SECTION 1 (PART 2):
Types of Friction
WARM-UP:
 You push a skateboard on a flat surface.
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According to Newton’s 1 Law of Motion what
should happen?
 Does this happen?
 Why?
LEARNING GOALS
 Describe the four different types of
friction.
 Observe the effects of air resistance on
falling objects.
FRICTION
 Friction: a force that opposes motion
between two surfaces that are touching each
other.
 Why does this happen?
FRICTION
 Microwelds form when
microscopic dips and bumps
that occur on a surface, no
matter how smooth it may
seem, come into contact
with another surface.
FRICTION
 The greater the force pushing the two surfaces together, the
stronger the microwelds will be, which causes greater friction. For
an object to move, the force must be strong enough to overcome
the microwelds.
TYPES OF FRICTION
 There are 4 main types of friction:
 Static
 Sliding
 Rolling
 Fluid
STATIC FRICTION
 Occurs between two
surfaces that are
touching, but not moving
past each other.
 The object will not move.
SLIDING FRICTION
 Force that opposes the
motion of two surfaces
sliding past each other.
ROLLING FRICTION
 Friction between the rolling object and
the surface it rolls on
FLUID FRICTION
 Occurs when a solid object is in contact with
a fluid (a gas or liquid) and a force is applied
to either the object or to the fluid
Friction
COEFFICIENT OF FRICTION
 Number which represents the friction
between two surfaces
 Ranges from 0 -1
COEFFICIENT OF FRICTION
 The higher the
coefficient, the
greater the
friction between
the two surfaces
SOLVING FOR THE
COEFFICIENT OF FRICTION
f=
Fdrag
Fgravity
f = coefficient of friction (no units)
Fdrag = the force it takes to drag the object
in its normal direction of travel
Fgravity = the weight of the same object in
the same units as the drag force
EXAMPLE
 A book has a weight of 5 N. It takes 3 N of force
to drag the book across the surface of a sidewalk.
What is the coefficient of friction?