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Chapter 16Thermal Energy and HeatPhysical Science

Thermal Energy and Matter 16.1In 1700s, scientist thought heat was fluid called caloricNot fluid or state of matter but related to motionWork and HeatHeat transfer of thermal E from one object to another bc of temp differenceFlow from hot to coldCan occur bc of friction from workTemperatureMeasure of how hot or cold bc of movement of particleaverage kinetic E of the particles in an object due to random motionall particle collisions transfer thermal E

The particles inside an ice cube are moving very slowly. The particles in boiling water are moving very fast.

Thermal Energy 16.1Total potential and kinetic E of all the particlesDepends on:MassCup of hot tea vs. teaspoon of hot teaSame temp = so same average kinetic energyCup tea more thermal E b/c more particlesTemperature Cup of hot tea vs. cup of cold teaSame mass, same # of particlesDifferent average kinetic E = energy of particle higher in hot tea = greater thermal EPhase (solid, liquid, gas)Phase changes transfer thermal energy

Thermal Contraction and Expansion 16.1Thermal Expansion increase in volume of material bc of temp increase particles move faster collide more often expandGases expand more than liquids, liquids more than solidsbc force of attraction is lessThermal ContractionTemperature decreases particles move more slowly collide less oftenSpecific Heat 16.1Amount of heat needed to raise the temperature of 1 gram of a material by 1 degreeLower specific heat = heat fasterJoules per gram per degree CelsiusQ = m(c)(T)

Measuring Heat Change 16.1Calorimeter instrument used to measure changes in thermal EUsed to measure specific heat of Al

Math Practice # 1- 5 Page 477

Heat and Thermodynamics 16.2Conduction transfer of thermal ENot transfer of matterMaterials are TOUCHINGSlower in gases than liquids, liquids slower than solidsbc of particle locationFaster in metals bc electrons free to move (sea of e-)Thermal Conductors material that conducts wellMetalDoes not have to be hot tile floor colder than wooden floor bc tile is a better conductor and transfers thermal E quickly to skinThermal Insulator material that conducts poorlyWood, air, plastic, foam

Convection 16.2Transfer of thermal energy when particles of a fluid (liquid or gas) move from place to placeHot to coldConvection current- fluid circulate in a loop as it alternately heats up and cools downOccurs in oceans, weather, and movement of hot rock in Earths interior Ovens

Radiation 16.2Transfer of E by waves moving thru spaceAll objects radiate energyAs temp increases, radiation increases

Thermodynamics 16.2The study of conversions between thermal energy and other forms of energy1st Law energy is neither created or destroyed2nd Law thermal E can flow from colder to hotter objects only when work is doneRelates to entropy (disorganization of system)Heat engines converts heat into workEfficiency is always less than 100%Waste heat = thermal E not converted to workSpontaneous changes makes system less orderly unless work is doneWorld is always becoming less orderly3rd Law absolute zero (O K) cannot be reachedSolar Homeshttp://www.youtube.com/my_playlists?pi=0&ps=20&sf=&sa=0&sq=&dm=0&p=CB817BBF0B24D9CA3 clips = 4 minutes

Heat Engines 16.3External Combustion Engine an engine that burns fuel outside the engine1st used to pump water out of coal minesHot steam enters in right valve slide to left steam trapped expands and pushes piston heat converted to workAn External Combustion Engine

Figure 11

An External Combustion Engine

Figure 11

An External Combustion Engine

Figure 11

Heat Engines 16.3Internal Combustion Engines Fuel burns inside the engineMost use pistons that move in a cylinderEach motion up and down = strokeLinear motion is converted to rotary motion by crankshaftCrankshaft = connected to transmission (linked to wheels and driveshafthttp://www.youtube.com/my_playlists6 minAn Internal Combustion Engine

Figure 12Heating System 16.3Central heating system heats many rooms from 1 central locationCommonly used electrical energy, natural gas, oil, and coalDiffer in how they transfer thermal energyHot-Water HeatCirculating pump carries hot water to radiators in each room conduction (water to radiator) conduction and radiation (heating room) convection in roomSteam HeatingSimilar to hot water heat but use steam insteadOften used in older buildingsElectric Baseboard HeatingUse electric energy (convert electrical to thermal)Hot coils heat air by conduction and radiations convection causes circulationSpace heaters are similarForced-Air HeatingUse fans to circulate air thru ducts to rooms convection circulates air in roomb/c warm air rises, warm-air vents are located in floorAdvantage = air is cleaned as pass thru filters

Cooling Systems 16.3Heat pump device that reverses the normal flow of thermal heatRefrigerant fluid that vaporizes and condenses inside the tubing of a heat pumpAbsorbs heat vaporizes turns into gasGives off heat condenses turns into liquidHeat pump must do work to refrigerant to reverse flowRefrigerators- heap pump that transfers thermal E from cold food compartment to warm roomOpen door adds more heat to room than it removes b/c coils get hotterAir ConditionerMust do work

http://www.expertvillage.com/video/165820_do-refrigerators-work.htm2 minutes