Friction

Friction: a force that opposes motion between two surfaces that are in contact.

Friction can cause a moving object to slow down and eventually stop.

StaticFriction

When a force is applied to an object but does not cause the object to move.

Static means “not moving”

Contrasting examples…walking on asphalt and walking on ice

Kinetic Friction

The friction between 2 moving surfaces

There are 2 main types:◦Sliding friction◦Rolling friction

SlidingFriction(kinetic friction)

Force of sliding friction is usually greater than the force of rolling friction.

Example…ever tried to slide really large and heavy objects?

Rolling (Kinetic Friction)

The force of rolling friction is smaller than sliding friction.

If you put that large heavy object on wheels it be much easier to move!

FluidFriction

This includes air resistance as well as resistance in a liquid

Example…sky diving and swimming in a pool

FrictionReview

Brakes in cars work by pressing pads together within the car’s wheel assembly. This resistance to the motion off the car results from which of the types of friction?

Sliding friction

The force of friction between a rock and the ground just before the rock starts to slide down a mountain slide.

Static friction, sliding friction, rolling friction or air resistance

The force of friction between a bike tire and the road as a cyclist skids to a stop

Static friction, sliding friction, rolling friction or air resistance

The force of friction that slows down a skier if she doesn’t wax the bottom of her skis.

Static friction, sliding friction, rolling friction or air resistance

The type of friction that you would want to increase if you were trying to walk across a large sheet of slick ice.

Static friction, sliding friction, rolling friction or air resistance

Friction Review

Put the different types of friction in order of strongest force to weakest force.

Static friction is strongest, followed by sliding friction, and then rolling friction, which is weakest.

The type of friction that athletes often try to reduce by wearing tight fitting outfits during races.

Static friction, sliding friction, rolling friction or air resistance

What is the force of friction between a rock and the ground just before the rock starts to slide down a mountain slide?

What is the force of friction between a bike tire and the road as a cyclist skids to a stop?

What is the force of friction that slows down a skier if she doesn’t wax the bottom of her skies?

What is the type of friction that you would want to increase if you were trying to walk across a large sheet of slick ice?

What is the type of friction that athletes often try to reduce by wearing tight fitting outfits during races?