Independent and Dependent Variables in Science

Independent and Dependent Variables in Science

Middle School

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Learning Objectives

• Learn the difference between independent and dependent variables in an experiment.

• Find the independent variable, dependent variable, and constants in a science experiment.

• Understand how to show independent and dependent variables on a science graph.

• Write a testable hypothesis using the 'If... then...' sentence structure.

Key Vocabulary

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Independent Variable

The factor that is intentionally changed by the experimenter to test its effects on the outcome.

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Dependent Variable

The factor that is measured or observed in an experiment to see how it responds to change.

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Constants

All the factors that are intentionally kept the same and unchanging throughout an entire experiment.

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Control Group

The group in an experiment that does not receive the experimental treatment and is used for comparison.

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Hypothesis

A testable prediction about the relationship between variables, often written as an 'If... then...' statement.

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Independent vs. Dependent Variables

Independent Variable

• ​The one factor that an experimenter decides to change on purpose.

• ​​It is what you are testing and is thought of as the cause.

• ​For example, the amount of water given to a plant is the independent variable.

Dependent Variable

• ​The factor that responds to the change, which the experimenter will then measure.

• ​​It is the result of the experiment and is thought of as the effect.

• ​For example, the height of a plant is the dependent variable in this experiment.

Multiple Choice

An independent variable is what the experimenter _____, while the dependent variable is what the experimenter _____.

• measures; keeps the same

• keeps the same; changes

• measures; changes

• changes; measures

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Controls and Constants in Experiments

Control Group

• The control group is the part of the experiment that is not changed.

• It is used as a baseline to compare the results against.

• For example, a plant that does not get any music is the control.

Controlled Variables

• These are factors that are kept the same for all groups in an experiment.

• Keeping these factors the same ensures that the experiment is a fair test.

• Examples include using the same soil, sunlight amount, and type of plant.

Multiple Choice

In an experiment, what is the term for the factors that you intentionally keep the same and do not change?

• Independent Variables

• Control Groups

• Dependent Variables

• Controlled Variables

Variables on a Graph

• Graphs visually show the relationship between variables.

• The independent variable is plotted on the horizontal x-axis.

• The dependent variable is plotted on the vertical y-axis.

Multiple Choice

On a graph that shows the results of an experiment, which axis is used to plot the dependent variable?

• It can be on either axis

• The x-axis

• Neither axis

• The y-axis

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Writing a Hypothesis

• A hypothesis is an educated prediction about an experiment's outcome.

• It is a testable explanation, not just a random guess.

• Use the ‘If... then...’ format to structure your hypothesis clearly.

• ‘If’ introduces the independent variable; ‘then’ predicts the dependent variable.

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Multiple Choice

When writing a proper hypothesis, what information should immediately follow the word 'If...'?

• Your prediction

• The dependent variable

• The independent variable

• The constants

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Common Misconceptions

Misconception	Correction
A hypothesis is just a wild guess.	A hypothesis is an educated guess based on research.
Control groups and constants are the same.	Constants are kept the same in all groups for a fair test.
Any factor that changes is a dependent variable.	The dependent variable is what is measured as the outcome.

Multiple Choice

Students want to test if changing the wing shape of a paper airplane will affect the distance it will fly. What is the dependent variable in this experiment?

• The type of paper used to construct the plane

• The distance the airplane will fly

• The temperature in the classroom

• The wing shape

Multiple Choice

Sam wants to see which cat food brand his cat, Misty, likes best. He puts out three different brands, giving one cup of each. He then records how much food Misty has eaten from each. What is the independent variable?

• The amount of cat food eaten

• Misty the cat

• One cup of cat food

• The brand of cat food

Multiple Choice

Based on the question 'What effect does studying have on your test grade?', which of the following is the best-written hypothesis?

• If I study for my test, then my test grade will improve.

• Good grades come from studying hard.

• If I study, then I will do well in school.

• If I get a good test grade, then I will study.

Multiple Choice

Carey and Justin are raising money (m) to purchase books (b) for their school's library. The more money they raise, the more books they can buy. Analyze this relationship to determine which variable is dependent on the other.

• The number of books (b) is the dependent variable.

• The amount of money (m) is the dependent variable.

• Both variables are dependent.

• Both variables are independent.

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Summary

• The independent variable is the one factor you intentionally change.

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

• Constants are all factors kept the same to ensure a fair test.

• A control group is used as a baseline for comparison.

• Graph the independent variable on the x-axis and the dependent on the y-axis.

• A hypothesis is a testable prediction, often using an "If..., then..." format.

Poll

On a scale of 1-4, how confident are you about identifying independent and dependent variables?

• 1

• 2

• 3

• 4