My lecturer defined that tension can be both conservative and non conservative. I'm not sure exactly when the non-conservative part comes in. Hope somebody can help. From my understanding: Conservative forces do not alter the Mechanical energy of the system Work done around a closed loop by a conservative force is zero Work done by a conservative force is independent of path taken (i.e. only the final and initial coordinates of the displacement are needed) So, I can define tension as being conservative in the example of a hockey puck swinging in a constant velocity in a circular loop, tied to the centre by a string. There is a tension force acting at all times that is effectively the radial force, but the hockey puck's KE does not change, hence its EMech does not change. (I zeroed PE). But when is a tension force non-conservative? I.E it fails to satisfy any of the listed conditions above.