1. Chapter 5-2 The Foundations of Physical Science
FORCES
Chapter 5-2
The Foundations of Physical Science

2. FRICTION Friction is a force that resists motion
Friction is found EVERYWHERE in our world
Examples: You feel friction when you swim, ride in a car, walk, and even when you sit in a chair
Friction can act when an object is moving or when it is at rest

3. Causes of Friction Two surfaces are involved
Friction depends on both of the surfaces that are in contact
Think of a hockey puck on ice or sandpaper --- there is a difference
Water and other liquid, such as oil, can greatly reduce friction between surfaces

4. Direction of the Friction Force
Friction is a force- like all forces-- it is measured in newtons
Friction resists motion
STATIC FRICTION- the friction force that resists the motion between two surfaces that are not moving

5. Identifying friction forces
SLIDING FRICTION- the friction force that resists the motion of an object moving across a surface
Example: pushing a box across the floor

6. Static Friction and Sliding Friction
How do the two compare?
It is harder to get something moving than it is to keep it moving
Static friction is almost always greater than sliding friction at slow speeds

7. Reducing the Force of Friction
Unless a force is constantly applied, friction will slow all motion to a stop eventually
It is impossible to completely eliminate friction

8. Friction can be useful!!! Brakes They are on bikes, motorcycles, cars
Cleated shoes
Shoes are designed to increase friction between your foot and ground

10. FRICTION AND ENERGY
Earlier we learned that energy moves through the action of forces
Energy changes into different forms
Friction changes energy of motion into heat energy
You feel the EFFECT of friction changing energy of motion into heat