Identifying Variables and Constructing a Hypothesis

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Manipulating Variables In An Experiment

• Read the following two pages about experimental design and variables. Answer the questions below by typing in the box provided.– Science Buddies – Doing a Fair Test– True Experimental Design

• Using detail, describe why it is important to manipulate one variable at a time in an experiment.

• What variable will you be manipulating in your experiment?

Types of Variables• Variables are a key component of an experiment. Read the

following page to learn more about variables and to see examples of variables in experiments.

• Types of Variables

• Identify the variables in your experiment:– What is your independent variable?

– What is your dependent variable?

– Controlled variables are sometimes called constants. What are your controlled variables in your experiment?

– Assess the variables you will be testing using the checklist at the bottom of the variables webpage. Adjust your list as needed.

Types of Variables

• Controlled experiments are experiments which contain at least one control and at least one experimental group.

• The control group is the group used for comparison. Read about control groups on the following page.– Scientific controls

Types of Variables

• A research group wanted to know whether using green bags increased the shelf life of bananas. The group took a bunch of bananas and removed individual bananas from the bunch. Half of the bananas in the bunch were left on the counter for one week and the other half of the bananas were placed in green bags for one week. At the conclusion of the week the research team evaluated the ripeness of the bananas. What is the control group in this experiment? Why did you choose this group?

Types of Variables

• Navigate to the following website and identify the independent and dependent variables for the experiments. List the experimental and control group present in each experiment. Check your answers at the bottom of the page.

Constructing a Hypothesis• Click on the following two links and read the information provided.

– Constructing a hypothesis.– A strong hypothesis.

• Construct a testable hypothesis for the following observations.– A student notices that the water in the stream near the roadway is cloudier than

the water upstream in the forest.

– A student notices that sound seems to travel at different rates in water versus in the air. They complete some background research and realize that the speed of sound is related to density of the substance through which the sound waves travel.

• Read the information on this website to determine the difference between null and alternative hypotheses. – Null vs. Alternative Hypothesis.

Create a null and an alternative hypothesis for your experiment.

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