1. Chapter 5 Section 3

2. The Source of Friction  The surface of ANY object is rough. Even smooth surfaces have tiny hills and valleys  When two objects touch, the hills and valleys get stuck to each other.  The amount of friction is determined by: 1. The force pushing the surfaces together 2. The roughness of the surfaces that are touching

3. The Effect of Force on Friction  If the force increases, the amount of friction increases (the hills and valleys “catch” harder)  If the force decreases, the amount of friction decreases (they won’t “catch” as much)

4. The Effect of Surfaces on Friction  The rougher the surface, the more friction it will have  The smoother the surface, the less friction it will have

5. Types of Friction 1. Kinetic Friction: friction between moving surfaces 2. Static Friction: a force is applied, but the amount of friction balances it out…so the object doesn’t move.

6. Friction: Harmful and Helpful  Helpful: 1. Tires/pavement: allows a car to move 2. Brakes/wheels: stops the car 3. Feet/floor: allows you to wall  Harmful: 1. Causes holes in socks and in knees of jeans 2. Wind and water erodes topsoil 3. Friction between engine parts will cause overheating

7. How to Increase and Decrease Friction  Decrease  Use lubricants (motor oil, wax, grease)  Ball bearings on wheels makes them easier to roll  Make the surfaces smoother  Increase  Make surfaces rougher  Increase the force pushing the surfaces together