Why We Can't Invent a Perfect Engine: Crash Course Engineering #10

We’ve introduced the 0th and 1st laws of thermodynamics, so now it’s time to move on to the second law and how we came to understand it. We’ll explain the differences between the first and second law, and we’ll talk about the Carnot cycle and why we can never design a perfectly efficient engine.
This episode is sponsored by CuriosityStream: curiositystream...
Crash Course Engineering is produced in association with PBS Digital Studios: • All PBS Digital Studio...
***
RESOURCES:
www.thedrive.co...
newsroom.toyot...
www.gepower.co...
www.gasturbinew...
www.livescienc...
www.khanacadem...
www.zo.utexas.e...
theory.uwinnipe...
www.britannica...
www.britannica...
energyeducation...
www.britannica...
Çengel, Yunus A., and Michael A. Boles. Thermodynamics: An Engineering Approach. 8th ed., McGraw-Hill Education.
***
Crash Course is on Patreon! You can support us directly by signing up at / crashcourse
Thanks to the following Patrons for their generous monthly contributions that help keep Crash Course free for everyone forever:
Mark Brouwer, Erika & Alexa Saur Glenn Elliott, Justin Zingsheim, Jessica Wode, Eric Prestemon, Kathrin Benoit, Tom Trval, Nathan Taylor, Divonne Holmes à Court, Brian Thomas Gossett, Khaled El Shalakany, Indika Siriwardena, SR Foxley, Sam Ferguson, Yasenia Cruz, Eric Koslow, Caleb Weeks, Tim Curwick, D.A. Noe, Shawn Arnold, Ruth Perez, Malcolm Callis, Ken Penttinen, Advait Shinde, William McGraw, Andrei Krishkevich, Rachel Bright, Mayumi Maeda, Kathy & Tim Philip, Jirat, Eric Kitchen, Ian Dundore, Chris Peters
--
Want to find Crash Course elsewhere on the internet?
Facebook - / youtubecrashcourse
Twitter - / thecrashcourse
Tumblr - / thecrashcourse
Support Crash Course on Patreon: / crashcourse
CC Kids: / crashcoursekids

[@syedtamsilhussain]

I am a mechanical engineering graduate and this is the first time I understood Carnot cycle clearly

[@waleedghayas9031]

I love how you defined entropy as not simply randomness, but how energy ends up being converted to useless forms.

[@cyrilyago8214]

Did they just portray nickleback as unusable form of energy 😂 at 2:10

[@evanjones8049]

Crash Course is legitimately better than the thermodynamics course that I am taking at my university.

[@SaeedAcronia]

I am an aerospace engineer and I have been mocked by these "physicists" for being an end-user of their theories and equations. Guess what?! Sadi Carnot, the father of Thermodynamics, was actually a mechanical engineer. On behalf of all mechanical and aerospace engineers in the world: IN YOUR FACE Sheldon Cooper!

[@Lucky10279]

The way I see it, the 2nd law isn't _fundamentally_ about energy at all. Rather, it's all about probability. It's not that we _can't_ make a perfectly efficient engine, it's just the the probability of it happening is practically 0, but actually slightly higher. What's really going on is that entropy is a measure of the number of states a system can exist in. We talk about macrostates vs microstates. For example, if our system consists of a single vase, one potential macrostate would be "broken". A microstates is an exact configuration of particles. There are FAR, FAR more microstates that correspond to "broken vase" than "not broken vase", so a system consisting of a broken vase has higher entropy than one consistenting of a whole vase. This is where the misleading description of entropy as being a measure of "disorder" comes from. Most macrostates we'd consider disordered are higher entropy simple because there are more microstates that correspond to them. But this isn't what entropy is about. So what does this have to do with energy and efficiency? Well anytime we apply energy to a system to do work on it, we're changing the state of the system. Even if we intentionally apply the energy in a very specific manner, there are simply SO MANY ways for some of the energy to be wasted compared to the number of ways for it to all be used for useful work. There's nothing _stopping_ a 100% efficient heat engine from existing, per se, but the probability of it even a single perfectly efficient heat engine cycle to occur is such that we'd never expect it to happen in any way imaginable amount of time. _However,_ given infinite time, it's virtually _guarenteed_ to happen, not just once, but an infinite number of time. That's because _anything_ with a non-zero probability of occuring, no matter how tiny, will eventually occur given a sufficiently long period of time. However, the probability is such a thing is probably on par with the probability of all the particles in your body quantum tunneling at the exactly the same time in such a manner to teleport you someplace. It theoretically _could_ happen, but don't count on it. I think the amount time needed for it to have even a 50% chance of occuring is longer than the age of the universe, though I'm going on memory.

[@skydivekrazy76]

We should find Carnot's burial site...

