Understanding Friction Force Direction & Identification of Relative Motion

AI Thread Summary
The direction of friction force always opposes the relative motion between surfaces. Relative motion refers to the movement of one surface in relation to another. To identify the direction of friction, observe the movement from the reference frame of the surface exerting the friction. For instance, if surface A moves left relative to surface B, the friction force on A acts to the right. Understanding these principles is crucial for accurately determining friction forces in various scenarios.
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Direction of friction force is oppose relative motion of the surface .
What is relative motion of the surface mean and how to identify the direction of the relative motion of the surface .
 
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Friction forces always oppose slipping of the surfaces. When sliding does occur, it's easy to find the direction of the friction. If surface B exerts friction on surface A, then you can find the direction of the friction force on A by viewing things from the reference frame of B. If A moves to the left with respect to B, then the friction force on A acts to the right. (Of course, the friction force that A exerts on B is equal and opposite to the friction force that B exerts on A.)
 

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