# Investigation: Design Experiment

Once students formulate a hypothesis for their investigation, they must design a procedure to test it. A well-designed investigation contains procedures that take into account all of the factors that could impact the results of the investigation. These factors are called variables.

NOTE: at elementary level, you may wish to begin by using the phrases “What is changed,” “What stays the same,” and “What is measured.” Once students are comfortable with these ideas and that of controlling the experiment, the term variable can be introduced. Young students can often get hung up on the differences among the terms, which can hamper the investigation.

There are three types of variables to consider when designing the investigation procedure.

• The independent variable is the one variable the investigator chooses to change.
• Controlled variables are variables that are kept the same each time.
• The dependent variable is the variable that changes as a result of /or in response to the independent variable.

Having students talk through the investigation will help them to clarify the different variables involved in the experimental design. What factors will change? What factors will stay the same? The challenge is for students to create what is called a “fair test.” In a fair test, only one factor or variable is changed at one time so that the investigator can determine if the changed factor has an impact on the end results.

One of the easiest ways to help students understand the concept of a fair test is to give them an example that is NOT a fair test. For instance, suppose the problem is to determine which stain remover is best at removing stains. It would not be fair to test one stain remover on a well set grass stain while testing the other stain remover on fabric only lightly soiled with dirt—a much easier stain to remove. A well designed procedure avoids such unfair comparisons.

Another hands-on way to introduce a fair test is to ask students, “Who can make the best paper airplane?” Once two students are selected to compete, hand one a large piece of construction paper and the other a piece of regular copy paper. Students will immediately note that this is “unfair.” If we want the test to be fair, only the paper airplane design can be different. Everything else, including how hard the airplane is tossed, must be the same.

Following the steps listed below will help students as they develop an investigative procedure.

## Step A – Clarify Variable

Clarify the variables involved in the investigation by developing a table such as the one below.

Testable Question What is changed? (independent variable) What stays the same? (controlled variables) Data Collected (dependent variable)
What detergent removes stains the best? Type of detergent, type of stain Type of cloth, physical process of stain removal Stain fading over time for combinations of detergents and stains

## Step B – List Materials

Make a list of materials that will be used in the investigation.

Stain Removal Investigation Materials

• 100% cotton cloth samples
• Ketchup
• Coffee
• Ink
• Grass
• Soil
• Commercial detergent #1
• Commercial detergent #2
• Vinegar
• Vinegar and baking soda mixture
• Water
• Soap
• Wash basin
• Timer/stopwatch
• Rubber gloves

## Step C – List Steps

List the steps needed to carry out the investigation.

Stain Remover Investigation Procedure

1. Place a ketchup stain approximately 4 inches in diameter on 100% cotton fabric. Prepare 4 identical stain samples in addition to the first sample. Label the samples (vinegar, vinegar and baking soda mixture, commercial detergent #1, commercial detergent #2)
2. Place 10mL of stain remover on the ketchup stain sample. Wait 3 minutes. Scrub for 1 minute. Repeat with each of 4 stain removers. (vinegar, vinegar and baking soda mixture, commercial detergent #1, commercial detergent #2)
3. On the fifth sample, do not put on any stain remover. Leave the ketchup stain as is. Scrub for 1 minute. Use permanent marker to write the word ketchup on each sample.
4. Wash each sample using soap and water in a basin.
5. Compare the samples to see which stain remover worked the best.
6. Repeat the experiment using different stains (coffee, ink, grass, and soil)

## Step D – Estimate Time

Estimate the time it will take to complete the investigation. Will the data be gathered in one sitting or over the course of several weeks?

## Step E – Check Work

Check the work. Ask someone else to read the procedure to make sure the steps are clear. Are there any steps missing? Double check the materials list to be sure all to the necessary materials are included.