Writing a Hypothesis for Your Science Fair Project

What is a Hypothesis?

A hypothesis is the best answer to a question based on what is known. Scientists take that best answer and do experiments to see if it still makes sense or if a better answer can be made.

When a scientist has a question they want to answer, they research what is already known about the topic. Then, they come up with their best answer to the question based on what they know. This is called a hypothesis. The hypothesis has to be testable. A scientist must be able to do an experiment to test if the hypothesis is a good answer to the question.

The hypothesis also leads to predictions, which are guesses about what will happen in the experiments. These predictions usually have the pattern "If ____ then ____". The predictions include what the scientist will change in the experiment (called the independent variable) and what they will observe or measure (called the dependent variable). A hypothesis can have more than one prediction, but usually one or two predictions are enough for a science project.

Examples of Hypotheses and Predictions

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Question	Hypothesis	Prediction
Do larger dogs eat more food than smaller dogs?	Larger animals of the same species require more food to meet their energy needs compared to smaller animals of the same type.	If given the opportunity to eat as much as they want, then a 70-pound dog will eat more food than a 30-pound dog.
Does fertilizer help a plant grow bigger?	Adding fertilizer to the soil gives plants more of the nutrients they need to grow. With more nutrients, the plants will grow more.	If I fertilize some tomato seedlings but not others, then the seedlings that were fertilized will grow taller and have more leaves than the seedlings that were not fertilized.
If you increase the current, does an electric motor spin faster?	Increasing the current flowing through an electric motor's electromagnet increases the strength of the magnetic field. A stronger magnetic field will make the motor spin faster.	If I increase an electric motor's current, then the RPMs (revolutions per minute) of the motor will increase too.
Does a classroom get louder when the teacher is not in the room?	When the teacher leaves the classroom, students feel like they can talk more and louder. This makes the classroom louder.	If I measure the noise level in a classroom when a teacher is in the classroom and when the teacher is gone, then I will see that the noise level is higher when the teacher is gone.

What if My Hypothesis is Wrong?

What if your science project data does not match your predictions? Is it bad that your hypothesis is wrong? Don't worry! The goal of a science project is not to prove your hypothesis right or wrong. The goal is to learn more about how the natural world works. Even in a science fair, judges can be impressed by a project that started with a bad hypothesis. What matters is that you understood your project, did a good experiment, and have ideas for how to make it better.

In fact, scientists never say their hypothesis is, right or wrong. Instead, they say that their experiment supports or does not support their hypothesis. This is because nature is complex, so it takes more than one experiment to figure everything out. For example, let's say you make a hypothesis that earthworms can't survive in places with cold winters. You predict that you'll find earthworms in Florida, but not in Alaska. When you dig in both places, you find earthworms in Florida, but not in Alaska. Your data supports your hypothesis, but you can't be sure there are no earthworms in Alaska. After all, you only searched a very small amount of all the dirt in Alaska. That's why scientists say the data supports their hypothesis instead of saying it proves their hypothesis. And just so you know, there are earthworms in Alaska!

What Makes a Good Hypothesis?

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Hypothesis Checklist	For a Good Hypothesis, You Should Answer "Yes" to Every Question
Is the hypothesis based on information you found in books or other sources about the topic?	Yes / No
Can you make at least one clear prediction (guess) based on the hypothesis?	Yes / No
Can you test the predictions that come from the hypothesis in an experiment?	Yes / No
Does the prediction have something that you change (independent variable) and something that you observe or measure (dependent variable)?	Yes / No

Teacher Tool Box

Assign these with any LMS:

Hypothesis Quiz
My Science Project Hypothesis (Student Worksheet)

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