Conservation of Energy Section 4.2 Pictures from phys/Class/energy/u5l1b.html

Changing Forms of Energy Many devices convert energy from one form to another Many devices convert energy from one form to another –Electrical to thermal –Mechanical to Electrical In Vehicles: In Vehicles: –Engine: Chemical Energy to Kinetic energy –Spark plug: Electrical Energy converts gasoline’s chemical energy to thermal energy –Thermal Energy causes gases to expand –Expanding is mechanical energy, which moves parts of the car = kinetic energy

Conversions Between Forms of Energy Plants: light into chemical Plants: light into chemical –Uses E from sunlight to make bonds Mechanical energy – total KE and PE in a system Mechanical energy – total KE and PE in a system –ME = KE + PE G + PE e Amount of ME is due to: Amount of ME is due to: –Position and Motion Can PE be converted into KE? Can PE be converted into KE?

Falling Skater When an object falls When an object falls –Before release: All E is PE –As it falls, PE is converted to KE –At the bottom of the fall, all is KE ME remains the same ME remains the same See pg 109 for baseball See pg 109 for baseball See next slide for swing See next slide for swing

Law of Conservation of Energy Energy cannot be created or destroyed. Energy cannot be created or destroyed. –E is constant in universe –Can only be transformed from one type to another Energy can be transformed into non-useful forms, like heat Energy can be transformed into non-useful forms, like heat “Disappearing energy” – doesn’t disappear “Disappearing energy” – doesn’t disappear –Is converted into thermal energy by friction

Energy Energy in sun- from transformation of mass into energy Energy in sun- from transformation of mass into energy –Fusion: 2 H nuclei  helium nucleus + neutron + energy Nuclear Power Plants- Energy from fission- break apart nuclei Nuclear Power Plants- Energy from fission- break apart nuclei –In fission and fusion, mass and energy TOGETHER are conserved –Fission: uranium + neutron  Xe + Sr + neutrons + energy

Energy in You Kinetic energy: Kinetic energy: Thermal energy: Thermal energy: Chemical energy: Chemical energy: Electrical energy: Electrical energy: