Elementary Classical Physics I Chapter 7: Conservation of Energy Conservation of Energy­ Energy cannot be created nor destroyed; however is can be transformed from one form to another 7.1 Conservative Forces and Nonconservative Forces Conservative Forces­ stores energy into a system, later given back in the form of work or kinetic energy Examples: 1) Spring Restoring Force 2) Gravitational Force 3) Static Electric Force Properties of Conservative Forces: 1) The work done by a conservative force by moving an object between 2 points is independent of the path taken 2) Work done ❑n a circular loop of a conservative force is zero a) ∮ Fdr=0 ❑ Nonconservative Forces­ forces that give energy to a system, the the system cannot give it back in the form of work. Converts into Microscopic Energy (Heat, Sound, etc) Example: Kinetic Friction Force 7.2 Potential Energy Potential Energy­ energy acquired by an object’s position ­ Energy stored (work/energy) associated with a conservative force 7.3 Conservation of Mechanical Energy 4 equations Wnet=ΔKE=­ΔU Kinetic energy change equals negative potential energy change 1) ΔKE=­ΔU Object Falling from Point A to Point B b Wnet= ∫gdr a b ¿mg dr ∫a ¿|mg|hAcos(0) POSITIVE WORK ¿|mg|hA 2) ΔKE+ΔU=0 ❑ ❑ ❑ ∫ ΔKE+ Δ∫= 0 ∫ ❑ ❑ ❑ 3) K+U=Constant (U+K)A+(U+KB =Constant Mechanical Energy of an object at any moment in time is constant 4) mechConstant