A force is said to be conservative if the work done by or against it in moving an object is independent of the object's path. The work done by a conservative force depends only on the initial and final positions. Gravity is one example, the spring force another.
The work done by a nonconservative force depends on the path through which the force acts. The most common example is this kind of force is friction. You can study the action of a conservative force, gravity, and a non-conservative force, friction, in the work applet in this chapter. As long as you lift the box in this applet off the ground, you can make it take any path, and when you return the box to its initial position, the total work done will be 0. But if you slide it back and forth along the ground, the work will always increase.
Question:
Why is this distinction important?
Answer:
As we will see next, only conservative forces conserve the total mechanical energy of a system.
Question:
Do non-conservative forces therefore violate the law of total energy conservation?
Answer:
No, the law of total energy conservation is always valid. But non-conservative forces convert some of the mechanical energy into other energy forms, such as heat.
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