What causes a force field to be "non-conservative?"?

Question

A [conservative force](http://en.wikipedia.org/wiki/Conservative_force) field is one in which all that matters is that a particle goes from point A to point B. The time (or otherwise) path involved makes no difference. Most force fields in physics are [conservative](http://en.wikipedia.org/wiki/Conservative_vector_field) (conservation laws of mass, energy, etc.). But in many other applications, the time paths DO matter, meaning that the force field is not "conservative." What causes a force field to be "non-conservative?" Could you give some examples (probably outside of physics)?

Answer 1

Well, the "poster child" (meaning best-known example) of a non-conservative force would be friction, as well as similar, friction-like forces such as air resistance. The work done by these forces depends on the specific path taken, and is not reversible by moving in the opposite direction. There is no useful potential energy storage due to these forces, though you could start a fire by friction.