2.4 Friction

Part of Force and Translational Dynamics in AP® Physics 1: Algebra-Based. Read the opening section, then create a free account for the full interactive lesson, practice, and progress tracking.

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Kinetic Friction

In real life, friction is something you experience as the roughness of a surface. It makes 2 surfaces harder to slide past one another. Kinetic friction occurs when objects are sliding past one another and they are in contact. Kinetic friction acts to oppose the motion of the object sliding across a surface. Kinetic friction does not depend on the size of the contact. Kinetic Friction is represented with either the variable

{F_{f,k}}

or the variable

{f_k}

. The coefficient of kinetic friction is a value that shows how “rough” a surface is, and is proportional to the frictional force.

|F_{f,k}|=|\mu _kF_N|

${F_{f,k}}$ represents the frictional force
${\mu _k}$ represents the coefficient of kinetic friction
${F_N}$ represents the normal force that the object exerts on the surface

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