PLEASE TAKE OUT
YOUR HOMEWORK
Friction - a force that opposes
motion, or “pushes back” when
two surfaces are touching.
It’s always around and
it affects everything.
WITHOUT FRICTION…
FRICTION- WORKS AGAINST YOU …..BUT IT
CAN BE HELPFUL!
WHEN DO I WANT…
A lot of friction?
 http://www.youtube.com/watch?v=yTKwS-J7qVE
A little bit of friction?

http://digg.com/video/the-science-of-figure-skating
 http://www.nbclearn.com/olympics
FRICTION TYPES AND PARTS…
There are three Basic Types of
Friction
Static
Kinetic
Fluid
TYPES OF FRICTION:
1) Static friction: Friction that resists
the initiation (start) of sliding motion
between two objects at rest.
Keeps things stopped
TYPES OF FRICTION:
2) Kinetic friction: The force that
opposes the movement of two surfaces
that are in contact and moving over
each other.
To make something move, you just overcome static friction by pulling
with a force larger than kinetic friction.
TWO TYPES OF KINETIC FRICTION:
a) Sliding – the objects are sliding
b) Rolling – the objects are rolling.
Rolling is usually less than sliding.
TYPES OF FRICTION:
3) Fluid friction: The friction between
layers of a fluid.
2 types- Liquid and Gas
Liquid- water, oil etc.
Gas - Air
TYPES OF FRICTION:
Described by viscosity.
Viscosity – the “thickness” of a fluid.
Low viscosity = “thin;”
High viscosity = “thick” or “viscous.”
The less viscous a fluid is, the easier it
moves.
Friction DOES depend upon:
1. surface area in contact
2. mass/gravity (weight) of object
3. coefficient of friction –
“mu”(the texture of the
surface)
FRICTION IS CUMULATIVE
Small amounts of friction in a
system add up to become a large
amount of friction.
TEXTBOOK FRICTION…CHALLENGE