Friction

Chapter 5 Section 3

Objectives:

Explain why friction occurs

List the 2 types of friction, and give examples of each type

Explain how friction can be both harmful and helpful

FYI: Sports & Friction

Runners want friction! (shoes)

Surfers wax their board to decrease friction

Downhill skiers wax their skis to decrease friction

Friction:

A force that opposes motion between 2 surfaces that are

in contact

Can cause a moving object to slow down or stop

The Source of Friction

Surfaces of objects are rough (even when they appear

smooth)

Contact causes friction

The amount of friction depends on many factors:

The force pushing

The surfaces together

The roughness of the surfaces

The Effect of Force on Friction:

The amount of friction depends on the force pushing the

surfaces together

Objects that weigh less, exert less downward force

Changing how much of the surfaces come in contact does

not change the amount of friction

The Effect of Rougher Surfaces on

Friction:

Rough surfaces: more hills & valleys, greater friction

Ball rolling down a rough surface vs. hockey puck on a

smooth surface

Types of Friction:

Kinetic Friction:

Friction between moving surfaces

Sliding, rolling

Ex: brakes on a bicycle, pencil on paper, in-line skates

Static Friction:

“Not moving”

Force is applied to an object but does not cause it to move

Friction: Harmful & Helpful

Erosion

Holes in your socks

Heat up moving parts

Brakes on a car

Pencil & paper to make a mark…

Some Ways to Reduce Friction:

Lubricants – reduce friction

Motor oil

Wax

Grease

Gas (air) on an air hockey table

Smooth the surfaces – reduce friction

Sandpaper

Some Ways to Increase Friction:

Make surfaces rougher – increase friction

Sand or salt scattered on icy roads

Textured gloves for baseball or football players

Increase the force pushing the surfaces together

Applying more force when sanding a rough piece of wood

Quick Quiz:

Which of the following would NOT help you move a

heavy object across a concrete floor?

Water, ball bearings, oil, liquid, soap, steel rods, foam rubber

Name 3 common items you might use to increase

friction.