Scientific Variables

Scientific Variables

Middle School

​

Learning Objectives

• Define independent, dependent, and control variables in an experiment.

• Differentiate between the three types of scientific variables.

• Identify the variables in a given experimental scenario.

• Understand the relationship between independent and dependent variables.

Key Vocabulary

​

Control Variable

An element in an experiment that is kept unchanged and unaffected by the other variables.

​

Independent Variable

The variable that is deliberately changed by the scientist to observe the effect it has.

​

Dependent Variable

The variable that is tested and measured, which depends on the independent variable's changes.

​

​

What Is a Control Variable?

• A control variable is a factor kept constant throughout an experiment.

• ​It creates a baseline for comparing the results of your experiment.

• This ensures a fair test by isolating the independent variable’s effects.

• For instance, soil type and pot size are controls in a plant experiment.

​

Multiple Choice

Why must most variables be kept constant in an experiment?

• To make the experiment last longer.

• To change the dependent variable.

• To have more things to measure.

• To know which variable was responsible for the observed results.

​

​

The Independent Variable

• This is the single factor that a scientist deliberately changes or manipulates.

• It stands alone and is not affected by other variables in an experiment.

• This variable is the cause in a cause-and-effect relationship, influencing the outcome.

• On a graph, the independent variable is always plotted on the x-axis.

​

Multiple Choice

A student is testing how the mass of a ball affects the distance it rolls. What is the independent variable?

• The distance the ball rolls

• The mass of the ball

• The ramp it rolls down

• The surface it rolls on

​

​

What Is a Dependent Variable?

• This is what a scientist measures or observes in an experiment.

• Its value depends on changes to the independent variable.

• It represents the outcome or effect that is being measured.

• On a graph, it is plotted on the vertical y-axis.

Multiple Choice

In an experiment testing which brand of bubblegum allows you to blow the largest bubble, what is the dependent variable?

• The size of the bubble

• The brand of bubblegum

• The flavor of the gum

• The person blowing the bubble

​

Common Misconceptions

Misconception	Correction
Experiments can have multiple independent variables.	A fair test changes only one independent variable at a time.
The control variable is the same as the control group.	A control variable is kept constant; a control group is for comparison.
The dependent variable is what you change.	The dependent variable is the effect you observe or measure.

Multiple Choice

A study aims to determine the effect of the amount of water on the sprouting of a mongo seed. How are the 'amount of water' and 'sprouting of mongo seeds' related?

• The amount of water is the dependent variable, and the sprouting is the independent variable.

• Both are dependent variables.

• Both are control variables.

• The amount of water is the independent variable, and the sprouting is the dependent variable.

Multiple Choice

In the statement 'A student's grade depends on how much she studies,' why is 'how much she studies' considered the independent variable?

• Because it depends on the student's grade.

• Because it is the factor that is being changed or manipulated.

• Because it is the outcome being measured.

• Because it is kept constant throughout.

Multiple Choice

A scientist is testing how different types of soil (sandy, clay, loam) affect the height of a sunflower. To ensure the results are valid, what are two critical variables that must be kept constant?

• The amount of sunlight and the type of soil.

• The amount of sunlight and the amount of water.

• The type of soil and the height of the sunflower.

• The height of the sunflower and the amount of water.

Multiple Choice

In the experiment testing whether classroom temperature affects test scores, classroom temperature is an example of which type of variable?

• Dependent variable

• Independent variable

• Confounding variable

• Control variable

​

Summary

• The independent variable is the one factor you purposely change in an experiment.

• The dependent variable is the factor you measure to see the results.

• Control variables are all factors that are kept the same for a fair test.

• The independent variable (x-axis) affects the dependent variable (y-axis) on a graph.

Poll

On a scale of 1-4, how confident are you about identifying variables in an experiment?

• 1

• 2

• 3

• 4