1. FRICTION

2. The force that slows the ball to a stop is FRICTION.
What will happen when the ball is released?
When the ball reaches the bottom of the slope, will it keep moving forever?
The force that slows the ball to a stop is FRICTION.
Since the ball stops, there must be a force acting to slow the ball down.

3. 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.
Direction of Motion
Friction Force

4. Direction of Intended Movement
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

5. Sliding 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

6. 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.
Direction of Motion
Friction Force

7. Types of Friction
Fluid friction occurs when a solid object moves through a liquid or gas.
Air resistance is a type of fluid friction.
Direction of Motion
Friction Force

8. 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.
FLUID FRICTION
SLIDING FRICTION
ROLLING FRICTION
STATIC FRICTION
Friction Force

9. 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?

10. Review of Friction Forces

11. 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!
Direction of Motion
Friction Force

12. 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

13. 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

14. Conclusions Questions
Which surface material created the MOST frictional force?
Which surface material created the LEAST frictional force?
Give an example of a situation where we use a certain surface material to:
a) REDUCE friction
b) INCREASE friction