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.
Mechanical energy. Work is done upon an object whenever a force acts upon it to cause it to be displaced. Work is a force acting upon an object to cause a displacement. In all instances in which work is done, there is an object which supplies the force in order to do the work.