[@RobertNeyrinck]

Can we talk about how she said “unusable energy” and the graphic was a nickel back album

[@bidaubadeadieu]

I'm in my final year as a physics undergrad, but due to chance and schedule conflicts, I won't get to take Thermal Physics and thermodynamics until next spring, my very last semester. I'm really loving these episodes, they feel so fresh and exciting compared to the topics I'm more familiar with.

[@apeman2035]

You need a good edjukayshun, yep!

[@robertbilling6266]

Thanks for that, filled me with nostalgia for Dr Cohen's lectures in Cambridge 40 years ago.

[@Marylandbrony]

The 2nd Law of Thermodynamics is that you don't talk about Thermodynamics.

[@PatrickAllenNL]

Marylandbrony I laugh

[@minimanofiron2501]

+Marylandbrony mate... thats actually the 42nd law of thermodynamics, thank you very much.

[@OgWoot]

MINIMAN of iron 42

[@ayushwithasingle_a]

what is the reference?

[@ClaraWang32356]

@Sal Vastola It comes from The Hitchhikers Guide to the Galaxy.... (the number 42)

[@Pooskipie]

Shes a great teacher Keep em coming Wonderful show guys love these videos

[@je-fq7ve]

Thanks, in my home we always obey the the four laws of thermodynamics.

[@lewisdavison2275]

thank you for putting it in such an easy to understand and clear video, very well-spoken. Scary how bad my thermodynamics teacher is.

[@mvmcali6900]

Entropy is such a cool concept....it took a genius to define it

[@chance_ooo5663]

engine goes vroom vroom

[@LuisSierra42]

clever

[@sp00machine]

haha yes

[@lego007guym8]

Beeb beeb

[@91722854]

mindblown, I couldn't even come up with that vroom vroom, guess I need to quit being an engineering student

[@chance_ooo5663]

Justin Tesla Chan trust me, it took many years of hard, tedious research to come to this conclusion. continue with your studies brother!

[@Tsagan]

Dr Shini Samara is the best ! Loving the series thus far, continue the great work

[@chickenturtle5026]

Have you ever tried mixing seltzer water with juice? It's surprisingly good.

[@juliansolomone7442]

@mwalsher Thanks! I've been trying to get my treadmill-powered engine charged for days without luck. I've tried this. It works!

[@sylys]

Thanks, finally a clear exposé of what entropy is !

[@thatRyzzle]

Crash Course doesn't like Nickelback, therefore I like Crash Course. It's simple, really.

[@selahattinkaracay9951]

Perfect explanation. Carnot is a real genius.

[@jacker372]

Two dissimilar metal wires twisted togeather into a thermocouple can produce useable power from heat.

[@ceasetheday87]

finally, a definition of entropy that is useful. simply saying “disorder” or “randomness” gives no insight into why entropy would matter.

[@dan1204hc]

You can work and research Thermodynamics following the career of Chemical or Mechanical Engineering. This is an extremely broad field that governs the laws of nature. Therefore the approaches can be extremely different. In CE, it is much more focused on Equilibrium of solutions/mixtures of solids, liquids and gases and different chemicals (which is hardly seen by MEs). In ME it is much more on Heat Cycles.

[@Dayglodaydreams]

There should be another rectangle at the end of the episode that says "Want to know what an Existential Crisis is click here" and the CC Philosophy episode is hyperlinked.

[@dhanapal.sdhanapal.s5657]

Physics is my favorite subject

[@Hypatia4242]

I like this show, but that shelf is messing with my OCD.

[@Kaiju3301]

Hypatia4242 ikea strikes again

[@zhubajie6940]

So glad you are helping spreading the word on the issues that confront and limit the energy engineer to solve the problems that effect our world so much such as climate change and energy depletion. We're not magicians just artist using the pallete of engineering physics.

[@TalentedOnion]

Mr. nobody was a great movie. Underrated.

[@mukamuka0]

Very informative and great animation. I'm impressed.

[@abdelrahman4436]

does the second law of thermodynamics actually restrict the inter-conversion between heat and work or does it restrict the efficiency of the inter-conversion between heat and work

[@sebastjansslavitis3898]

in russia incandescent light bulbs have 100% efficiency

[@MrJuuustin28532]

I think your videos are great. The fact that only 10% of veiwers at this moment give it a thumbs up says people and subscribers need to wake up. Thanks for the wake up call even if we the viewers only give it a like in one out of ten views. Personally I plan to rewatch them and share them with my children. Awesome! thankyou!

[@noahmillican1394]

Could you do one on fuel cell engines and how we might be able to convert the hydrogen more efficiently for a full working type

[@stevieinselby]

The world would be a better place if entropy was measured in degrees Clausius

[@AvenEngineer]

We already have, they're called electric motors. 95+% efficient is pretty good. Maybe CrashCourse could do a video on the VW I.D. R.

