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.
The total mechanical energy of an object is the sum of its kinetic energy and potential energy. If the object is moving the kinetic energy equals one half times the mass (m) of the object times (t) the square of the speed (v) of the object: E=1/2*m*v2.