C H A P T E R

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C H A P T E R   4Forces and Newton's Laws of
Motion
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4.9 Static and Kinetic Frictional Forces
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4.9 Static and Kinetic Frictional Forces
There are situations where friction helps us and
at other times it is a hindrance.
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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
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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.
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Microscopic view of Frictional Forces
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Frictional force VERSUS Applied force
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Frictional force VERSUS Applied force
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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
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Kinetic Frictional Force
The magnitude fk of the kinetic frictional force
is given by,
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Coefficients of Friction
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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?
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4.10 The Tension Force
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Free-body Diagram
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Object on an Inclined Plane
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Object on an Inclined Plane
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Problem-73
A cable is lifting a construction worker and a
crate, as the drawing shows. The weights of the
worker and crate are 965 and 1510 N,
respectively. The acceleration of the cable is
0.620 m/s2, upward. What is the tension in the
cable (a) below the worker and (b) above the
worker?
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Free-Body Diagram