# 4. Surfaces and Friction

## Overview

Students begin with ramps that are at the height that would make the sled move in Lesson 3. They vary the surface of the slide. What effects do these different surfaces have?

## Materials

• Ramps, ramp stands and sleds from Lesson 3 (six per group)
• Materials for making new surfaces: approximately 8″ x 10″ sheets of aluminum foil, wax paper, sand paper, cardstock and felt (one sheet per group)
• Bull dog clips or Paper clips for attaching materials to ramps
• Scissors for cutting out samples of surfaces, and glue for attaching these to worksheet (as alternative to writing their names)

## Procedure

1. Setting up six surfaces:
Set up or help students set up six ramps per group, adjusted to the minimum height to make the sled go down (discovered in Lesson 3.) Attach a different surface to each ramp, except one, which should be left bare. The six ramps should have the following surfaces: aluminum foil, felt, sand paper, wax paper (crumpled), card stock, and plain cardboard

• Review the names of these materials and make a large chart showing a sample of each one and its name.
• Conduct a discussion about how they are different. How does each surface feel when you touch it? Help students develop their words for describing the various textures, such as “hard,” “soft,” “rough,” “smooth,” “crinkly,” “scratchy,” etc.

2. Predicting what each surface will do:

• Will the sled be able to go down each one?
• On which ones will it get stuck?
• Conduct a class discussion about what will happen when they let the sleds go.
• Why does the sled get stuck?
• Which of the surfaces will act like the heavy coat or blanket?
• Which one is most like a bare slide? Introduce the word friction as a word scientists use to describe how things that want to move might get slowed down or stuck, and kept from moving.

3. Doing the experiment and recording data:
Ask students to test each ramp, and record the results on the worksheet. Students can identify each surface by writing its name, or by gluing a small sample of each one onto the worksheet.

4. Class chart:
Create a chart with the class that lists all the surfaces the students tried. Beside each surface record the lowest height that the slider was able to slide on.

5. Outcomes:

• Students explore surface and textures and develop vocabulary for describing each one.
• Students investigate how different kinds of surfaces make it easier or harder for something to slide down, relating this to their own experiences on playground slides.
• Students classify surfaces according to their types, and record what the sled did on each surface.