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Today 1 20 06 Frustrated that MP doesn t like the answer you think is correct Don t keep entering the same answer over and over Log out and email me babbitt teaching physics montana edu Homework HW 1 at end of last lecture Due Wednesday 1 25 before class Homework turn in box in Physics atrium don t confuse with lab box MP 4 will be at Mastering Physics by midnight Due next class Read through section 20 7 by 1 23 Practice problems from Serway Not to be turned in Problems 20 4 20 6 Assessment of past skills 20 minutes at end of class counts as in class activity Lab Manual Reading Read Introduction Lab 1 Specific Heat and Appendix A by 1 23 Pre Lab due before lab on Tuesday 1 24 we ll discuss on Monday Topics to cover today Heat and Internal energy Mechanical Equivalent of Heat Specific Heat Latent Heat Heat and Internal Energy Internal Energy is ALL the energy in a system at rest Doesn t include Bulk kinetic energy Gravitational potential energy Does include Bond energy Thermal energy Measured in Joules Pre lab You must do the pre lab BEFORE you get to lab In appendix A don t worry too much about confidence levels Do pre lab on a separate piece of paper All other lab work goes into lab book You must bring a lab book to first lab Also bring a black or blue pen Assigned Pre lab for Specific Heat Lab part 3 of pre lab If you last name begins with the letter A C do a D G do b H J do c K M do d M R do e S Z do f Mechanical Equivalent of Heat James Prescott Joule s experiment 1843 Specific Heat of Water 1 cal g C 4186 J kg K 15 C Mass Frictionless Pulleys T Insulated Vessel Heat is the transfer of energy in or out of system due to a T That is not to say you can t change T without heat Nor must T change when a system is heated M Water mw Work and Heat both refer to the transfer of energy in and out of a system Work on a system and Heat flowing into a system are positive if they add energy to the system Work done by a system and Heat flowing out of a system are positive if they reduce the energy of the system Capacity Which has more load capacity What is load capacity A Ford 1 2 ton pick up My Ford Escort h Heat Capacity C High heat capacity is the ability of an object to absorb energy with little temperature rise More heat capacity Less temperature rise for given energy input The change in temperature is proportional to energy transfered High load capacity of a vehicle is the ability to carry lots of weight with little deflection of the suspension system More load capacity Less crushing for equal loads T Ein C where Ein is energy input Positive energy input rise in temperature Energy leaving negative energy input drop in temperature 1 Heat Capacity and Specific Heat Specific Heat Example Heat Capacity C of object Depends on the type of material the object is made of Is proportional to the mass of object Specific Heat c is the proportionality constant C m c A hunk of Aluminum is added to volume of water at room temperature T Insulated Vessel Work and Heat transfer of energy in and out of a system The energy transferred by heat to an object that rises by T is The heat Q m c T The energy transferred by work to an object that rises by T is The work W m c T Aluminum mAl Water mw Remember Work on a system and Heat flowing into a system are positive if they add energy to the system Work done by a system and Heat flowing out of a system are positive if they reduce the energy of the system Calorimetry The Heat Capacity of Large Objects Latent Heat Let s put a candle under a chuck of really cold 30 C ice and watch what happens Ice Ice water Water Water Steam Steam I TRIPLE DOG DARE YA Time Latent Heat Latent Heat of Phase Changes It takes energy for an object to go From solid to liquid at the melting point Latent Heat of fusion From liquid to gas at the boiling point Latent Heat of vaporization Steam Why latent hidden T Ice Water Water Steam Ice water Latent Heat of Fusion Lf Energy per unit mass to go from solid to liquid at melting point Latent Heat of Solidification Ls Energy per unit mass to go from liquid to solid Equal to latent heat of fusion Total energy transferred for a mass m Q m Lf Latent Heat of Vaporization Lv Energy per kg to go from liquid to gas at boiling point Latent Heat of condensation Lc Energy per unit mass to go from gas to liquid Equal to latent heat of vaporization Total energy transferred for a mass m Q m Lv Why latent hidden Typically Lv Lf Energy Added Joules 2 Internal Energy of System Latent Heat of Fusion and Vaporization Steam Heating 0 1 kg of 30 C ice to 130 C steam T Ice Ice Ice water Water Steam c a Water Steam Water e b Steam T Water d Change in Internal Energy Energy Added Joules a Ice from 30 C to 0 C Specific heat of ice ci 2090 J kg C Ice water b Ice 0 C to water 0 C Latent Heat of Fusion of water Lf 3 33x105 J kg c Water from 0 C to 100 C Specific heat of water cw 4186 J kg C d Water 100 C to steam 100 C Latent Heat of Vaporization of water Energy Added Joules Lv 2 26x106 J kg e Steam heated from 100 C to 130 C Specific heat of steam cs 2010 J kg C Latent Heat of Condensation and Solidification Example The Recipe for Ice Water The caf owner s most loyal customer wanted large glass of very cold water to slurp down while he quickly snorfed down his meal Cooling 0 1 kg of 130 C steam to 30 C ice The caf owner wanted to keep his customer satisfied by providing lots of ice cold water but also wanted to save on ice Too much ice Less water in cup and wasted ice Customer would ask for more water during meal Too little ice Water not at 0 C Customer would complain it wasn t cold enough Steam T a Water Steam Water b c Ice water Lc Lv d Ice Ls Lf The caf tap water is typically 20 C 68 F The caf freezer is set to 20 C 4 F e What is the perfect recipe the caf owner should follow for making ice water for his favorite customer Energy Released Joules 3


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