friction and inclined planes

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Friction and Inclined Planes

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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 Presentation

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Page 1: Friction and Inclined Planes

Friction and Inclined Planes

Page 2: 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

Page 3: Friction and Inclined Planes

Friction

Page 4: Friction and Inclined Planes

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

Page 5: Friction and Inclined Planes

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

Page 6: Friction and Inclined Planes

Three types of friction1. Static – object at rest2. Kinetic – object in motion3. Rolling- object on

wheels

Types of Friction

Page 7: Friction and Inclined Planes

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

Page 8: Friction and Inclined Planes

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

Page 9: Friction and Inclined Planes

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