friction and inclined planes
DESCRIPTION
Friction and Inclined Planes. Friction. Friction – force that opposes motion Caused by microscopic irregularities of a surface The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it. . Friction. Friction. - PowerPoint PPT PresentationTRANSCRIPT
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Friction and Inclined Planes
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Friction – force that opposes motion Caused by microscopic irregularities of a surface
The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it.
Friction
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Friction
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Depends on the normal force and the type of
surfaceFf=mFN
Ff – force of friction (N) FN – normal force m – coefficient of friction (1 or less)
Friction
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Ratio of the frictional force to the normal
force
m
The coefficient of friction is a unitless constant that is specific to the material type and usually less than one
Coefficient of Friction
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Three types of friction1. Static – object at rest2. Kinetic – object in motion3. Rolling- object on
wheels
Types of Friction
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Friction depends only on
1) the nature of the two surfaces in contact 2) the normal force
It does not depend on the surface area.
Friction
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If the coefficient of kinetic friction between a 35-kg crate
and the floor is 0.30, what horizontal force is required to move the crate to the right at a constant speed across the floor?
If the object is on a level surface, then the normal force = weight force. If the object is moving at constant speed, then frictional force = only force. Ff = mFN FN = mg Ff = (0.30)(35)(9.8) FN= (35) (9.8) Ff = 102.9 N
Friction and Newton’s First Law
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Suppose the same 35 kg crate was not moving
at constant speed but accelerating at 0.70 m/s2. Calculate the applied force.
For horizontal forces with friction: Fapp= Fnet + Ff
Fapp = ma + mFN
Fapp = ma + mmg Fapp= (35) (0.70) + (0.3)(35)(9.8) Fapp= 24.5 + 102.9 = 127.4 N
Friction and Newton’s Second Law