Chapter 5 Section 3

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 together2. The roughness of the surfaces that are touching

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)

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

Types of Friction1. Kinetic Friction: friction between moving

surfaces2. Static Friction: a force is applied, but the

amount of friction balances it out…so the object doesn’t move.

Friction: Harmful and Helpful Helpful:

1. Tires/pavement: allows a car to move2. Brakes/wheels: stops the car3. Feet/floor: allows you to wall

Harmful:1. Causes holes in socks and in knees of jeans2. Wind and water erodes topsoil3. Friction between engine parts will cause

overheating

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