What is a Hypothesis?

How does a hypothesis begin?

What do you do with it?

How do you make one?

Making a hypothesis is a step in the Scientific

MethodThe 7 basic steps of the scientific method:

1. Asking a question2. Completing research3. Making a hypothesis4. Planning an investigation5. Recording and analyzing data6. Explaining the data7. Communicating the results

How does a hypothesis begin?

Scientists make lots of observations. This leads them to form scientific questions about what they have observed. Each scientist creates an explanation – or hypothesis – that he or she thinks will answer the question.

A scientist bases his/her hypothesis both on what he or she has observed, and on what he or she already knows to be true.

• In science a prediction is an educated guess about the expected outcome of a specific test. In science a hypothesis goes further.

• A hypothesis includes a possible explanation about why the expected outcome of a test will occur

A hypotheses is not just a prediction!

What do you do with a hypothesis?

The hypothesis that a scientist creates leads him or her to make a prediction that can be tested next in an investigation.

• It does not matter if your experiment has been done a thousand times before!

• What matters is that you don't know the results and that you can independently find a verifiable answer.What does verifiable mean?

It means capable of being tested (verified or falsified)

by experiment or observation.

How do you write a hypothesis?

A good hypothesis includes two parts: 1. a prediction about the outcome of a

scientific investigation

----and----

2. an explanation for why those results will occur

Prediction vs. Hypothesis

Usually, a hypothesis is based on some previous observation

Example Prediction: If it gets cold outside then leaves will change colors.

Are these two events connected? How?

Example Hypothesis:If it gets cold outside then the leaves will change color because leaf color change is related to temperature.

How do you write a hypothesis?

• Chocolate may cause pimples. • Salt in soil may affect plant growth. • Plant growth may be affected by the color of the

light. • Bacterial growth may be affected by temperature. • Ultra violet light may cause skin cancer. • Temperature may cause leaves to change color.

Do you think that these statements make good hypotheses?

Why or why not?

The word “may” does not suggest how we would prove these statements

• Chocolate may cause pimples. • Salt in soil may affect plant growth. • Plant growth may be affected by the color of the

light. • Bacterial growth may be affected by temperature. • Ultra violet light may cause skin cancer. • Temperature may cause leaves to change color.

How do you write a hypothesis?

How do you write a hypothesis?

A hypothesis is worded as a prediction about what will happen if you change something and is worded like this:

If … then… because…Example: If students eat a lot of candy then

they will get more cavities because sugar on teeth causes cavities.

http://iqa.evergreenps.org/science/games/elephant.mpeg

Example question

Lets say you notice that the tomato plant closest to the fence in your neighbor’s yard is much taller than any of the other plants in her garden bed. You also notice that the neighbor turns on her sprinkler system every day, and that some of this water reaches only her big plant.

You create a question: Does daily watering from a sprinkler make a

tomato plant grow faster than other tomato plants?

Example hypothesis Now you can create a hypothesis to address

your question:

“If tomato plants in a garden are watered daily then they will grow faster because tomato plants grow more when they get more water.”

Notice how the hypothesis makes a prediction that can be tested

If….then….because….

After the word “If ”… explain what will change in the investigation

After the word “then ” …write what you predict will happen as a result of that change

After the word “because” …explain why you think the result will happen

Testing a HypothesisThe hypothesis must be worded so that it can be tested in your experiment.

• Do this by expressing the hypothesis using an independent variable (the variable you change during your experiment) and a dependent variable (the variable you observe changes in). The dependent variable depends on changes in the independent variable).

• In fact, many hypotheses are stated exactly like this:

" If a particular independent variable is changed, then there is a change in a certain dependent variable, because of why you think the result will happen “

Variables in HypothesesIf… then… because

• If people are exposed to high amounts of ultraviolet light, then they will have a higher frequency of skin cancer because ultraviolet light causes skin cancer

• If leaves are exposed to low temperatures, then the leaves will change color because the plant stops making chlorophyll

DEPENDENTVARIABLE

The variable that you observe and measure the results

INDEPENDENT

VARIABLEThe variable that

you control and

change

Original:Ultra violet light may cause skin cancer. • If… then…because• If people are exposed to high amounts of ultraviolet

light, then they will have a higher frequency of skin cancer because ultraviolet light causes skin cancer

Original:Temperature may cause leaves to change color. • If… then…because• If leaves are exposed to low temperatures, then

the leaves will change color because the plant stops making chlorophyll

If….then….because…. Practice

Your Turn to Practice

Rewrite the following hypothesis as an If… then…because statement.• What is the dependent variable?• What is the independent variable?

Chocolate may cause pimples. Rewritten Hypothesis:

dependent variable:

independent variable:

Chocolate may cause pimples.

Rewritten hypothesis:If I eat chocolate, then I will get pimples because chocolate causes my skin to produce excess oil which clogs the pores of my skin

Did your Hypothesis look something like this?

Rewrite the following hypothesis as an If… then…because statement.• What is the dependent variable?• What is the independent variable?

Salt in soil may affect plant growth. Rewritten Hypothesis:

dependent variable:

independent variable:

Your Turn to Practice

Did your Hypothesis look something like this?

Salt in soil may affect plant growth.

Rewritten hypothesis:If salt is added to the soil, then the growth of the plant will be affected because salt prevents the plant from absorbing the water

Rewrite the following hypothesis as an If… then…because statement.• What is the dependent variable?• What is the independent variable?

Plant growth may be affected by the color of the light. Rewritten Hypothesis:

dependent variable:

independent variable:

Your Turn to Practice

Did your Hypothesis look something like this?

Plant growth may be affected by the color of the light.

Rewritten hypothesis:If the color of light is changed, then plant growth will be affected because plants prefer different colors of light!

Rewrite the following hypothesis as an If… then…because statement.• What is the dependent variable?• What is the independent variable?

Bacterial growth may be affected by temperature. Rewritten Hypothesis:

dependent variable:

independent variable:

Your Turn to Practice

Did your Hypothesis look something like this?

Bacterial growth may be affected by temperature.

Rewritten hypothesis:If the temperature is increased, then bacteria will grow faster because those little buggers like it hot!

Summary – Hypothesis Writing Tips

1. The question comes first. Before you make a hypothesis, you have to clearly identify the question you are interested in studying.2. A hypothesis is a statement, not a question. Your hypothesis is not the scientific question. The hypothesis is an educated, testable prediction about what will happen.3. Make it clear. A good hypothesis is written in clear and simple language. Reading your hypothesis should tell someone exactly what you thought was going to happen when you started your experiment.4. Keep the variables in mind. A good hypothesis defines the variables in easy-to-measure terms, like who the participants are, what changes during the testing, and what the effect of the changes will be.5. Make sure your hypothesis is "testable." To prove or disprove your hypothesis, you need to be able to do an experiment and take measurements or make observations to see how two things (your variables) are related. You should also be able to repeat your experiment over and over again, if necessary.6. Do your research. You may find many studies similar to yours have already been conducted. What you learn from available research and data can help you shape your experiment and hypothesis.7. Don't bite off more than you can chew! Answering some scientific questions can involve more than one experiment, each with its own hypothesis. Make sure your hypothesis is a specific statement relating to a single experiment.