What Do We Mean When We Speak About Surfaces in Contact? 1 © 2009 McREL Physical Science Lesson 2 What Do We Mean When We Speak About Surfaces in Contact? What factors can INCREASE contact area? Investigating Static Forces in Nature: The Mystery of the Gecko

What Do We Mean When We Speak About Surfaces in Contact? 2 © 2009 McREL Contact Between Shoe and Floor Identify the amount of contact between each of these shoes and the surface. Image 2.1

What Do We Mean When We Speak About Surfaces in Contact? 3 © 2009 McREL Contact Between Shoe and Floor Now closer up, did your answer change? Why or why not? Label the contact points on the image in your journal. Image 2.2 Image 2.3 Image 2.4

What Do We Mean When We Speak About Surfaces in Contact? 4 © 2009 McREL Comparing Surfaces Compare the amount of surface contact possible with each shoe. Label the contact points on the image in your journal. Image 2.5 Image 2.6 Image 2.7

What Do We Mean When We Speak About Surfaces in Contact? 5 © 2009 McREL Determining Contact to Total Surface Ratio Determine the ratio of contact area to total area of your shoe. Sole of shoeContainer of ground chalk Coating the sole of the shoe with chalk Image 2.8Image 2.9Image 2.10

What Do We Mean When We Speak About Surfaces in Contact? 6 © 2009 McREL Determining Contact to Total Surface Ratio Determine the ratio of contact area to total area of your shoe. Image 2.11Image 2.12

What Do We Mean When We Speak About Surfaces in Contact? 7 © 2009 McREL Apparent vs. Real Contact Area apparent contact area real contact area hard If both surfaces are hard: only a small percentage of the apparent contact area is in real contact. Image 2.13 Image 2.14

What Do We Mean When We Speak About Surfaces in Contact? 8 © 2009 McREL Making Connections 1.Describe one or two ideas that you learned during this lesson. 2. What factors affect the amount of contact area between two surfaces? 3.What new ideas do you have about how the gecko sticks to the ceiling? 4.What should we explore next?

What Do We Mean When We Speak About Surfaces in Contact? 9 © 2009 McREL Flow Chart 2. What Do We Mean When We Speak About Surfaces in Contact? Scale: Visible Force: Gravity Tools: Eyes 3. What Are Your Ideas of Small Sizes? 7. How Do We Measure Forces at the Nano Level? 1. How Can a Gecko Walk on a Ceiling? Scale: Visible Dominant Force: Gravity Tools: Eye 5. What Types of Forces Can Hold Objects Together? 8. How Can a Gecko Walk on a Ceiling? 4.What Do We Learn When We Look More Closely? 6. How MUCH Force Is Needed to Make an Object Stick? What Factors Affect the STRENGTH of Force Acting?