First Law of Thermodynamics: History of the Concept of Energy

– We’d like to begin in the early 1700s with a remarkable woman named Emilie du Chatelet Emilie was born in 1706 and she was the only daughter of a wealthy and connected French family She was brilliant in mathematics and languages from an early age Her father lamented quote, “my youngest flaunts her mind “and frightens away all the suitors “We just don’t know what to do with her.” Her father was exaggerating, of course, because with beauty, money and high social status, there are plenty of men who are willing to look past her unusual intelligence When she turned 18, she decided she didn’t want to be forced to live in a convent, like most unmarried upper-class women were at the time and agree to an arranged marriage to 34 year old marquee They had three children in quick succession and afterwards had what can only be described as an open marriage In 1733, Emilie met the poet Voltaire and they immediately fell in love Voltaire was always in trouble with the French government, for pushing for freedom of religion and speech and satirizing the religious and secular leaders of the day In fact, when he met Emilie, he was still a little bit in trouble, having just returned from exile in England, where he learned about Newton’s philosophies Soon, Emilie, her husband and her lover Voltaire decided to hole up at her country home called Cirey Emilie wrote a friend quote, “there is heroism or perhaps madness “in my shutting myself up at Cirey with the three of us.” Emilie du Chatelet and Voltaire then created an Academy of sciences with over 21,000 books, larger than most universities at the time In 1738, they started to collaborate on a book on Newton where Emilie did most of the math and Voltaire wrote most of the pros or as he put it to a friend, “Madame du Chatelet had her part in the work “and that she dictated and I wrote.” Of course, all of Emilie du Chatelet’s work did not induce Voltaire to include her name in the title Although he did dedicate it to her and put her topless image inside the cover as an angel After the publication of that book, Voltaire started to work on a competition about the nature of fire and light, which Emilie du Chatelet thought was dead wrong Frustrated with Voltaire, ignoring her ideas, Emilie secretly wrote her own paper She determined that if a ray of light had any mass at all, then the speed of light would mean that quote, an instant of light would quote, destroy all the universe and therefore light must have no mass Emilie du Chatelet also decided that fire ie. heat was quote, the cause of the internal motion of the particles of all bodies And she even predicted the third law of thermodynamics 200 years before Walther Nernst saying it was impossible that had a particle that was in quote “perfect repose.” And that quote, “all in nature is in perpetual oscillations “of dilation and contraction caused by the action of fire.” Neither Voltaire nor Emilie du Chatelet won the contest nor even got honorable mention But her reputation as a serious scientist was made Her gossipy neighbor wrote “I read the dissertation on fire that Madame wrote “It is so clear, so precise “I apologize to Monsieur Du Voltaire, “but it’s much better than his.” And when did she write this discourse? At night, because she was hiding from Voltaire While researching how destructive sunlight could be, if it had mass, she started to study what different scientists said about the destructive effect of moving objects with mass And having just written a book on Newton, she was up to date on Newton’s theories However, despite what I was told in school, Newton never wrote the force equals mass times acceleration In fact, the closest he ever came to it was quote, “a change in motion is proportional “to motive force impressed.” Instead Newton, and the French scientists, Descartes were much more focused on the mass times the speed, as if two objects collide with identical mass times speed and stuck to each other, they would stop moving And for this reason, some people started to call mass times speed, the dead force, Emilie Du Chatelet wasn’t limited to Newton or Descartes See at the time, science was a bit of a nationalistic pastime If you were English, you need to support Newton If you were German, Leibniz, if you were French, Descartes Often to the exclusion of other Emilie thought this was ridiculous and wrote about a book of physics, one must ask if it is good, not if the author is English, German or French, or as Voltaire put it, quote, “in the kingdom of Madame du Chatelet, “there is an absolute freedom of conscience.” In 1738 or so, Emilie du Chatelet

