## Overview

Students carry out the experiment on the effect of wheel size. They measure how far the large and small wheel wind-ups go. The students compare results, then discuss if this was a fair experiment.

## Materials

• Student wind-ups with lids as wheels from Lesson 4
• Student wind-ups with 6” paper saucers as wheels from Lesson 6
• Materials to repair wind-ups

• Photo copy the experiment worksheets: “Experiment: Wind-ups with Different Sized Wheels.”
• Determine the spaces where students will be able to test their wind-ups. Consider using the hall way in addition to the classroom, or even a lunch room

## Procedure

1.      Class meeting. The purpose of the meeting is to quickly review the experiment students will do and how they will do it..

Assign groups to particular areas, each with a “runway” of at least 15 feet. . Each student in the group will wind up and release his or her own wind-up. Students take turns helping with the measurement of the distance each wind-up goes. Remind students to be careful of the work of other groups.

Distribute the data sheets for comparing the two wind-ups. Discuss how students will measure the distances, and where they will record their data. Point out that they can try each wind-up two times and record the data for each trial.  Suggest that students wind their wind-ups at least 20 times.

2.      Students experiment with wind-ups.  Circulate among the groups, assisting with troubleshooting when wind-ups don’t work. Observe how students are making measurements and recording data, and ask questions about these procedures.

3.      Class meeting. The purposes of the meeting are for students to share data and look for patterns in it, and to see what variable was not controlled.

First ask students if there were any differences in how far the smaller and larger wheeled wind-ups went. Then collect and record data from about five students on a class chart. Encourage a variety of results by asking students: Who got different results from these?  With representative results to examine, ask students to look for patterns in the numbers.  The typical generalization is: the bigger wheels went further than the smaller.  However there is a lot of difference among the results.

Ask students why they think there were such differences in distance traveled among wind-ups with large wheels (or smaller wheels). Reasons may include friction in the wind-up, rough spots in the floor, or wobbles in the wind-up or curves in its path.  However the most important uncontrolled variable is probably the number of times they wound the rubber band.  Ask students:

• How many times did you wind the rubber band?  Who wound their wind-up the most, who wound their wind-up the least? How far did they go?
• Is this a fair experiment about wheel size if we compare wind-ups which have different amounts of energy stored in their rubber bands?

Discuss the need for a fair experiment. The next experiment will repeat this experiment.  It will compare the same two wind-ups, but this time the experiment will control the number of times to wind the rubber band. This will be a fair experiment.

4.      Outcomes

• Students experiment with wind-ups having different sized wheels and collect data on how far they go.
• Students look for patterns in the data and generalize that the wind-ups with larger wheels seem to go further than those with smaller wheels.
• Students analyze the experiment to see if it was a fair experiment.  They look for what might make it unfair, such as differences in how many times they wound each wind-up.