Parts of an investigation

Define and use the following vocabulary:

Variables, constants, objective, hypothesis, control, and methodology

What is methodology?

'ology' means the study of something

'Methods' refers to the experimental design, which includes the variables, constants, methods section, etc. This is how you have designed the experiment and taken into account all of the details that allow you to achieve accurate results that others can replicate, or copy.

Skill 1: I can identify independent variables, dependent variables, and constants.

Variable = change

a factor that changes between test groups

Ex: Plant A receives 100 ml of water per day, while Plant B receives only 50 ml. Since the amount of water changes between groups, it is a variable.

Constant = unchanging

a factor that stays the same between test groups

Ex: Plant A and Plant B are planted in 150 mg of soil and receive 8 hours of sunlight per day. Since the amount of soil and sunlight are the same between groups, they are constants.

Do this in your science notebook!

"Variable and constant" practice problems

For each statement, identify the two variables. Name two constants for each experiment. Constants are not listed. You have to think about it and figure them out.

1. A study was done to find if different tire treads affect the braking distance of a car.

2. The time it takes to run a mile depends on the person’s running speed.

3. The height of bean plants depends on the amount of water they receive.

4. The higher the temperature of the air in the oven, the faster a cake will bake.

5. Lemon trees receiving the most water produced the most lemons.

Independent variable: The factor I choose to test. I do this differently with each test group.

(synonym: manipulated variable)



Dependent variable: The results or data collected

(synonym: responding variable)

Mnemonic: I'm a Dr.

Independent variable & manipulated variable = I'm

Dependent variable & responding variable = Dr

When you look at the graph of the results of an experiment, you are looking at the relationship between the two variables. Usually, the independent variable is on the x-axis and the dependent variable is on the y-axis. The graph shows how the independent variable affects the dependent variable, or makes it change.

Do this in your science notebook!

1. Using the graph, complete the following sentence. ______________ affects ______________.

2. What is the independent variable in the graph above? _____________________________

3. What is the dependent variable in the graph above? ______________________________

4. Look at the 5 "variable and constant" practice problems above and determine which variable is dependent and which is independent. Just write 'IV' above the independent variable and 'DV' above the dependent variable.


Ask for the answer key. Ask questions if you got any wrong.

Skill 2: Identify the objective statement or hypothesis.

The objective is the purpose, or target, of the experiment. You want to see if the independent variable (IV) affected the dependent variable (DV). The hypothesis states the objective and usually predicts the outcome.

Example: Will the height of a plant be affected by how much water it receives?

My goal is to give plants a different amount of water (IV) and see if they grow taller (DV). I predict that the plants with more water will grow taller.


Do this in your science notebook!

Pick three scenarios from the "variable and constant" practice problems and write the objective of the experiment in a question form.

Skill 2: Check your answers with a teacher.

Skill 3: Correctly identify the control group. (This is the group your compare your results to.)

I wonder if the plant will grow taller if it gets fertilizer.

Hypothesis: If the plant gets fertilizer, it will grow taller.

Plant A gets 100 ml of water per day, plus fertilizer

Plant B gets 100 ml of water per day, without fertilizer

The control group allows you to compare the results at the end of the experiment to see if the independent variable affected the dependent variable. The control does not have the independent variable applied to it, in this case, fertilizer. Other groups are called 'test groups' because the IV is tested on them.

Do this in your science notebook!

Pick two scenarios from the "variable and constant" practice problems to find the control group for. Sometimes, you just have two groups to compare at the end of the experiment.

Example 1: I will compare the braking distance from one type of tire tread to the braking distance with another type of tire tread. (You may not use this example!)


Skill 3: Check your answers with a teacher.

Click here to take the skills 1-3 formative quiz before moving to the next page.