Kinetic and Potential EnergyWorkWorkWork W=FdWork W=FdWork W=FdWork W=FdWork W=FdWork W=FdPowerPower P = energy/timePower P = energy/timeWork vs. EnergyWork vs. EnergyWork vs. EnergyWork vs. EnergyPotential EnergyPotential EnergyGravitational potential energyGravitational potential energyGravitational potential energyGravitational potential energyGravitational potential energyGravitational potential energyGravitational potential energyWork, Power and EnergyWork, Power and EnergyWork, Power and EnergyWork, Power and EnergyKinetic Energy of MotionKinetic Energy of MotionKinetic Energy of MotionConservation of EnergyConservation of EnergyConservation of EnergyConservation of EnergyConservation of EnergyConservation of EnergyConservation of EnergyConservation of EnergyWork, Power and EnergyWork, Power and EnergyWork, Power and EnergyWork, Power and EnergyKinetic Energy of MotionKinetic and Potential EnergySupplemental Text MaterialPages 326-333WorkTransference of EnergyWork = Force x distanceW=FdWork• Lifting load against the force of the weight of the object• Twice the distance results in twice the work• Twice the weight is twice the workWork W=Fd• Twice the weight• Twice the distanceWork W=Fd• Weight lifter expends energy to keep the potential energy in the barbell• But he does no work on the barbell after it is liftedWork W=FdWork W=FdUnits of force = Newtons = Force x distance = Newton meters==Joules2smkg⋅222smkgmsmkg ⋅=⋅⋅• Units of work are Joules• Work is energyWork W=Fd• Nothing about time in definition• Slow or fast• Same force, same distance = same workWork W=FdPower•Work W=Fd• Power = work / time• Units Joules/secondssmkg÷⋅22=•⋅ssmkg 122=⋅ssmkg22/wattsmkg=⋅32Power P = energy/time• Half the time=Twice the power• Twice the time=Half the powerwattsmkg=⋅32• Fuel burn• Biodieselhttp://www.alternativefuels.com.au/Biodiesel/dragster.htmhttp://www.lilligren.com/Redneck/redneck_lawnmower.htmPower P = energy/time• Same units• Work occurs with transfer of energy• Work occurs when you store potential energyWork vs. Energy• Energy stored in bow• Work is done to create the potential energyWork vs. Energy• Lift heavy ram of pile driver• Work transfers energy to lift into potential gravitational energyWork vs. EnergyMechanical energyMoving things—has two forms1. Potential mechanical energyWaiting to work2. Kinetic mechanical energy Work being doneWork vs. EnergyPotential Energyhttp://www.howstuffworks.com/inside-clock.htm• http://www.himalayan.pdx.edu/virtualjourney/slideshow/se_photos_web/pages/Boy%20with%20Slingshot%2C%20J.htmPotential Energy• Fuel is chemical potential energyhttp://www.alternativefuels.com.au/Biodiesel/dragster.htmhttp://www.lilligren.com/Redneck/redneck_lawnmower.htmGravitational potential energy• Due to object’s position• Relative to a surfaceGravitational potential energy= weight x height =• Work done for object to gain potential energymghGravitational potential energyGravitational potential energyEP= mass x acceleration of gravity x heightHeight is above some reference levelPotential energy is alwaysreferenced to a zero level defined in the systemGravitational potential energy•EP= mgh• mg = weight• h = heightGravitational potential energy•EP= mgh• Path to the height is not factor in EPGravitational potential energy•EP= mgh• Horizontal distance is not factor in EPWork, Power and Energy• How much work is done when you carry a 75 N bowling ball across the room?• Not any, no change in height, so no change in potential energyWork, Power and Energy• Potential energy only important when it changes• Change of EPdoes work•W=Fd•EPtransformed to another form of energyWork, Power and Energy•EPtransformed to another form of energy• Kinetic energy of motionWork, Power and EnergyWater behind the damPotential energyKinetic Energy of Motion•EK= ½ mv2• Work is a change in kinetic energy•W = ∆EK• ∆ Delta ‘change’Kinetic Energy of Motion•W = ∆EK• Work energy theorem•Net work • Due to net forceKinetic Energy of Motion• Heat• Sound• Electricity and lightConservation of Energy• Transformation from one form to another• Potential energy of stretched rubber of slingshot• Transformed to kinetic energy of rock flying through airConservation of Energy• Kinetic energy of rock flying through air = Potential energy of stretched rubber of slingshot• Transformed from potential to kineticConservation of Energy• Rock transfers its kinetic energy to the object it hits• May be transformed to heat upon impactConservation of Energy• Energy cannot be created or destroyed; it may be transformed form one form into another, but the total amount never changes.Conservation of Energy•EP= 10000 J EK= 0 J•EP= 7500 J EK= 2500 J•EP= 5000 J EK= 5000 J•EP= 2500 J EK= 7500 J•EP= 0 J EK= 10000 JConservation of Energy• http://science.howstuffworks.com/roller-coaster.htmConservation of Energy• Sun’s energy from fusion of hydrogen to helium• Sun’s energy converted to chemical energy by plants• Sun’s heat converted to potential energy when it evaporates waterenergyHeH +→42114Conservation of Energy• Does a car use more fuel when its lights are on?• What about when the air conditioner is on?• How about using the radio when the engine is
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