Energy & Work • Closely related • Energy: ability to do work • Work: transfer of energy • Both measured in Joules
Energy Types • Kinetic Energy: Energy in motion • Potential Energy:Stored energy (not moving) • depends on position or condition of object
Calculating KE KE = ½ mv2 m = mass v = velocity Which increases kinetic energy more: doubling the mass or doubling the velocity?
Examples of PE Boulder on top of cliff Firecracker battery
Elastic Energy(type of potential energy) • Energy stored in a compressed material • Example: rubber band, spring
Gravitational PE • PE that depends on object’s height, and weight G.P.E. = mgh m = mass g = 9.8 m/s2 h= height. Which will have greater GPE: a rock on a 3 story ledge or a rock on a 20 story ledge?
Forms of Energy • Mechanical Energy:Related to motion of objects • Ex : moving machine parts Windmill Engine piston
Mechanical Energy • PE Converts to KE and vice versa • Mechanical Energy = KE + PE • Total energy • Skier • Roller Coaster • Dart
Thermal Energy • Related to heat • Thermal Energy = total KE and PE of all particles in an object • Particles in matter are constantly moving
Chemical Energy(type of potential energy) • Energy stored in chemical bonds within a substance Ex: Gas, food, human body, battery
Electrical Energy • Energy of Electric Charges
Electromagnetic Energy • Energy traveling in the form of waves • X-rays Visible light
Nuclear Energy • Energy stored in nucleus of an atom • Nuclear Power plants convert nuclear energy to electricity
Energy conversions • Law of conservation of energy: • Energy cannot be created or destroyed, only converted from one form to another
Impact crater in Arizona formed within past 20 yrs Large KE of meteor converted to large amount of thermal energy vaporizing everything in Close proximity
Energy conversions • Light bulb : converts electrical into thermal and electromagnetic energy • Compressed Spring: converts potential to kinetic • Burning wood: stored chemical energy converted to thermal and electromagnetic
Energy Conversion in a Pendulum If friction is ignored total mechanical energy will remain constant (KE + PE) start = (KE + PE)end Pendulum would swing forever!!!
Viewing a Pendulum • Pendulum Energy Conversion