Linear Motion Kinematics Circular Kinematics Forces & Linear Motion Friction Forces Work & Energy
Friction Forces
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Friction
Forces
When two surfaces are in contact, there is a force between them, the friction
force, which is parallel to the surface and tends to oppose the
sliding motion of the surfaces.
When the sufaces are sliding, the friction force (which opposes the
external forces which produce the motion) is given by Ff
= µkN,
where N
is the normal
or perpendicular force pushing the surfaces together, and µk
is the coefficient
of kinetic friction, a quantity which depends on the nature of the two
surfaces.
When the surfaces are not sliding, but there are external forces
attempting to produce sliding, the maximum friction force is given by Fs
= µsN,
where µs
is the coefficient
of static friction. When the external forces exceed the maximum
friction force, sliding begins.