Download Ch4 friction

4.9 Static and Kinetic Frictional Forces
There are situations where friction helps us and at other times it
is a hindrance.
Advantages of friction:
Disadvantages of friction: wear and tear & energy loss.
Microscopic view of
Frictional Forces
Frictional force VERSUS
Applied force
Frictional force VERSUS
Applied force
Static Frictional Force
The magnitude fs of the static frictional force can have any
value from zero up to a maximum value of fsMAX, depending
on the applied force.
fs ≤ fsMAX
fsMAX = m sFN
Kinetic Frictional Force
The magnitude fk of the kinetic frictional force is given by,
f k  m k FN
Coefficients of Friction
EXAMPLE 10 Sled Riding
A sled is traveling at 4.00 m/s along a horizontal stretch of
snow, as Figure 4.23a illustrates. The coefficient of kinetic
friction is mk = 0.0500. How far does the sled go before
stopping?
4.10 The Tension Force
56. Part a of the drawing shows a
bucket of water suspended from the
pulley of a well; the tension in the
rope is 92.0 N. Part b shows the
same bucket of water being pulled
up from the well at a constant
velocity. What is the tension in the
rope in part b?
Object on an Inclined Plane
43.
A Mercedes-Benz 300SL is parked on a road that
rises above the horizontal. What are the
magnitudes of (a) the normal force and (b) the
static frictional force that the ground exerts on the
tires?
57.
A worker stands still on a roof sloped at an angle
of above the horizontal. He is prevented from
slipping by a static frictional force of 390 N. Find
the mass of the worker.