Friction is the main nonconservative force we will encounter. To the extent that friction is present, energy will not be conserved. Well, that means "large scale, mechanical energy" will not be conserved. Friction produces heat and heat involves the microscopic motion of molecules. Energy is always conserved when thermal energy or heat is included. Usually, however, when we talk about Energy Conservation we mean
PEi + KE i = PEf + KE f
without including heat or thermal energy.
Energy Conservation More Examples Return to ToC, Potential Energy (c) 2005, Doug Davis; all rights reserved