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Wednesday, December 16, 2009

Mission Folder Tip: Testing a Hypothesis Through Experimentation

Once your teams have constructed an effective hypothesis, the next step in the scientific method is to test the hypothesis through experimentation. Here is a great opportunity to have your students start a science notebook, if they have not yet started recording their progress.



Steps to Identifying and Conducting an Appropriate Experiment to Test a Hypothesis

1.) Present Hypotheses
Make a list of all potential hypotheses to be tested.

2.) Make Predictions
For each hypothesis, ask what would be true if the hypothesis were true.

3.) Write the Experimental Procedure
The experimental procedure is a step-by-step recipe for the science experiment. A good procedure is complete and contains enough details that someone else could easily duplicate the experiment.

Once students have formed a hypothesis, guide them to develop their experimental procedure to test whether their hypothesis is true or false.

To view the key elements of the experimental procedure and an experimental procedure checklist, click here.

4.) Identify the Independent and Dependent Variables
The first step of designing the experimental procedure involves planning how to change the independent variable and how to measure the impact that this change has on the dependent variable.

To practice identifying the independent and dependent variables, click here.

To guarantee a fair test when conducting the experiment, make sure that the only thing changing is the independent variable. All controlled variables must remain constant.

5.) Design the Experiments
How can you help your teams identify an appropriate experiment that will effectively test their hypothesis? Begin by asking the students, “What can I do that will give me one result if my hypothesis is true, and a different result if my hypothesis is false?”

Design at least one possible experiment for each hypothesis. Be sure that each experiment tests only one hypothesis.

For each hypothesis in step 1, have your students make a list of things that would have to be true if the hypothesis were true. Using the predictions they made in step 2, design an experiment to test each of the hypotheses.

6.) Experimental Group vs. Control Group
Every good experiment compares different groups of trials with each other. Such a comparison helps insure that the changes you see when you change the independent variable are in fact caused by the independent variable. There are two types of trial groups: experimental groups and control groups.

The experimental group consists of the trials where you change the independent variable. For example, if your question asks whether fertilizer makes a plant grow bigger, then the experimental group consists of all trials in which the plants receive fertilizer.

In many experiments it is important to perform a trial with the independent variable at a special setting for comparison with the other trials. This trial is referred to as a control group. The control group consists of all those trials where you leave the independent variable in its natural state.

In another type of experiment, groups of trials are performed at different values of the independent variable. For example, if your question asks whether an electric motor turns faster if you increase the voltage, you might do an experimental group of three trials at 1.5 volts, another group of three trials at 2.0 volts, three trials at 2.5 volts and so on.

In such an experiment you are comparing the experimental groups to each other, rather than comparing them to a single control group. You must evaluate whether your experiment is more like the fertilizer example, which requires a special control group, or more like the motor example that does not.

7.) Repeat the Experiment
Repeating the science experiment several times is an important step to verify that your results are consistent and not just a coincidence.

For a typical experiment, students should plan to repeat the experiment at least three times. The more they test the experiment, the more valid their results will be.

If students are conducting an experiment that involves testing or surveying different groups, they will not need to repeat the experiment three times, but they will need to test or survey a sufficient number of participants to insure that the results are reliable.

For information on how to use a scientific survey as an experiment, click here.

8.) Preparing and Conducting an Experiment
a.) Instruct students to review their experimental procedure. Are all of the necessary steps written down? Do they have any questions about how to do any of the steps?
b.) Collect and organize all materials, supplies and equipment needed to do the experiment.
c.) Think ahead about safety! Are there any safety precautions the students should take? Will they need adult supervision? Will the students need to wear gloves or protective eye wear? Keep a fire extinguisher nearby, if applicable.
d.) Have the students record all of their observations during their experiments in the scientific notebook.
e.) Have the students prepare a data table so they can quickly write down their measurements as they observe them.
f.) Guide the students to follow their experimental procedure exactly. If the students need to make changes in the procedure, which often happens, they must write down the changes exactly as they make them.
g.) Remind students to be consistent, careful and accurate when taking measurements.
h.) If possible, have the students take pictures, drawings or videos of their experiments along the way; these will help the students explain what they did and enhance their Mission Folders.

For more tips or guidance on testing a hypothesis through experimentation, check out the the eCYBERMISSION webinar, Testing a Hypothesis Through Experimentation.

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