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FIND THE WASHER:

 SYNOPSIS

 PRINCIPAL CONCEPT

 ASSOCIATED CONCEPTS

1. Science is a way of obtaining information about the natural world.

2. New information may cause scientists to change their minds.

3. Scientific knowledge is tentative and uncertain.

ASSESSABLE OBJECTIVES

Students will.....

1. formulate a number of hypotheses and test their predictions.

2. recognize why scientific knowledge is tentative and uncertain.

3. use this exercise as an illustration of uncertainty in science.

 MATERIALS

One closable box with six crossed wires (see below) and 1-2 washers. A good example consists of a cigar box with 3 wires (A, B, and C) running lengthwise through the box, and 3 shorter wires (1, 2, and 3) running through the box across its width. Wires are made of straightened coat hanger wire, or equivalent. Tag the wires with the appropriate letter or number.

SAFETY TIP: Be sure to pad the cut ends of each wire to avoid injury. Use tape, glue drops, or shrink-tubing.

 TIME

 STUDENT HANDOUTS

 TEACHING STRATEGY

1. Before class, a washer is placed on a wire so that it slides between two wires or between a wire and the box side. The box is then closed and sealed with rubber band. The wire ends extend visibly beyond the box.

2. A diagram of the box is placed on the board or overhead with wires labeled.

PROCEDURES

 1. The general internal structure of the box is explained to the students (show diagram on overhead or board), and they are told that a washer has been placed on a wire somewhere inside.

2. Explain that the task for the class is to establish exactly where the washer is and to offer some evidence that they are correct.

3. Tell the students that only you (the teacher) can handle the box, but that you will do whatever they wish with the box (short of opening it), including the pulling out of the wires. Explain that the task is not completed until all the wires have been removed.

4. Remind students that you will only perform activities that reflect group consent and that all requests must be in the form of a hypothesis and a prediction.

5. As you do the activity, write each hypothesis and prediction on the board.

6. When all wires are removed, ask the students to determine/decide where the washer was and to cite the evidence they used to arrive at that conclusion. Entertain alternative solutions and evidence, and record these, too.

7. Open the box and show them the washer on the bottom of the box.

8. Have the students decide if their evidence is sufficient to establish where the washer was. Would another testing strategy have worked as well? Would another strategy have been more efficient (higher confidence, but with fewer moves)? What tests, if any, would have been more revealing?.

9. If there is sufficient interest from the class, and especially if there is not a consensus as to the original location of the washer, reset the washer in the box (in a different place!), and take the class through the process again.

 ASSESSMENT

 1. Ask the students to explain the Principal Concept or any of the Associated Concepts in their own words.

2. Given a mystery box with a washer in it, develop a hypothesis and prediction, and design a procedure to test them.

3. Why didn't opening the box after testing establish where the washer was?

EXTENSIONS

& VARIATIONS

 If later trials are used (that day, or another; it also makes a good "sponge" or fill-in activity for a shortened period, or some extra time at end of a period), you can increase the difficulty by:

a) placing the washer at a junction of two wires, so both wires pass through it, or

b) adding a second washer to another wire, or

c) adding the second washer to a junction of two wires.

 OTHER RESOURCES

 ATTRIBUTIONS

Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.

1. Original Source: unknown

2. Modified by: Tom Watts

3. Reviewed / Edited by: Martin Nickels, Craig Nelson, Jean Beard 2/5/97

4. Edited / Revised for website by L. Flammer 2/09/98