© Left: Jon Ovington, Creative Commons Attribution-ShareAlike 2.0 Generic License. Right: Benjamin Crowell, lightandmatter.com, Creative Commons Attribution-ShareAlike 3.0 License.
The picture on the right represents a conservative force (gravity) in action. The picture on the left shows the effect of a non-conservative force (friction). For macroscopic forces, the action of conservative forces are easily reversible—one can carry the inner tube back up the hill—while that of non-conservative forces is not—the heat energy emitted by the tire cannot be put back into the kinetic energy of the car. (Unit: 2)