Overview

Students first examine their wind-ups closely to explore how they work, and analyze some mini-experiments to see what role each part plays. Next, there are some focusing questions that help develop concepts of energy. Finally, they write descriptions about how wind-ups work.

Advance Preparation

• Prepare chart for student observations of what makes a wind-up go.
• Photo copy the worksheet: “How a Wind-up Works”.
• Photo copy the assessment: “Energy Concepts”.
• Photo copy the experiment 2a, 2b and 2c worksheets if the experiments are to be done by groups, not by demonstration. (See procedure step 2, below.)

Materials

• Wind-ups already made by students
• Materials for making wind-ups, for spare parts and for doing experiments

Procedure

1.      Class meeting. Ask students what they have noticed about the way a wind-up works. Chart their observations. Here are some focusing questions that might help to structure the discussion:

• What changes happen when you wind up the stick?
• What would happen if you replaced the rubber band by a piece of string?

Students should be able to answer this question immediately, but you can provide a length of string to each group in case students want to try this experiment.

• When you let the stick go, what parts are turning, and what parts are not?

This is hard to answer without seeing inside the cup or tube. Provide a transparent plastic cup to each group in case students want to see for themselves. 

• What is making some parts turn?
• What is keeping other parts from turning?

2.      Wind-up Experiments. Here are three simple demonstrations that you can use as demonstrations, or the students can do in groups, to reveal more about how wind-ups work. As a student experiment, give one of the three experiments (2a, 2b, or 2c) to each group.

a)      Put a stick on each side, instead of just on one side. (See movie on Experiment A)

• What happens?
• Why doesn’t it work?
• When the rubber band unwinds, what does it need to do, in order to make the wind-up go?

b)      Remove the second stick, so you are back to your original wind-up, with only one stick. Make the stick shorter (by breaking it) so it can’t touch the floor or table. (See movie on Experiment B)

• What happens now?
• What does the stick have to do to allow the wind-up to go?
• Why does the stick need to touch the floor?

c)      Replace the broken stick with a new stick that can touch the ground, so you have your original wind-up. On the side with the paper clip, slip the rubber band through a bead, to keep the paper clip away from the wheel. (See movie on Experiment C)

• What do you notice about the paper clip?
• What does the paper clip need to do to make the wind-up work?
• What’s preventing the paper clip from doing its job?

3.      Class meeting. The class then meets to piece together the information from these experiments. Help them break down the entire sequence of steps that occurs between windup up the stick, and the wind-up traveling on its own. What is the job of each part? Make sure everyone understands this essential cause - effect reasoning. (See "Explaining the Wind-up Experiments.")

Review the energy concepts introduced in earlier lessons.. After it’s wound up, but before it is released, potential energy is what makes the wind-up “want” to go. The kind of potential energy is called elastic, which means that it is contained in something “springy” that is stretched or twisted, but would “like” to go back to its original shape. After the wind-up is released and moving across the floor, it has kinetic energy, which is the energy of motion. (Here is a movie on How  Wind-ups Work  and a more detailed discussion of energy transformations.) Some focusing questions about energy are:

• Where does the energy come from that’s needed to wind it up?
• Where do you get energy from?
• What energy changes take place as you wind it up?
• What happens to the energy when you let it go?
• What happens to the energy of the wind-up as it slows down and stops?

It may appear that energy is lost as the wind-up slows. However energy is always conserved.  The kinetic energy that appears to have been lost was converted to heat energy by that enemy of motion: friction.

Assessments. "How a Wind-up Works" can be given at the end of the period. It reveals student understanding of the energy inputs, outputs, and transformations in wind-ups. "Energy Assessments" distinguishes between potential and kinetic energy.

Homework or extension activity: Conduct a scavenger hunt at home or in the classroom for elastic-powered devices. Example include anything with a return spring that makes it come back to its original shape when you let it go: keyboard keys, door knobs, wind-up toys, snack food clips, clothespins, bulldog clips, tweezers, salad tongs, automatic door closers, staplers, push button switches (for example on a computer mouse), etc.

Outcomes

• Students look at a wind-up closely to uncover its principles of operation.
• Students use the results of simple experiments to draw conclusions about how a wind-up works.
• Students develop a series of cause-and-effect relationships linked together in a causal chain.
• Students develop concepts of potential and kinetic energy, and see how one is transformed into the other, using wind-ups as examples.

Worksheets for Experiments

Assessments