In both comparative and experimental investigations, a hypothesis should be established. A hypothesis is a proposed explanation for an observable phenomenon. For a hypothesis to be used in science, one must be able to test it through an experiment. The hypothesis is not just an "educated guess." Hypotheses should be based on previous observations that cannot be explained with available information. An experiment is designed to test the hypothesis.

A hypothesis is supposed to address causes (independent variable) that lead to effects (dependent variable). The suggested cause is the independent variable; the expected effect or result is the dependent variable and is a prediction of what the scientist thinks will happen.

The basic form of a hypothesis is usually similar to one of the following:

1. IF independent variable is applied, THEN the dependent variable will happen.
2. AS the independent variable changes, THE dependent variable changes.

An easy way to write a hypothesis is to take the independent variable and add a verb and then write the dependent variable and add a verb. For example, let's say that you were asked to write a hypothesis to answer the question "How does the amount of fertilizer affect plant growth?" First, you would need to determine the independent and dependent variable.

Independent variable:

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Amount of fertilizer

Dependent variable:

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Plant growth

Now that we have identified the independent and dependent variable, we can write our hypothesis. Click below to see the hypothesis form.

Let's try another. Read the following scenario.

A NASA engineer wants to see if salt will reduce the amount of ice and snow buildup on the runway. She spreads 200 lbs of salt on a test runway and simulates an airplane landing by using test equipment. She then repeats the test on a runway with 100 lbs and then without applying any salt.

Identify the independent and dependent variable.

Independent variable:

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Salt

Dependent variable:

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Amount of ice and snow on the runway

Watch the video and read the scenario to create a hypothesis for this experiment.

Source: The Extreme Diet Coke & Mentos Experiments, Zorro103, Youtube

Mixing large chewy mint candies with a carbonated drink such as diet cola will produce a fountain of soda that spews from the bottle. You decide to do an experiment using diet cola and different types of large chewy candies. You decide to use a diet soda instead of a regular soda so that your clean-up is easier; it won't have the sugary, sticky residue that comes from regular sodas. Below is the procedure that was followed and the observations that were made.

1. Obtain mint and fruit-flavored large chewy candies.
2. Examine both types of large chewy candies under a stereoscope.
3. Draw a picture of what you see.
4. Obtain two bottles of diet cola, both need to be the same size.
5. Place one large chewy mint candy into the diet cola.
6. Place one large chewy fruit candy into the other diet cola.

In your observations about the large chewy mint candies, you notice that there are small pits all over the surface of the large chewy mint candies, but the large chewy fruit candies have a smooth coating on them. In your observations, you write that the diet cola with the large chewy mint candies looked like a geyser as the diet cola was streaming from the bottle. You note that the diet cola with the large chewy fruit candy remained intact and unchanged.

What is the independent variable (the part of the experiment that you changed) in this experiment?

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The type of large chewy candies

What is the dependent variable (the part that you measure because of the independent variable) in this experiment?

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The height that the soda will spew from the bottle

Write a testable hypothesis in your notes for the scenario above.