Public School, Deer Creek Minnesota, 1918 LakesnWoods.com Postcard and Postcard Image Collection - click image to enlarge Aerial view, Deer Creek Minnesota, 1972
Whenever work is done upon an object by an external force, there will be a change in the total mechanical energy of the object. If only internal forces are doing work (no work done by external forces), there is no change in total mechanical energy; the total mechanical energy is said to be conserved.
when an object is moving; energy of motion possessed by moving objects (mechanical); moving object becomes capable of doing work; energy of motion; work done on an object is equal to the change in energy gain by the object. (EX: faster moving hammer has more of this when it hits a nail than a slower one)