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
Friction and Inclined Planes
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
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
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
Three types of friction1. Static – object at rest2. Kinetic – object in motion3. Rolling- object on
wheels
Types of Friction
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
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
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