2. Conservative and Non-Conservative Forces The work to lift an object and to carry it up an incline plane are the same…simple machines save us force not work. Forces like lifting against gravity where the only thing that matters is the final and beginning points are called conservative forces. Forces like friction, where the path matters for the final amount of work are called non- conservative forces.

3. The Work Energy Principle With Potential Energy W nc =  KE +  PE

4. Mechanical Energy and Its Conservation E 2 + E 1 = Constant  KE +  PE =  KE 2 +  PE 2 Total mechanical energy is conserved… The principle of conservation of mechanical energy….if only conservative forces are acting, the total mechanical energy is conserved.

5. Problems Using Conservation of Mechanical Energy  KE +  PE g +  PE e =  KE 2 +  PEg 2 +  PEe 2 See examples 6-8, 6-9,6-10,6-11, 6-14

6. Homework P176 35-39 and 44