## Overview

Students revisit the sled that won’t go down the ramp, and invent a new way to “help” it move by putting rollers under it.

• Copy worksheet "How did I get it to roll?"  (Download below)

## Materials

• Ramps and stands, one per pair of students; attach a surface (the surface used in Lesson 4 that had the most friction, such as felt or sandpaper).
• Redesigned sleds from Lesson 5
• Plain cardboard sleds
• Wooden skewers, straws, stirrers, pencils, crayons, paper clips, paper fasteners, masking tape

## Procedure

1.      Review of the sled problem: Set up a ramp per pair of students; make sure the sled cannot initially slide down, due to the combination of surface and slope. Students may use plain cardboard sleds or the sleds they redesigned in Lesson 5. Review what happened when the surface was too rough and/or the slop wasn’t steep enough to make the sled move on its own:

• What is happening here? Use the word “friction to describe what is holding the sled back.
• Why doesn’t the sled want to go down?

2.      A new way to get it to move. Provide skewers, straws, stirrers, pencils, crayons, paper clips, paper fasteners, masking tape. Ask:

• How could you use these to help the sled move down the ramp?

Provide time for students to experiment with the materials. Some students will probably come up with the idea of placing straws, skewers, crayons or stirrers under a sled, to allow it to roll down. If not, help by asking:

• What would happen if I put this (indicating a straw) under the sled?
• Which of these would work to help the sled go down?

3.      Class meeting: Lead a discussion of the methods students used, and which ones worked. Introduce the words roll and roller.

4.      Further experimenting and recording results: If students haven’t all tried rollers, provide time for them to test this idea, as well as others that students have come up with. Then ask students to record their findings on the worksheet

5.      Class chart: Make a class chart to describe what happened as a group.

6.      Storage: Students should keep their materials in the storage bags for use in the next lesson.

7.      Outcomes

• Student discover how rollers can reduce friction and allow an object to move down a ramp.