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Conservative and Non-Conservative Forces

Idea: It is not always true that the work done by an external force is stored as some form of potential energy. This is only true if the force is conservative:
Wc = Fcext(xB - xA) = PEA - PEB.      (5)
Definition: The work a conservative force does on an object in moving it from A to B is path independent - it depends only on the end points of the motion. Examples: the force of gravity and the spring force are conservative forces. For a non-conservative (or dissipative) force, the work done in going from A to B depends on the path taken. Examples: friction and air resistance.