learned that Newton’s rival, Gotfried Leibniz, had proposed something that he called living force that was dependent on the mass times velocity squared, which was conserved when objects bounced off each other, living because this quote unquote, force was only conserved for moving objects Newton and Leibniz were enemies from their days where they argued about who discovered calculus and almost everyone in Europe was firmly in one camp or the other However, Emilie felt differently telling her son, quote, “do not carry respect for the greatest men “to the point of idolatry “No book is so good that one might not improve it. ” Now, one of the definitive experiments that convinced Emilie du Chatelet that the damage of a moving object depended on the speed squared times the mass or the living force is dramatized by the 2005 documentary, “Einstein’s Big Idea.” – Gotfried Leibniz has been dropping lead balls into a pile of clay – Dropping lead balls into clay, how very imaginative – Using Newton’s formulas, Monsieur Voltaire, he then drops a second ball from a higher height calculated to exactly double the speed of the first ball on impact So Monsieur care for a little wager? Newton tells us that by doubling the speed of the ball, we will double the distance it travels into the clay Leibniz asks us to square that speed If he is correct, the ball will travel not two but four times as far So who is correct? – Monsieur, I feel Mr. Newton’s reputation dwindling ever so slightly – Tweed and not succumb to that There is no earthly reason to ascribe hidden forces to this Dutchman’s lead ball. (laughs) – Well, the ball travels four times further – Anyway, in 1740 Emilie du Chatelet published a book called Lessons in Physics, which was the first to champion Newton’s theories and the idea of the living force and help promote both Newtons and Leibniz’s theories in France, Germany, and even England Du Chatelet continued to research science And in 1747, she completed her Magnum Opus, the first and still gold standard French translation of Newton’s Principia with footnotes about the living force Tragically, she died just before its publication at age 42 from complications from childbirth After her death, Emilie du Chatelet’s ideas about Newton, Leibniz, fire, light, philosophy and living forces were all reproduced Sometimes plagiarized word for word by her friend, Diderot, in the very influential French encyclopedia Her influence was obscured by her death, but her scientific ideas flourished Fast forward to England in 1807 That was when a doctor and scientist named Thomas Young, who is famous for his double slit experiment from a few years earlier, that demonstrated that light acts like a wave was asked to give a series of lectures on the current state of science Young decided to make his lectures as simple as possible because he wanted to dedicate it to the women in the audience, specifically because he felt the upper class women would be better served if they spent their time in the quote “acquisition of knowledge, instead of wasting their time, “then sip it consumption of superfluous time.” Anyway, in his fifth lecture, out of 60, he decided to rename the living force or the mass times speed squared saying that quote, “the living force is somewhat more “concisely expressed by the term energy.” His lectures were published as a book and soon has simplified physics for the ladies caught on in England and the term energy was used instead of living force, at least in England Now we go back to France and two ex soldiers, Sadi Carnot and Gasbard-Gustave Coriolis who were interested in the efficiency of machines As Carnot put it, quote, “the study of engines is of the greatest interest “as their importance is enormous “And they seem destined to produce “a great revolution in the civilized world.” Both men were the children of generals and both men in the early 1800s went to the same school to study engineering for military officers However, Sadi Carnot started in a much better position in French society as he was the son of one of Napoleon’s top captains and Coriolis was the son of the former King’s top captains and King Louis that said had been decapitated when Coriolis was just an infant They switched social positions in 1815 when Napoleon was defeated and Carnot’s father was exiled Sadi Carnot was allowed to remain in France,

but he found military life very frustrating without any political power And in 1818, Carnot left the military and holed up in his brother’s apartment in Paris, secretively studying science Carnot wouldn’t even tell his brother what he was working on Meanwhile, Coriolis’ father died and Coriolis left the military So that he can make a little bit more money as a scientist, studying engineering systems As a former engineer, he had a lot more technical experience with actual engines than the typical academic In 1829, Coriolis published a book on the physics of machines In this book, Coriolis defined a new term that he called work, that he defined as the force times the distance and the direction of motion Surprisingly, this is still the modern physics definition of work Moreover, with this new definition of work, Coriolis used calculus and found that if an object was pushed on a flat surface, the object would have a change in one half the