12/8/10 1 Physics 12112/8/10 2 Physics 12112/8/10 4 Physics 12112/8/10 5 Physics 12112/8/10 6 Physics 121 T = ZZ =LA12/8/10 7 Physics 121 =Ak =1 T = Z =LA =Lk A T = R Thermal conductance Heat flow per unit area Thermal resistance (R-value)12/8/10 8 Physics 121Material k (W/m-C) Material k (W/m-C) Steel 12-45 Wood 0.4 Aluminum 200 Insulation 0.04 Copper 380 Air 0.025 12/8/10 9 Physics 12112/8/10 10 Physics 12112/8/10 11 Physics 12112/8/10 12 Physics 12112/8/10 13 Physics 12112/8/10 14 Physics 121 Average force of gas on the wall = (# of molecules hitting the wall in the time t) x (force each molecule exerts on the wall) Fwall molecule= mvxt= Fmolecule wallOnly the x-component matters. All we need to figure this out is our three basic equations, and a way to count the number of molecules hitting the wall. vx=xtA vxt12/8/10 15 Physics 121 N = n Volume()= nA vxt()px= 2mvxn = number density = # / unit volume12/8/10 16 Physics 121 v = vx2+ vy2+ vz2= 3 vx2vx= v /312/8/10 17 Physics 121 F = Npt=12(nAvxt)2mvxt = nmvx2AInterpret F = pA n =NVvx2=13v2pA =13NVmv2ApV = N(13mv2) = N2312mv2()12/8/10 18 Physics 12112/8/10 19 Physics 121 pV = nmolesRT12/8/10 20 Physics 121 N = nmolesNA12/8/10 21 Physics 121 pV = N23(12mv2) pV = nRTMake the N parts look alike.n = N / NApV = NRNA TDefine: kB=RNA so pV = NkBT12/8/10 22 Physics 121 p = Nmvx2kBT
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