[Music] [Applause] [Music] somewhere around 1800 there was an extraordinary Frenchman whose name was Lazar carau he was a Statesman and a minister in various French governments and in fact he was so effective that he was known as the organizer of victory of the French Wars of Revolution he was also a scientist and an engineer whose work was important enough that it's remembered even today this glorious family tradition was carried on almost a century later by sad Carno another engineer who became president of the Republic of France in 1887 a position he held until 1894 when he was assassinated but the most important of the Kos was neither of these he was instead one who came between them his name was Nicholas Leonard sad cono called by everyone sad and that cono was interested in Steam Engines [Music] from England's fits and starts in the early 1700s to the non-stop promise of the American frontier nothing expanded the Vista of Western Civilization wider and farther than the invention of the steam engine many saw the coming machines as a threat coughing sputtering disturbing the peace and upsetting the status quo the machine was viewed as a nasty little nuisance of an idea but once given birth it was here to [Music] stay steam Rose in the Industrial Age and grew up into the power behind the revolution with growing acceptance on both sides of the Atlantic and in as many clever configurations as Engineers could devise steam engines began to turn dreams into [Music] realities steam engines turned the Looms of the cotton Bel and wo the the fabric of a Nation the steam engine cut and shaped the wood drove the Pistons and pulled the levers the steam engine churned the butter and ground the corn and turned the small family business into an international concern with steam the groundwork was laid and the sleeves of an industrial giant were rolled up to [Music] stay the power of the steam engine was energy and movement and change it became a symbol of opportunity whether that men had escaped from the Potato Famine from the wages of slavery or from the Russian zar the steam engine saved time and labor and indeed for all its upheaval and inequity the steam engine offered the promise of a steady wage every quota was to bring more of everything everything faster and better and easier and Cheaper by the [Music] Dozen out as far as men could lay track wherever one looked it looked as if the nation's most important product was progress and yet as far as the steam engine carried the body and soul it carried man's intellect even further full soon Lord Byron wrote steam engines will conduct him to the [Music] Moon the inside of the poet Byron was on the right track but the steam engine goes above and beyond the moon as an idea it goes so far as to raise questions about the very meaning of time and about the ultimate fate of the universe itself that was the journey that began in the mind of sad Carno born in 1796 carau may have inherited his aptitude for mathematics and Military engineering from his father Lazar who in reward for his skills in organization and tactics had become a hero of the French Revolutionary Wars with his father's influence carau entered the aold PO technique young Carno discovered both the steam engine and the fact that his country lagged behind in its development for a military entity like France this was a problem but for a military engineer it was a challenge but rather than building a better steam engine young Carno came up with a better theory of course steam power was by no means a new idea starting with Thomas savory's steam-driven water pump in 1698 inventors and Engineers such as Thomas newom Richard trebic Matthew Bolton and of course James Watt had been refining the steam engine making it better more powerful and most important more efficient one after another ingenious devices for squeezing just a little more work out of a ton of coal came forth from the minds of inventors but it was above all James watt's discovery of a way to cool the steam outside the main cylinder using a condenser that really got the era of the steam engine [Music] underway but when it comes right down to the steam engine what's really essential of all the valves and gears of all the beams and pipes of all the gadgets and gauges of all the engines with all their bells and whistles and whatever works to catch the buyer's fancy what is the very essence of the engine it's the cylinder a cylinder with a movable end pushed by pressurized Steam opening a valve to the boiler admits High Press steam that pushes the Piston out doing work on the flywheel the flywheel pushes the Piston back in again expelling the spent steam through another valve and the engine is ready for the next cycle and so it goes in and out in and out no matter the purpose or design the cylinder is the key and everything else is bells and whistles and with the very essence of the steam engine in mind Sadi Carno asked not how can I make it a little better but what is the absolutely most efficient steam engine that nature will allow looking for the answer sad carau found his inspiration in the water wheel of course the steam engine wasn't the first invention to ease the burdens of physical labor since ancient times Beasts did their share of plowing and Milling of pumping irrigation water and carrying the crops to Market but as a step away from agrarian culture and toward the Industrial Revolution and its own beastly machines the water wheel not the steam engine came [Music] first and as water powered the Looms of the British textile industry other fluids began making the rounds in the most scholarly Circles of the day the scientific World regrouping in the wake of Sir Isaac Newton had begun to realize that not all natural phenomena were explained in the principia for a while the idea of a variety of mysterious fluids became a popular solution for any number of physical puzzles electricity for example the solution to the problem of electricity was a fluid that flowed from the subtle mind of Benjamin Franklin and meanwhile back on the continent Joseph Priestley tried to solve the problem of combustion fire itself and the related problem of metals rusting Priestly was a chemist and his solution of course was a fluid flist a subtle weightless fluid that like electricity combined with ordinary matter to make metals and escaped when metals rusted another problem was heat which for all practical purposes flowed like a liquid from one body to another to a century already a wash in fluids a heat fluid called caloric was comparatively easy to invent but there was one fluid that needed no inventing at all even as sad Carno struggled to understand the infernal power of steam the countryside abounded with examples of water power just as a water wheel is run by water the flow of water from a high plane to a lower plane a steam engine he thought is run by the flow of caloric from high temperature to low temperature with this simple but Vivid picture in mind Young Sad carau had found the key to Nature's limit on how efficient a steam engine could be no machine or combination of machines can ever have the effect of making more heat run up to high temperature than down to low temperature that idea was the starting point of carno's theory and even to this day it's one of the basic foundations of physics of course now it's called the second law of Thermodynamics Carno realized is that a water wheel running backwards could be used to lift water uphill in fact he could even imagine one water wheel driving another in Reverse Falling Water on one side being used to raise water on the other but he knew that the combined machine could never raise more water uphill than was flowing downhill applied to the flow of heat instead of water that principle became the second law of Thermodynamics with this Insight carau knew that the best engine nature would allow was one that could run equally well backwards and forwards in other words an engine that could take Heat at low temperature and raise it to high temperature in an ordinary engine higher temperature heat Flows In work is done and heat flows back out at low [Music] temperature Carno imagined an engine that could work in Reverse heat would flow in at low temperature with the help of work supplied from outside and heat would be deposited at high [Music] temperature there's a name for a machine that works that way it's called a refrigerator a refrigerator with the help of a motor removes heat where it's already cold and deposits Heat at higher temperature outside of itself the idea is not uncommon today but in the 1820s Carno had a special challenge how to design a steam engine that could work equally well as a refrigerator caros started by reducing the engine to its Essentials no boiler no flywheel no valves he did need a cylinder and a movable piston but he could even do without steam because the cylinder could be filled with [Music] air heat it and the air expands driving the Piston outward cool it and the air contracts making it easy to push the Piston back [Music] in heat flows in at high temperature and the Piston does work [Music] as the cylinder cools it takes work to push the piston in but since it's cooler the air inside exerts less pressure so it takes less work so there's some net work gain by the machine so there it is the essential engine heat energy goes in and less heat energy comes out and the difference comes out as you for [Music] work the essential engine shares the most important features of all real [Music] engines heat goes in work gets done and heat must always be expelled at lower temperature to make the engine ready for the next stroke but there is a problem heat flows easily from a hot Source into a cold cylinder or from a hot cylinder into a cold Source but those are steps that can never run in [Music] reverse because they would require heat to run the wrong way carno's ideal engine that works equally well backwards as forwards could not make use of those two strokes to make a reversible stroke the cylinder would have to be hot before the heat runs [Music] in allow the hot gas to expand and more heat flows in doing work push the Piston back in and heat flows the other way that's a reversible stroke it takes place at constant temperature so it's called isothermal heat goes in the gas expands end and work is done next a brilliant stroke isolated from the heat Source the gas is allowed to expand further doing more work since there's no external source of heat it comes from the internal energy of the gas itself causing it to cool this step is also reversible and it's called adiabatic now the cylinder is ready for another isothermal step this time using up some work to expel Heat at low temperature finally an adiabatic squeeze warms the gas getting it back to the starting point ready for another [Music] cycle on each cycle some net work is done just as in a real engine but each of these steps Works equally well running backwards