mass times speed squared Coriolis therefore decided to make what he called a slight modification to the definition of living force and defined it as one half MV squared, instead of MV squared, to add quote, “simplicity to the principles.” He then found that if you had a machine that pushed an object up a hill then the work minus the wait times the height, equaled the change in living force In other words, the work equals the change in kinetic energy, plus the change in potential energy due to gravity If this sounds like what you learned in high school, you’re right, the only thing missing is heat Now we go back to Carnot hiding out in his brother’s apartment In 1824, Carnot decided to publish his theories about heat engines and heat In this pamphlet, Carnot assumed that he comes from hot objects and goes to cold objects and the bigger temperature difference, the more efficient the engine All things we think true today Carnot also came up with an idealized engine, that’s his most efficient That is currently called the Carnot engine, but then he made a mistake He wrote that, quote, “the production of power is not due to an “actual consumption of heat, “but to its transportation from a warm body to a cold body.” In other words, Carnot thought that an engine absorbed as much heat as it emitted, it was only the movement of heat that caused the engine to do work The idea that heat is a fluid that you cannot destroy or create was called the caloric theory and was very popular in France at the time Over the years, Carnot start to rethink his idea that heat is an indestructible fluid He wrote in his notebook, “heat is simply a movement among the particles of bodies, “wherever there’s a destruction of motive power, “there is at the same time, “production of heat and quantity, “exactly proportional to the quantity of motive “power destroyed, reciprocally, “whenever there is a destruction of heat, “there is a production of motive power.” Tragically, before he could publish these thoughts, Sadi Carnot died of cholera at age 36 And these thoughts were only published in 1890, years after others gained fame for this discovery Very few people read Carnot’s book while he was alive, but two years after his death, another Frenchman, an engineer named Paul Clapeyron based his book on heat engines on Carnot’s book, which slowly gained popularity Whew, that’s a lot of people and ideas Let’s do a little recap, in 1747, Emilie du Chatelet combined the ideas of conserving living force, MV squared with Newton’s ideas And her theories were plagiarized, memorialized in the French encyclopedia of 1751 In 1807, Thomas Young calls the living force energy to make it easier for the ladies In 1824, Carnot published his book on heat and is ignored for 10 years In 1829, Coriolis defined work as force times distance and redefined the living force ie. the kinetic energy as one half MV squared In 1834, Clapeyron published his thoughts on Carnot’s work, including the idea that heat flows from hot to cold and the erroneous idea that heat is indestructible Now we move back to England and a young brewer named James Joule In 1840, 22 year old Joule decided to systematically study if an electric motor would be more efficient than a steam engine in his boggling factory Joule then found the equation for the amount of heat that a resistor will produce as a function of the current through it, an equation we still use today Joule also studied how much chemical energy came from the battery and was surprised to find them equivalent

He then became obsessed with the science of heat and started building elaborate and astonishingly precise devices, where falling weights would drive a spinning paddle, which would then increase the temperature of the water to demonstrate the relationship between work and heat By 1843, Joule was trying to convince anyone and everyone that quote, “wherever mechanical forces expended, “an exact equivalent of heat is always obtained.” But Joule was not a professor He was just a lowly brewer and most people didn’t listen to him He kept on talking though In 1847, he gave a talk at Oxford where he greatly impressed the audience, including a 23 year old Scottish math and physics phenomenon named William Thomson Thomson was impressed with Joule’s experiments, but he didn’t initially agree with his conclusions See Thomson had read Clapeyron’s book about Carnot and was a huge fan of Carnot and Carnot’s theories He therefore thought that in order to like Carnot, you had to believe in the indestructibility of heat Thomson decided that Carnot’s theories were a good theoretical basis for creating an absolute temperature scale and became the first person to correctly get that absolute zero is 273 degrees Celsius below freezing By the way, Thomson was knighted 44 years later, and became known as Lord Kelvin, which is why the absolute temperature scale is measured in Kelvins in his honor Anyway, this paper of 1848, Thomson mirrored what he thought were Carnot’s