and dependent variable.
It does not matter how the question is written, it will contain both the IV and the DV.

10. Indentifying Variables in Questions Example
What is the effect of the volume of music on how active animals are?
IV: Volume of Music DV: Animals Activity Level

11. Identifying Variables in Questions EXAMPLE
How does temperature affect a plants growth rate?
IV: Temperature DV: Plant growth rate

12. Identifying Variables in Hypotheses
All Scientific Hypotheses contain the independent and dependent variables.
In a hypothesis the independent variable is located after the IF and the Dependent Variables is located after the THEN.
This is because the IV is the Cause and the DV is the Effect.

13. Identifying Variables in Hypotheses EXAMPLE
If I increase the amount of time I run then my heart rate will increase.
IV: Amount of time Running DV: Heart Rate

14. Identifying Variable in Hypotheses EXAMPLE
If you increase the amount of chum in the water, then the number of sharks in the area will increase.
IV: Amount of Chum DV: Number of Sharks

15. Identifying Variables, groups and constants
Independent Variable: The variable the scientist changes on purpose.
Dependent Variable: The variable that is measured. It changes as a result of the independent variable.
Constants: The things that are kept the same for all test groups.
Control Group: The test group that does not receive the independent variable. There is no change made to this group.

16. Identifying Variables in Experiments Example
John wanted to know if different colors of light help plants grow faster. He takes four plants (all the same type) and sets them up underneath different colored lights. One will be a white light, one will be red, one will be blue and one will be green. Every day He watered them the same amount of water at the same time. He recorded how tall the plants were every week for a month.
What is the independent Variable? Color of Light
What is the dependent Variable? Plant Height
What are the constants?
1. Type of Plant
2. Amount of Light
3. Amount of Water
What is the control group? Plant under White Light

17. Identifying Variables in Experiments Example
Sally wants to see if drinking a lot of milk will affect how much you eat at dinner. Sally did her experiment over the course of 3 days. Sally would drink different amounts of milk each day before dinner, and would serve herself the same amount and same kind of food each day for dinner, she would then measure the amount of food she had eaten each day. Day 1 Sally did not drink any milk, Day 2 Sally drank 1 8oz glass of milk, and Day 3 Sally drank 2 8oz glasses of milk.
What is the independent Variable? Amount of milk she drinks
What is the dependent Variable? Amount of food Eaten
What are the constants?
1. Type of food served
2. Amount of food served
3. Person
What is the control group? Day 1- No milk

18. Identifying Variables in Experiments Example
 Mr. Johnson thinks that a special juice will increase the productivity of his workers. He creates two groups of 50 workers and assigns each group the same task (In this case, they are supposed to staple a set of papers). Group A is given the special juice to drink while they work. Group B is given water to drink while they work. After an hour, Mr. Johnson counts how many stacks of papers each group has made.
What is the independent Variable? Type of Drink
What is the dependent Variable? Number of Stacks of Papers
What are the constants?
1. Amount of Workers
2. Task
What is the control group? Group B- Water

19. Identifying Variables in Experiments Example
Larry plays baseball and he wants to know if he can hit farther using a wood bat then with his metal bat. Larry uses a pitching machine set at a specific speed to pitch to him for the entire experiment. He hits 3 balls with his metal bat and measures the distance they landed from home plate. He then reloads the same 3 baseballs into the pitching machine and hits the 3 balls with the wood bat and measures the distance they landed from home plate.
What is the independent Variable? Type of Bat
What is the dependent Variable? Distance the ball is hit
What are the constants?
1. Pitch Speed
2. Baseballs
3. Batter
What is the control group? Metal Bat

20. Identifying Variables in Experiments Example
A shopping mall wanted to determine whether the more expensive “Tough Stuff” floor wax was better at protecting against scratches than the “Steel Seal” floor wax they already use. One liter of each brand of floor wax was applied to separate sections of the main hall of the mall. The test sections were all the same size and were covered with the same kind of tiles. After 3 weeks the number of scratches in each of the test sections was counted.
IV: Type of Floor Wax
DV: Number of Scratches
Control Group: Steel Seal floor wax that they already use
Constants: amount of wax, size of section, kind of tile, amount of time.

21. Identifying Variables in Experiments Example
After learning about recycling, members of John’s biology class investigated the effect of various recycled products on plant growth. John’s lab group compared the effect of different aged grass compost on bean plants. Three flats of bean plants were grown for 5 days. After 5 days they were fertilized with the different composts. Flat 1 got 3 month old compost, Flat B got 6 month old compost and Flat C got no compost. The plants received the same amount of sunlight and water each day. At the end of 30 days the group recorded the height of the plants.
IV: Age of Compost
DV: Plant Height
Control Group: Flat C- no compost
Constants: type of plant, amount of sunlight, amount of water, amount of time grown.

22. Identifying Variables in Experiments Example
In chemistry class, Allen learned about how metals ruse. Allen wanted to know do different types of liquids cause iron to rust faster. Allen got 4 beakers, one with plain water, one with clear soda, one with apple juice and one with salt water. He placed 1 iron nail in each of the beakers. He measured the amount of rust on each nail every day for a week.
IV: Type of Liquid
DV: Amount of Rust
Control Group: Plain water
Constants: type of nail, amount of time

23. Identifying Variables in Experiments Example
Joanna read that certain perfume scents would agitate bees. She decided to test 3 different perfumes and observe the bees behavior. She placed a saucer containing the first perfume 3 meters away from the bee hive. She recorded the time required for the bees to emerge and made observations on their behavior. After a 30 minute recovery period she tested the second and third perfumes and a fourth saucer containing plain water. All experiments were conducted on the same day when the weather conditions were similar.
IV: Type of Perfume
DV: Bee Behavior
Control Group: Saucer of plain water
Constants: distance from bee hive, same day