Friction FRICTION What factors

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Friction FRICTION What factors Powered By Docstoc
					           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