1. Friction
What factors determine the strength of the friction force between two surfaces?

2. Key Terms Friction Static friction Sliding friction Rolling friction
Fluid friction

3. What is Friction?
The force that 2 surfaces exert on each other when they rub against each other.

4. What are the Causes of Friction?
The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved.
Smooth surfaces have less friction; bumpy surfaces have more
Friction acts in a direction opposite to the direction of the object’s motion

5. What is Static Friction?
Friction that acts on objects that are not moving
Because of static friction, you must use more force to start the motion of stationary objects
Once you start an object moving there is no longer static friction

6. What is Sliding Friction
Occurs when 2 solid surfaces slide over each other
Examples: spreading sand on icy path
Ballet dancers applying resin to ballet slippers so they don’t slip
Bicycle brakes
Skinning your knee

7. What is Rolling Friction
Occurs when an object rolls across a surface
Easier to overcome than sliding friction for similar materials
Ball bearings are in moving objects such as skates, skateboards, and bicycles
Ball bearings reduce friction by rolling between moving parts

8. What is Fluid Friction Occurs when solid objects move through a fluid
Easier to overcome than sliding friction
Reason why moving parts are often bathed in oil or other lubricants
Fluid friction occurs between a bicyclist and the air. Bicyclists often wear streamlined helmets and clothes