FRICTION
What factors determine the
strength of the friction force
between two surfaces?
Key Terms





Friction
Static friction
Sliding friction
Rolling friction
Fluid friction
What is Friction?

The force that 2 surfaces exert on each other when
they rub against each other.
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
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
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
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
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