2013-3-1 Power Power the rate of energy transfer by work W=F.V -force time velocity And the total work can be calculated as W=wdt= F.Vdt NOTE:Dot over a symbol indicates time rate SI units:J/s watt (W) English units:ft-Ibf/s,BTU/h and hp (horsepower） 2-29 Energy Transfer by HEAT Heat is the form of energy that is transferred by virtue of temperature difference between the system and its surroundings(or two systems). Net energy transfer by heat occurs only in the direction of decreasing temperature. Gas Container on hot plate: Energy is increased but no Gas work is done! Hot plate 2-30 152013-3-1 15 Power 2-29 Power = the rate of energy transfer by work - force time velocity And the total work can be calculated as NOTE: Dot over a symbol indicates time rate SI units: J/s = watt (W) English units: ft·lbf/s, BTU/h and hp (horsepower) Energy Transfer by HEAT 2-30 ►Heat is the form of energy that is transferred by virtue of temperature difference between the system and its surroundings(or two systems). ►Net energy transfer by heat occurs only in the direction of decreasing temperature. Gas Container on hot plate: Energy is increased but no work is done!