so the Carno cycle is both an engine and a refrigerator working equally well in both directions a perfectly reversible [Music] machine of course carno's engine works perfectly only in the imagination but it has a lot in common with a real engine for example like a real steam engine the Carno engine uses a source of heat at high temperature and like a real one it also needs a place to release Heat at a lower temperature and the cylinder where gases can expand and contract but just about there the similarities end and the real challenge begins how could Carno prove that his was the most efficient engine possible the answer may be found by comparing a real Engine with the carau [Music] engine burning fuel produces an amount of heat Q subi at high temperature T subi put that heat into the Carno engine and it does work W the efficiency of the engine is just the work out divided by the heat in but could a real engine ever be more efficient than a Carno engine in other words requiring less heat in Q subir to produce the same amount of work if so that work could be used to make the Carno engine run backwards if the real engine were connected to the Carno engine the effect would be much the same as carno's hypothetical water wheels the real machine takes in heat and does work which is the exact amount of work the Carno engine needs to run backwards remember if the real engine were more efficient Q subir would be be smaller than Q subi so when the two engines are connected they have the net effect of making heat run uphill but that violates the second law of Thermodynamics if the second law of Thermodynamics is correct the real engine can't be more efficient than a carau operating by means of heat flowing from a given high temperature to a given low temperature the Carno engine is always more efficient than a real engine and and since the second law of Thermodynamics is correct the Carno engine is the most efficient engine that mother nature allows sad Carno began with a brilliant analogy the water wheel and concluded with the essence of an engine the most efficient engine possible between two temperatures but carno's analogy wasn't entirely correct unlike water in a wheel heat doesn't merely flow through an an engine some of the engine's heat gets used up and actually turns into work which means that considering the law of the conservation of energy it's very easy to ask carno's question and come up with the wrong answer for example if an engine uses heat to produce work then the most efficient engine would seem to be one that turns all heat into work but that's the wrong answer even before the law of the conservation of energy Carno realized that some heat must flow out of any engine at low temperature that was the point of Watts condenser and the reason every car needs an efficient cooling [Music] system according to the law of the conservation of energy the work done is simply the difference between the Heat in and the heat out and so the efficiency of any engine is always less than one carno's original logic was so precise that it remained valid even with the discovery of the conservation of energy no engine not even a car no engine can reach the goal of perfect efficiency but then how efficient can a Carno engine be it depends on the temperature the hotter the high temperature and the cooler the low temperature the more efficient an engine will [Music] be in fact later generations would discover that for a Carno engine Q subo over Q subi is equal to T subo over T sub I and that's the most efficient an engine can be s Carno Died In 1832 he was only 36 years old he died tragically in his youth of scarlet fever during his own lifetime he was not really famous he was respected but he was after all an engineer an engineer's job is to build better machines and Caro's ideas clever as they were helped no one to build a better machine so although he was a respect engineer nobody could get really steamed up about what he had done when jel came along and discovered the conservation of energy or establish the conservation of energy situ the situation for carau uh got even worse because after all his reasoning was based on a faulty foundation of the old caloric Theory but a German physicist by the name of Rudolph clausius came along at that point and rescued Caro's ideas what clausius had shown was that in this engine not in any engine but in an ideal perfect engine there is something which is the same going in as it is coming out it's something is conserved in an ideal engine that's something is not energy it's not the conservation of energy but rather the ratio of the energy in or heat in to the temperature at which it goes in and clausius gave a name to that conserved quantity ideally conserved quantity sometimes conserved quantity he called it entropy so if I had to summarize very briefly the history of the steam engine I would say something like this James Watt whose purpose it was to make money invented a more efficient steam engine and sad cono whose purpose it was to invent a more efficient steam engine changed our entire view of the universe because our view of the fate of the universe is based on the principle that came out of clausius analysis of Caro's work the principle of entropy and the principle of entropy is our subject for next time see you then [Music] is [Laughter] [Music] [Music] annenburg media for information about this and other anenberg media programs call 1 1800 learner and visit us at www.learner.org