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Lesson Plans
Designing Experiments
Overview Procedures for Teachers Organizers for Students


Procedures for teachers is divided into three sections:
Prep -- Preparing for the lesson
Steps -- Conducting the lesson
Extensions -- Additional activities


Prep

Media Components

Computer Resources:
  • Modem: 56.6 Kbps or faster.
  • Browser: Netscape Navigator 4.0 or above or Internet Explorer 4.0 or above.
  • Macintosh computer: System 8.1 or above and at least 32 MB of RAM.
  • Personal computer (Pentium II 350 MHz or Celeron 600 MHz) running Windows® 95 or higher and at least 32 MB of RAM
  • RealPlayer plug-in. Download for free at www.real.com.
Specific Software Needed:
  • PowerPoint (optional)

Materials:

Students need the following supplies:

  • 4-5 pencils, preferably unsharpened
  • 3-4 planks or cardboard or other material that at least a two feet long and wide enough to roll a pencil along
  • 4-5 yard sticks
  • chalk (this will be used to roll the pencils down)
  • 2 pairs of same-size running shoes (optional)
  • chart paper and markers

Bookmarked sites:

Scientific method/variables Web sites Technology Web sites
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Steps

Introductory Activity:

  • Share the following scenario with your students: A runner has two pairs of running shoes. To find out which pair will allow her to run faster, she puts on the first pair and runs around the track once in exactly 2 minutes. She puts on the second pair and runs around the track again, this time, making it in 2 minutes and 10 seconds. She decides the first pair is better, and heads to the store to return the second pair. Ask students:
    • What is the runner trying to test? That is, what question is she trying to answer?

    • Do you think her experiment can answer the question she is trying to answer? Why or why not?

    • Do you think both pairs of sneakers are treated fairly in the experiment or does one have better chances than the other? Why or why not?

    • Are there any factors that might have interfered with her experiment? If so, what are they? (e.g., what if she is winded from running around the track the second time?)

    • What did the runner assume when she designed this experiment? (Answer: that the type of shoes she was wearing would create a difference one way or the other.) Note: If students can’t come up with an answer for this question, have them think about it for homework. They will revisit it in the next activity.
  • Record students’ answers on a piece of chart paper. Tell them that in following activities, they are going to use what they learn to design a better experiment for the runner.

    Learning Activities:

    Activity 1

    Part one-independent, controlled, and dependent variables

  • Ask students to brainstorm what the following terms mean: independent variable, dependent variable, extraneous variables, controlled variables, and control group.

  • Then, write these simple definitions on the board:
    • Independent variable: the variable that is purposefully changed in an experiment
    • Controlled variables: the variables that are kept the same during an experiment
    • Dependent variable: the variable that is changed depending on the value of the independent variable
    • Extraneous variables: variables that are not or cannot be controlled that could interfere with an experiment
    • Control group: a group in which everything is the same as the test group except that the independent variable stays the same
    You may want to print out a copy of the following Web page to further explain these concepts:
  • Tell students they can begin to understand these terms by thinking back to the runner scenario. Break students into pairs and have them discuss and answer the following questions. (Go to STUDENT ORGANIZER: ACTIVITY ONE-PART ONE for a printer-friendly version of the following questions that doesn’t contain answers.)
    • Which variable changed (independent variable) in this experiment? (the running shoes the runner was wearing)

    • What were some of the controlled variables that should have stayed the same? (her energy level, the distance she ran)

    • Did all the controlled variables actually stay the same? (e.g., energy level) If not, how could they affect the experiment? (she may have been more tired the second time around, the wind may have picked up, she may not have tied the second pair as tightly as the first, etc.)

    • Was there a control group in the experiment? If so, what was it? If not, should there have been one? Why or why not?

    • What was the dependent variable in this experiment supposed to be? (the length of time it took the woman to run around the track)

    • In a successful experiment, the dependent variable must change based on changes in the independent variable. Is this the case with the runner’s experiment? Did the dependent variable (the time it took the woman to run around the track) change based solely on the independent variable (the shoes the woman was wearing), or were other variables possibly involved?

    • Based on what you know, was the runner’s experiment successful? Do you think she made a good decision about which shoes to keep? Why or why not?

  • Bring students back together to discuss the answers to the questions above. Record a list of what the dependent, independent, extraneous, and controlled variables were in the experiment.

  • HOMEWORK: Read through the STUDENT ORGANIZER-ACTIVITY ONE HOMEWORK assignment with students to make sure they understand it.

    Part two-control groups

  • Remind students about the runner scenario from part one of this activity. Ask about the existence of a control group. There wasn’t one in the runner’s experiment, but there probably should have been. If students have trouble understanding the concept of control groups, use the following anecdote to help them understand:
    Imagine that the runner’s experiment wasn’t flawed. Instead, the runner had controlled all of the variables in her running experiment. Every time she wore the first pair of sneakers, she ran around the track in 2 minutes. Each time she ran around the track in the second pair of sneakers, she ran around the track in 2 minutes and 10 seconds. Happy with what she thought were such decisive findings, she bought the first pair of shoes. What assumption did she make?

