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Episode 47 - Entropy 0:00 1:44 2:04 3:30 4:30 6:45 7:50 9:35 10:00 11:42 12:40 13:12 14:00 14:40 16:45 17:30 20:00 Credits, etc. Intro Four postulates, laws of thermodynamics 2nd - entropy principle 1st - energy conservation 0th - temperature 3rd - absolute zero Deduce properties of matter Ultimate fate of universe Chalkey’s Billiard Room Investigate laws of thermodynamics Drinks with ice: beakers and experimental fluid T = 295 K alcohol and crystalline H20 @ 273K Ice cubes don’t melt at once: no warm ice cubes Ice melts as heat flows into it Why won’t it warm up? Why approach equilibrium? Clouds, volcano, iceberg formation, savannah, waterfall Earth is a machine, a factory never running down, driven by energy of sun Trade winds, ships: heat in motion sets matter into motion for both steam engine: heat TH TC TH - exploding gasoline TC - circulating cooling system TH, TC better engine TH = TC equilibrium, out of gas Molecular dynamics simulation Reaching thermal equilibrium Falling body bouncing: kinetic energy thermal energy Clouds U+K=Q Carnot cycle: Sodi Carnot - isotherm, adiabat Qin at Tin ; Qout at Tout ; W done Rudolf Clausing & William Thompson rescued Carnot’s writings efficiency, e = 1 Qout/Qin = 1 Tout/Tin Clausius - S = Q/T same in and out ideal engine conserves energy and entropy real engine Sout > Sin - entropy is created - not isothermal or adiabatic, there’s friction entropy flow S = Q/T (Question: why is entropy created in a real engine?) S 0 until everything is at equilibrium ice melting @ T = 0C Swater > Sice water more disordered ice melting - Sice > 0 (good) S rest of universe = E/T < 0 (not good) Suniverse > 0 strive to maximize SE/T i.e. minimize F = ETS (free energy) 24:45 heat death of universe 25:10 Goodstein entropy principle - flow of time atomic collisions are time-reversal invariant (S 0 doesn’t apply) ball bouncing - forward direction is one where successive bounces get smaller S > 0 same as t > 0 (tautology) no Episode 48 Low Temperature 32:18 33:27 Goodstein—cold changing air into liquid state dependent on temperature & pressure Faraday experimented w/ states of matter first to realize that matter can exist in 3 states, relationship of states to pressure & temperature states animation, phase diagram critical point—Le Tour—ethane demonstration evaporation & condensation August 1950 again evaporation animation Da Vinci—system to cool air Goodstein—carbon dioxide as coolant Faraday—liquefied every known gas but oxygen, nitrogen, & hydrogen cascade process heat exchanger animation Joule & Kelvin Joule-Thomson effect animation Linde—final step in liquefying air liquid hydrogen Royal Institution Netherlands—University of Leyden race to liquefy hydrogen Kamerlingh Onnes vs. Dewar Dewar won, but helium discovered just before, so hydrogen no longer last known gas to be liquefied Kamerlingh Onnes—first to liquefy helium @ 4 K Goodstein—liquid air 35:56 37:55 41:12 42:28 43:41 44:13 46:22 48:00 49:12 49:59 50:49 52:15 55:48