Work and EnergyWork and Energy

Conservation of EnergyConservation of Energy

Conserved QuantitiesConserved Quantities

Conserved – remains constantConserved – remains constant

– May change formMay change form

Mass and energy are both conservedMass and energy are both conserved

Conserved QuantitiesConserved Quantities

Mechanical EnergyMechanical EnergyMechanical energy – the sum of kinetic Mechanical energy – the sum of kinetic energy and all forms of potential energyenergy and all forms of potential energy– Typically involves things we can seeTypically involves things we can see

Not atomic or chemical energiesNot atomic or chemical energies

Mechanical energy = kinetic energy + sum Mechanical energy = kinetic energy + sum of all potential energiesof all potential energiesME=KE+ME=KE+ΣΣPEPENon-mechanical energy – energy that is Non-mechanical energy – energy that is not mechanical, such as nuclear, chemical, not mechanical, such as nuclear, chemical, internal, and electricalinternal, and electrical

Mechanical EnergyMechanical Energy

Mechanical EnergyMechanical Energy

Conservation of mechanical energy – Conservation of mechanical energy – in the absence of friction, the total in the absence of friction, the total amount of mechanical energy in a amount of mechanical energy in a system is conservedsystem is conserved

Initial mechanical energy = final Initial mechanical energy = final mechanical energymechanical energy

MEMEii=ME=MEff

Mechanical EnergyMechanical Energy

Mechanical EnergyMechanical Energy

Other than friction, mechanical Other than friction, mechanical energy is conserved in the presence energy is conserved in the presence of forces acting on an objectof forces acting on an object

Mechanical energy is conserved Mechanical energy is conserved when an object experiences variable when an object experiences variable accelerationacceleration

Friction and Mechanical EnergyFriction and Mechanical Energy

Mechanical energy is not conserved Mechanical energy is not conserved in the presence of frictionin the presence of friction– Total energy is still conservedTotal energy is still conserved

Total energy is always conserved in non-Total energy is always conserved in non-nuclear reactionsnuclear reactions

Friction converts mechanical energy Friction converts mechanical energy into non-mechanical energies such into non-mechanical energies such as sound and heatas sound and heat

Friction and Mechanical EnergyFriction and Mechanical Energy