  • If students have difficulty coming up with the answer, tell them: The woman is assuming that whichever running shoes she is wearing will actually make a difference in her running speed. The woman’s running speed may vary + or -10 seconds no matter what. Or, her speed could vary independently of the shoes she wears, so the type of shoes she was wearing may not have made any difference in her running speed.

  • Ask students: Did the runner’s assumption affect the way she designed her experiment? How? (Because she is assuming that the type of shoes she is wearing will make a difference, she is attributing any difference in her running speed to the shoes.) Tell students that this type of assumption, based on personal opinion, is called a bias, and that one of the greatest challenges scientists face is trying to identify these biases in their experiment designs.

  • Break students into pairs. Ask them to discuss the following question: How could the runner design an experiment to avoid this design bias? In other words, how can she be sure that running shoes actually affect running speed, and that wearing one pair or another will impact your pace? (One way is by using a control group.)

  • Reconvene as a group and record students’ ideas on the board.

    Part three—designing a better experiment

  • Break students into small groups and ask them to design an experiment for the runner that would help her make a sounder decision regarding the sneakers. Remind them that to do this, they’ll need to eliminate all the variables except the running shoe variable. Tell them to use STUDENT ORGANIZER: ACTIVITY ONE-PART THREE to help design their experiment.

  • Group by group, have students share their revised experiments with the class. For each experiment, analyze whether all but the running shoe variable were controlled.

  • If the students missed the idea of repetition as a way to gather reliable data in their responses, you may want to share the following example:
    Your parent or guardian asks you to time your walk to school—he or she wants it to be as accurate as possible. If you time it only once, your estimate may not be representative. Maybe you were tired that day, and walked slower than usual. Maybe it was hot out, and you crossed the street a few times to stay in the shade, adding to the length of your walk. Maybe you were late so you ended up running. But, if you time yourself several days in a row, the differences caused by some of these circumstances start to even out. On the first day you walk slower than usual, and it takes you 15 minutes. The second day you’re really late, so you run and it takes you 10 minutes. The third day, you walk at a regular pace, and arrive after 13 minutes. If you average your results, they will be more accurate than if you just take one measurement.

  • If possible, choose the experiment design that seemed the soundest, or combine elements from the different experiments that seemed effective to create an experiment design that all of the students are happy with.

  • Then, have the students use two pairs of running shoes to try the experiment. They don’t both have to be new pairs—one could be new, one could be old. Have students compare the actual results with the results they had expected.

    Activity 2

  • Now, tell the students that they’re going to conduct an experiment to learn more about the role of independent, dependent, extraneous, and controlled variables in scientific experiments.

  • Pose the following question to the students: If you roll a pencil from an incline, will it roll twice as far as a pencil rolled from half as high up the incline? For example, if you roll a pencil from 2 feet up an incline, will it roll twice as far as a pencil rolled from one foot up the incline?

  • Break students into groups of three to four. Give each group STUDENT ORGANIZER-ACTIVITY TWO. Ask them to complete all sections of this sheet.

    Note to teachers: You may want to have students assume specific roles within their groups: data recorders (to take measurements and record the data), variable controllers (to make sure that each repetition of the experiment is consistent and avoids the pitfalls discussed earlier), and engineers (to set up the plank, roll the pencil).

  • After conducting the experiment, ask students to discuss the data and analysis they recorded on their STUDENT ORGANIZER-ACTIVITY TWO handout.

  • As a class, ask students to generate a list of designing and experimenting Do’s and Don’ts. Record their list on a piece of chart paper and display in the classroom.

    Culminating Activity/Assessment:

    For the final activity of this lesson, student will share what they’ve learned with another classroom. They can do this by creating a one-hour, student-led workshop for another class in their school, or create a Web page that shares what they’ve learned. Their presentation or Web page should include the following:
    • Definitions of the terms “independent”, “dependent”, “controlled”, and “extraneous variables”, and “control group”.
    • An explanation of why these terms are important in a scientific experiment, along with examples that illustrate their points.
    • A practical list of Do’s and Don’ts of experiment design.
    • An activity that will help another class understand the new concepts.
    Note to teachers: Use the following Web sites for information on how to create a PowerPoint presentation or Web page:
    Extensions

    Cross-Curricular Extension: History
    Have students go to the interactive Web site listed below to learn how yellow fever was cured. After reading through the site, have students analyze the events in terms of the scientific method. Have them determine what the question the scientists were trying to answer, the method they used to uncover the truth (including the dependent, independent, controlled, and extraneous variables—they will have to infer what these were) and what the results of the experiment were.



    Overview | Procedures for Teachers | Organizers for Students