© 1999 ENSI (Evolution & the Nature of Science Institutes) www.indiana.edu/~ensiweb This material may be copied only for noncommercial classroom teaching purposes, and only if this source is clearly cited.

### FIND THE WASHER:

Modified By Tom Watts

THE NATURE OF SCIENCE

Basic Processes

Hypothesizing, Testing

#### SYNOPSIS

A closed box is shown to the class. It can be seen that 3 wires run through the box lengthwise and 3 more run through it widthwise, creating a grid of 6 crossed wires. The class is told that there is a metal washer somewhere on one or two of the wires inside the box. The challenge is to propose a series of "tests" (pulling out the wires, one at a time, listening for the washer to drop) in such a way that the washer's location can be ascertained.

#### PRINCIPAL CONCEPT

Scientific hypotheses are subject to being tested.

#### 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.

20-30 minutes

none

#### TEACHING STRATEGY

Before using any of our Nature of Science lessons, be sure to read our General Background Information, with our Rationale and our Approach, and tips for Presenting the lessons for maximum effect and Dispelling some of the popular myths about science.

In any of the discussions expected with the class, select a few key items (important concepts) that lend themselves to interpretation, and introduce class to the Think-Pair-Share (TPS) routine dealing with those items. This is how "Active Learning" is done.

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

ALTERNATIVES TO TRY:
1. See "Mystery Boxes" lesson

2. Check out "The Great Volume Exchanger" lesson for examples of discrepant events to analyze in a scientific way.

3. Try the Magic Hooey Stick lesson.

4. Do the "Phantom Tube" demo, as described in Teaching About Evolution and the Nature of Science. Unfortunately, this one doesn't work too well, so get the detailed instructions for making and demonstrating a Phantom Tube that works.. This is a Flinn's Chem Fax, a 4-page version of their puzzle tube. You pull on the strings and the students watch the other strings move up and down in surprising ways. You can walk through the entire process of science using the Phantom Tube - OR... decorate your Phantom Tube with mystical figures and present it with flourish as real "MAGIC" (see example at left) - then "reluctantly" let students get skeptical and critique that idea and seek a NATURAL explanation. MOST IMPORTANT: do NOT allow the students to see the inside of the tube, nor explain how it works, or even give cues. As in the Mystery Boxes, get students to use drawings to show their hypotheses (or models) of what they think the inner workings are most likely to be, and figure out ways to test those hypotheses. If anyone hits on the its essential mechanism, do NOT say "that's it!", Just ask "does it work?" If it does, it's the "Best Hypothesis so far." It's important for them to see that in science we never get to see the "answer." It's always tentative - the explanation that works best - so far. Click Here for Special Instructions.

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