Hypothesis

Hypothesis

Middle School

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Learning Objectives

• Define a hypothesis and its purpose in a scientific investigation.

• Differentiate between independent, dependent, and controlled variables.

• Identify the key components of a testable hypothesis.

• Construct a hypothesis using the 'If... then... because...' format.

Key Vocabulary

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Hypothesis

A testable prediction about an experiment's outcome, often written as an "If...then..." statement.

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Independent Variable

The one factor a scientist intentionally changes in an experiment to observe its effects.

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Dependent Variable

The factor that is measured in an experiment to see how it is affected by changes.

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Controlled Variable

A factor that is kept the same throughout an experiment to ensure the test is fair.

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What Is a Hypothesis?

• A hypothesis is an educated guess or a prediction about your experiment.

• ​It is a testable explanation for a scientific question you are asking.

• It’s based on observations, research, and what you already know.

• It provides a clear direction for the experiment you will be conducting.

Multiple Choice

Which of the following best describes a hypothesis?

• A final, proven fact.

• A list of materials needed for an experiment.

• A testable prediction or educated guess about an experiment's outcome.

• The conclusion written after an experiment is finished.

Writing a Strong Hypothesis

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The 'If' Statement

• ​The 'If' part introduces the independent variable in your experiment.

• ​​This is the one factor that you are going to change.

• ​It clearly states the condition that you will be testing.

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The 'Then' Statement

• ​The 'Then' part introduces the dependent variable of the experiment.

• ​​This is the factor you will observe and measure for changes.

• ​It predicts the outcome that you expect to see happen.

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The 'Because' Statement

• ​The 'Because' part explains the reasoning for your scientific prediction.

• ​​It states why you think the change will cause that effect.

• ​This explanation should be based on your initial research or knowledge.

Multiple Choice

In the 'If... then... because...' structure of a hypothesis, what does the 'Then...' part introduce?

• The independent variable.

• The controlled variables.

• The reason for the prediction.

• The dependent variable.

Understanding Variables

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Independent Variable

• ​This is the one factor that you purposely change in an experiment.

• ​​Limiting this to one factor allows you to see its direct effect.

• ​For example, changing the amount of sunlight a plant receives.

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Dependent Variable

• ​This is the factor that you measure or observe to see results.

• ​​Its outcome depends on the change made to the independent variable.

• ​For example, you would measure the growth of the plant.

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Controlled Variables

• ​These are all other factors that must be kept constant and unchanging.

• ​​This ensures that the experiment is a fair and valid test.

• ​For example, using the same pot, soil, and amount of water.

Multiple Choice

An experiment is performed on plants to see how different liquids affect plant growth. Each plant gets the same amount of soil and sunlight. What is the role of the soil and sunlight?

• They are the dependent variables.

• They are the independent variables.

• They are the controlled variables.

• They are the hypothesis.

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Common Misconceptions

Misconception	Correction
A hypothesis is just a random guess.	It is an educated guess based on observation and prior knowledge.
You can test multiple things at once.	A fair scientific test should only have one independent variable.
If your hypothesis is wrong, the experiment is a failure.	A disproven hypothesis helps scientists eliminate possibilities and create new ideas.

Multiple Choice

To investigate how the temperature of a room impacts a plant's growth, a student sets up an experiment. What is the independent variable in this study?

• The type of plant used.

• The amount of light the plant receives.

• The plant's growth.

• The temperature of the room.

Multiple Choice

Which of the following is a correctly written hypothesis for the question: "How does the amount of fertilizer affect the height of a plant?"

• If a plant gets more fertilizer, then it will grow taller, because fertilizer provides essential nutrients.

• If a plant grows taller, then it must have received fertilizer.

• Fertilizer makes plants grow taller.

• More fertilizer and taller plants are related.

Multiple Choice

An experiment is set up to see how the mass of a ball affects the distance it rolls off a ramp. Why is it crucial for the scientist to use the same ramp and release the ball from the same height for each trial?

• Because the mass of the ball depends on the height of the ramp.

• Because the ramp and height are the dependent variables being measured.

• Because the ramp and height are controlled variables that could also affect the rolling distance.

• Because changing the ramp or height would make the experiment go faster.

Multiple Choice

A student hypothesizes: "If a tennis ball is frozen, then it will not bounce as high as a room-temperature ball because freezing makes the rubber less flexible." After testing, the frozen ball actually bounced higher. What is the most logical next step?

• Form a new hypothesis, possibly considering that freezing increases the ball's internal pressure.

• Change the data to match the original hypothesis.

• Repeat the experiment using a different type of ball.

• Conclude that the experiment was flawed and should be ignored.

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Summary

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

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

• The dependent variable is what you measure to see the effect of the change.

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

Poll

On a scale of 1-4, how confident are you about writing a proper hypothesis for an experiment?

• 1

• 2

• 3

• 4