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

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

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.

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.

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

Experimental Groups The test groups that receive the independent variable.

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.

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

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.

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

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

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.

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

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

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.

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

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

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

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