Work. Kinetic and Potential Energy. Work. Transference of Energy Work = Force x distance. Supplemental Text Material Pages

Transcription

1 Kinetic and Potential Energy Supplemental Text Material Page Tranference of Energy = Force x ditance Lifting load againt the force of the weight of the object Twice the ditance reult in twice the work Twice the weight i twice the work Twice the weight Twice the ditance Weight lifter expend energy to keep the potential energy in the barbell But he doe no work on the barbell after it i lifted

2 Unit of force = Newton = Force x ditance = Newton meter Unit of work are Joule i energy = kg m m = =Joule kg m Power Nothing about time in definition Slow or fat Same force, ame ditance = ame work Power = work / time Unit Joule/econd kg m / = 1 = = watt 3 3 Power P = energy/time = watt Half the time =Twice the power Twice the time =Half the power Power P = energy/time Fuel burn Biodieel

3 v. Energy Same unit occur with tranfer of energy occur when you tore potential energy Energy tored in bow i done to create the potential energy v. Energy v. Energy Lift heavy ram of pile driver tranfer energy to lift into potential gravitational energy v. Energy Mechanical energy Moving thing ha two form 1. Potential mechanical energy Waiting to work. Kinetic mechanical energy being done Potential Energy Potential Energy Fuel i chemical potential energy

4 Due to object poition Relative to a urface = weight x height = mgh done for object to gain potential energy E P = ma x acceleration of gravity x height Height i above ome reference level Potential energy i alway referenced to a zero level defined in the ytem E P = mgh mg = weight h = height E P = mgh Path to the height i not factor in E P

5 E P = mgh Horizontal ditance i not factor in E P, Power and Energy How much work i done when you carry a 75 N bowling ball acro the room? Not any, no change in height, o no change in potential energy, Power and Energy Potential energy only important when it change Change of E P doe work E P tranformed to another form of energy, Power and Energy E P tranformed to another form of energy Kinetic energy of motion, Power and Energy Water behind the dam Potential energy Kinetic Energy of Motion E K = ½ mv i a change in kinetic energy W = E K Delta change

6 Kinetic Energy of Motion W = E K energy theorem Net work Due to net force Kinetic Energy of Motion Heat Sound Electricity and light Conervation of Energy Tranformation from one form to another Potential energy of tretched rubber of linghot Tranformed to kinetic energy of rock flying through air Conervation of Energy Kinetic energy of rock flying through air = Potential energy of tretched rubber of linghot Tranformed from potential to kinetic Conervation of Energy Rock tranfer it kinetic energy to the object it hit May be tranformed to heat upon impact Conervation of Energy Energy cannot be created or detroyed; it may be tranformed form one form into another, but the total amount never change.

7 Conervation of Energy Conervation of Energy E P = J E K = 0 J E P = 7500 J E P = 5000 J E P = 500 J E P = 0 J E K = 500 J E K = 5000 J E K = 7500 J E K = J Conervation of Energy Sun energy from fuion of hydrogen to helium 1 4 H 4 1 He + energy Sun energy converted to chemical energy by plant Sun heat converted to potential energy when it evaporate water Conervation of Energy Doe a car ue more fuel when it light are on? What about when the air conditioner i on? How about uing the radio when the engine i off?