Judah Levine, 3070L2 1http://physics.colorado.edu/phys3070http://physics.colorado.edu/phys3070Judah LevineJudah LevineJILA SJILA [email protected]@colorado.edu303 492303 492--7785 (27785 (2--7785)7785)M,F 11M,F 11--Noon, W 1Noon, W 1--3 pm3 pmalso by appointmentalso by appointmentJudah Levine, 3070L2 2Question to test the clickersQuestion to test the clickersQQWhat was the color of George What was the color of George WashingtonWashington’’s white horse?s white horse?A: RedA: RedB: WhiteB: WhiteC: BlueC: BlueD: GreenD: GreenE: PurpleE: PurpleJudah Levine, 3070L2 3971608402103.2)101.7()105.3(××××The value of this expression is:A: 40×10108B: 1.08×1040C: 23.5×1040D: 10.8×1041E: None of theseJudah Levine, 3070L2 4971608402103.2)101.7()105.3(××××The value of this expression is:40399716084021008.1108.10103.21.75.3×=×=××−+The correct choice is BJudah Levine, 3070L2 5Units of work and energyUnits of work and energyQQMechanical Units: Force Mechanical Units: Force ××DistanceDistance––FootFoot--poundpound––NewtonNewton--meter = joulemeter = jouleQQRotation:Rotation:––Torque Torque ××AngleAngleJudah Levine, 3070L2 6Units of work and energy Units of work and energy --22QQHeat/temperature unitsHeat/temperature units––caloriecalorie••Change temperature of 1 gm of water by 1Change temperature of 1 gm of water by 1°°CC––Calorie (or kiloCalorie (or kilo--calorie)calorie)••Change temperature of 1 kg of water by 1Change temperature of 1 kg of water by 1°°CC••1 jelly donut = 250 Calories1 jelly donut = 250 Calories––British Thermal Unit (BTU)British Thermal Unit (BTU)••Change temperature of 1 pound of water by Change temperature of 1 pound of water by 11°°FFJudah Levine, 3070L2 7Clicker QuestionClicker QuestionQQAbout how many BTUs are needed to About how many BTUs are needed to boil water from room temperature to boil water from room temperature to make 1 cup of tea?make 1 cup of tea?A: about 7A: about 7B: about 25B: about 25C: about 70C: about 70D: about 200D: about 200E: about 1000E: about 1000Judah Levine, 3070L2 8Clicker QuestionClicker QuestionQQAbout how many BTUs are needed to About how many BTUs are needed to make 1 cup of tea?make 1 cup of tea?Cup of water is about ½ poundTemperature increase from 75F to 212F= 137FBTUs= ½×137=68.5 The correct choice is CJudah Levine, 3070L2 9Role of Energy in PhysicsRole of Energy in PhysicsQQPrinciple of the conservation of EnergyPrinciple of the conservation of Energy––Work results in a change in energyWork results in a change in energy––Conversion of energyConversion of energy––(mass(mass--energy equivalence)energy equivalence)QQEfficiencyEfficiencyQQNo time dependenceNo time dependenceJudah Levine, 3070L2 10PowerPowerQQPower is Energy/TimePower is Energy/Time––1 joule/second = 1 watt1 joule/second = 1 watt––footfoot--pound/secondpound/second••550 ft550 ft--lbs/sec = 1 horsepowerlbs/sec = 1 horsepower––BTU/hrBTU/hr••Gas appliances, furnaces, Gas appliances, furnaces, ……––BTU/yearBTU/year••National and world energy consumptionNational and world energy consumptionJudah Levine, 3070L2 11PowerPowerQQPower is Energy/TimePower is Energy/Time––1 joule/second = 1 watt1 joule/second = 1 watt––footfoot--pound/secondpound/second••550 ft550 ft--lbs/sec = 1 horsepowerlbs/sec = 1 horsepower––BTU/hrBTU/hr••Gas appliances, furnaces, Gas appliances, furnaces, ……QQEnergy is PowerEnergy is Power××TimeTime––1 watt1 watt--hour= 3600 watthour= 3600 watt--seconds=3600 jouleseconds=3600 joule––1 1 kwhkwh=3600=3600××101033joules= 3.6joules= 3.6××101066joulesjoulesJudah Levine, 3070L2 12Power vs. EnergyPower vs. EnergyQQEnergy is a fundamental physical Energy is a fundamental physical parameterparameterQQPower is often more relevant to Power is often more relevant to everyday lifeeveryday lifeJudah Levine, 3070L2 13Types of Energy Types of Energy ----11QQKinetic Energy Kinetic Energy ––the the energy of motionenergy of motionjoulesmvKE 905.180212122=××==m in kilograms, v in m/senergy in joulescannot use m in
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