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Friction and Inclined Planes

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.

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Friction and Inclined Planes

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  1. Friction and Inclined Planes

  2. 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.

  3. Friction

  4. Friction • Depends on the normal force and the type of surface Ff=mFN • Ff– force of friction (N) • FN – normal force • m – coefficient of friction (1 or less)

  5. Coefficient of 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

  6. Types of Friction • Three types of friction • Static – object at rest • Kinetic – object in motion • Rolling- object on wheels

  7. 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.

  8. Friction and Newton’s First Law • 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 = mFNFN= mg • Ff = (0.30)(35)(9.8) FN= (35) (9.8) • Ff = 102.9 N

  9. Friction and Newton’s Second 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

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