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.
Forces change motion. A force is a push or a pull. Forces give energy to objects to cause them to start moving, stop moving, change direction, or change the shape of objects. Forces are required to accelerate an object. Types of Forces: 1) Contact Force is when one object pushes or pulls an object by touching it. 2) Gravity is the force of attraction between two masses. 3) Friction is the force that resists motion between two surfaces in contact with each other.