FRICTIONPg 29 of ISN

I can describe what determines the amount of

friction between two objects.

FRICTION

• What will happen when the ball is released?

• When the ball reaches the bottom of the slope, will it keep moving forever?

Since the ball stops, there must be a force acting to slow the ball down.

The force that slows the ball to a stop is FRICTION.

What is Friction?

• Friction is a force that two surfaces exert on each other when they rub against each other.

• The direction of the friction force is always OPPOSITE to the direction of the motion.

Friction Force

Direction of Motion

Types of Friction

• Static Friction opposes the motion of an object that is at rest

• To make the object move, you have to exert a force larger than the force of static friction.

Direction of Intended

Movement

Static Friction Force

Types of Friction

• Sliding friction occurs when two solids slide over each other.

• Sliding friction makes car brakes work and stops athletes from slipping.

Direction of Slide Sliding Friction Force

Types of Friction

• Rolling friction occurs when an object rolls across a surface.

• Rolling friction is easier to overcome than sliding friction for the same materials.

Friction Force

Direction of Motion

Types of Friction

• Fluid friction occurs when a solid object moves through a liquid or gas.

• Air resistance is a type of fluid friction.

Friction Force

Direction of Motion

Which type of friction is slowing down the object in each

situation?• You are slipping down a waterslide at

Emerald Pointe.

• You use a lot of force to slide a desk across the floor.

• You’re riding a skateboard down the street and it slowly rolls to a stop.

• You try to push the couch, but can’t seem to move it. Friction Force

SLIDING FRICTION

ROLLING FRICTION

FLUID FRICTION

STATIC FRICTION

Friction Thought Questions• Why would you add oil to a rusty bike

chain? • Why would you add sand to an icy

driveway or road?• Why is it easier to move heavy furniture

using a handcart rather than pushing it?• Why would a shoe company be interested

in studying friction?• What would happen if we repeated the

tug-of-war and one team had only socks on?

Review of Friction Forces

Review - What is Friction?

• Friction is a force that two surfaces exert on each other when they rub against each other.

• The direction of the friction force is always OPPOSITE to the direction of the motion.

• It SLOWS down moving objects!

Friction Force

Direction of Motion

What factors affect Friction?• In your homework, you found out 2

factors affect friction:– Types of surfaces involved– How hard the surfaces push

together• Today, we’re going to investigate

DIFFERENT SURFACES to see which ones create the most friction.

CARPET SANDPAPER DESK

Conclusions Questions1. Which surface material created the

MOST frictional force?

2. Which surface material created the LEAST frictional force?

3. Give an example of a situation where we use a certain surface material to:

a) REDUCE friction b) INCREASE friction