theory about the caloric saying quote, “the source of power is not in any absorption “and conversion of heat, “but merely in a transmission of heat.” Although Thomson did add in a footnote that quote, “Mr. Joule of Manchester made some very “remarkable discoveries, “which led to a contrary opinion in heat.” This paper made Carnot’s theories instantly and internationally famous In addition, Joule was delighted to have a real scientist mention him even in a footnote and they started a correspondence which led to a fruitful collaboration Eventually, Joule became a famous professor and the units of energy are called Joules in his honor Meanwhile, back in January of 1849, Thomson wrote another paper This one only about Carnot’s theories It was this paper that led to the last scientist on our list, a quiet German named Rudolf Clausius Clausius was born in 1822 and was the youngest of 18 children Yup, I said that right, 18 When Clausius was 21, his family ran out of money, probably all those kids And he had to drop out of school and become a high school teacher and get his PhD while he taught high school He remained a devoted teacher his entire life, and continued to teach even on his deathbed When 26 year old Clausius read Thomson’s papers, he was intrigued It felt like it might be a way to make his name and get out of teaching high school Like Emilie du Chatelet over a hundred years before, Clausius took what seemed like desperate and opposing ideas and elegantly meshed them together In 1850, Clausius came up with a new theory that was quote, “opposed not to the real fundamental “principles of Carnot, but to the addition, “no heat is lost.” Clausius wrote that Carnot’s theories, and the idea that heat is a form of energy, that can’t be destroyed or created quote, “may not only exist together, “but that they mutually support each other.” And Clausius included a new idea that he called interior work But we now call internal energy, which he gave the letter U In fact, one of the modern forms of the first law that the change in eternal energy equals the heat added minus the work done by an object is exactly how Clausius put it with the same sign conventions and the same letters used With this paper, Clausius made his mark on the scientific world and finally got a job as professor Meanwhile, Thomson said that he independently realized that Clausius was right and that heat is not conserved, but energy is Between 1851 and 1855, Thomson published a series of papers on the nature and mathematics of heat and energy transfer In these papers, Thomson used the term energy instead of living force and in 1852, Thompson divided energy into two types, statical and dynamical, which was very good etymology in my humble opinion However, another Scottish scientist named William Rankin named it potential and actual at 1853

and Thompson renamed it potential and kinetic in 1855, the names we’re stuck with today Although Clausius had innumerable petty arguments with Thomson, he agreed that the name energy was appropriate as quote, “an abbreviated mode of expression.” And by 1865, Clausius had formed the first law to be quote, “the energy of the universe is constant.” As Richard Feynman said, quote, “conservation of energy is the most abstract idea “because there’s not a description of a mechanism “or anything concrete “It’s just a strange fact that we can calculate some number, “and when we finish watching nature “go through her tricks and calculate the number again, “it is the same.” But as a mathematical trick, it sure is powerful In 1881, Thomson wrote quote, “the very name energy first used in its present sense “by Dr. Thomas Young is now a principal pervading “all nature and guiding the investigator “in every field of science.” Back to Clausius, Clausius wasn’t done yet, and in 1854, he came up with a new second law, which had to do with the heat divided by the temperature Clausius stated that for a perfect reversible cycle, the heat divided by the temperature for the full cycle would add to zero, and for anything else, this quantity would be positive In 1865, Clausius renamed this function entropy, but what is entropy? What does it mean? Why did he name it that? And what does it mean about our universe? Well, that is next time on the Lightening Tamers Thanks for watching my video Sorry, it turned out so long It just kept on multiplying with more people and more stories If you like this one, you’ll extra like my other ones, because they’re shorter, involve less people Check them out, if you like my videos, why don’t you subscribe? Give a thumbs up, share it on social media, all that jazz If you really liked it, why don’t you consider becoming a patreon? And then you get to see the videos a day early and you get extra special videos And you’ve just learned that you’re a wonderful person Big thank you to my patrons who supported me I really appreciate it Have a nice day, bye Assumption of (stutters) I can’t say that fricking, I can’t say the word