SECTION 1 (PART 2): Types of Friction

WARM-UP: You push a skateboard on a flat surface.

According to Newton’s 1st Law of Motion what should happen?

Does this happen?

Why?

LEARNING GOALS Describe the four different types

of friction. Observe the effects of air

resistance on falling objects.

FRICTION Friction: a force that opposes

motion between two surfaces that are touching each other.

Why does this happen?

FRICTION Microwelds form when

microscopic dips and bumps that occur on a surface, no matter how smooth it may seem, come into contact with another surface.

FRICTION The greater the force pushing the two surfaces

together, the stronger the microwelds will be, which causes greater friction. For an object to move, the force must be strong enough to overcome the microwelds.

TYPES OF FRICTION

There are 4 main types of friction: Static Sliding Rolling Fluid

STATIC FRICTION Occurs between two

surfaces that are touching, but not moving past each other.

The object will not move.

SLIDING FRICTION Force that opposes

the motion of two surfaces sliding past each other.

ROLLING FRICTION Friction between the rolling

object and the surface it rolls on

FLUID FRICTION Occurs when a solid object is in

contact with a fluid (a gas or liquid) and a force is applied to either the object or to the fluid

Friction

COEFFICIENT OF FRICTION Number which represents the

friction between two surfaces

Ranges from 0 -1

COEFFICIENT OF FRICTION The higher the

coefficient, the greater the friction between the two surfaces

SOLVING FOR THE COEFFICIENT OF FRICTION

f = coefficient of friction (no units)

Fdrag = the force it takes to drag

the object in its normal direction of

travel

Fgravity = the weight of the same

object in the same units as the

drag force

f =Fgravit

y

Fdra

g

EXAMPLE A book has a weight of 5 N. It takes 3 N

of force to drag the book across the surface of a sidewalk. What is the coefficient of friction?