[@rafetizer]

So if we made one that was 100% efficient it wouldn't be MORE perfect? The point here was based on 100% thermal efficiency, even if the title doesn't exactly specify.

[@yolo3004]

5:48 why does it feels like im watching a movie? also i had to watch it 5 million times to understand it.

[@madscientist8627]

This is really cool! I always loved learning new things, thank you!

[@hafshahalim5747]

Couldn’t see anyone talking about how amazing her background shelf

[@PoorManMods]

The nickel back album was hilarious haha

[@Vikingheland]

goddamn entropy with your cut of the energy. I bet you're saving it for a big bang

[@raikiri6251]

Happy to hear Your voice again Shini! It's been a while since I finished my 12th grade & stopped watching CrashCourse

[@alexanderbilchuk8915]

Some Fullmetal Alcimist lessons done right here. Good job guys!

[@AyanAli-eq4lo]

Mercedes petronas’s 4 cylinder turbo charged engine is close to 60% thermal efficiency

[@TheMahmoudTalaat]

Thank you this video helped me a lot and explained things that i didn't understand before and i watched it more than once in different time to remember or understand things Thanks a lot

[@andreadorado884]

I love your videos, they always help me to understand and solve my homework :D

[@vaibhavsingh6760]

This is the best series by the way than G0T as well

[@chrisjamel8461]

To decrease entropy is to travel back in time

[@mkb6418]

You should saw a P-V diagram. It would really explain why and how Carnot desinged his engine. Now it's just like "it's this trust me"

[@tahoon2009]

awesome, best explainatoin and visualisatoin for carnot found so far, best to the whole team :)

[@damiensadventure]

Who is this lady? She is awesome and knows her stuff.

[@Bird_Dog00]

Dr. Shini Somara. Physicist and engineer. Her specialty is afaik fluid dynamics. She's ben doing this kind of outreach work for some time now.

[@abdilkadermohammed4656]

you made engineering so easy thank you espeacially thermodynamics

[@themightychondria]

what about the 2J?

[@sweetgoldilocs2]

I'm too dumb for this. I do however give myself credit for making it half way through.

[@apeman2035]

Try again I believe in you

[@dirtymikentheboys5817]

Dr. Shini Somara Or Crash Course, can you do one about how the Arc Reactor (Tony Stark) achieves over 110% efficient and how it COULD be possible, Like for a Halloween special? Thanks even if you don't and I like history and engineering videos.

[@angelojustinezaraspe9214]

Does the thibgs on the shelf are glued?

[@macbuff81]

entropy. Brian Cox has some very good segments about it too

[@Aramis419]

Nickleback XD!!

[@jbrone21]

subtle, yet beautifully done .

[@UteChewb]

"less useful or unusable", pic of Nickelback comes up. Harsh but fair. :D

[@Hypatia4242]

Scrolled through the comments just to see if anyone else had noticed. Love this channel.

[@matthewfredrickmfkrz1934]

While thermal efficiency is only 25% from the 4 stroke action modern engines are volumetrically 95% or better with forced induction... cooling with the fuel is used in jet turbine engines to also prep the fuel for combustion... Smokey yunick made a "hot air engine" and got 500 HP out of a 2.5l modified ironduke fiero based on experience of an engine running amazing just before blowing up and hydrogen Reformation

[@TheAzachiel]

And what about all those patents for permanent magnet motors or SERL effect generator?

[@andrewkelley7062]

You have to use state changes in exotic circumstances. There are two ways either create a harmonic vortaic system that uses outside thermal noise to power the system or create a system that throws itself into a constant state of unbalance by it operation to the point where you get a separation of thermal states then pull the work off the collapseing phase change which can be introduced to the system.

[@oldcowbb]

i hate calling entropy disorder, it's very Bayesian. Also, saying that the entropy of the universe always increase is assuming the universe is a isolated system, which we don't really know.

[@SiraSam]

I have no friend in Engineering college T T feels so bad man.

[@oldcowbb]

you don't need

[@yuven437]

How does the conservation of energy work with red-shifting photons?

[@MGJ182]

Kyubey pls.

[@ryanbegley7098]

Fantastic episode, thank you!

[@joserenato5882]

Loved it. Thank you very much.

[@Dayglodaydreams]

Good episode team CC Engineering.

[@suriyajabeen7744]

Video not uploaded on this thursday. I'm missing it

[@Hakeem94]

Idk who this is, but she’s smart and cute AF!

[@proknight6647]

Can anyone please tell me why we cannot create an exact recreation of the Carnos Cycle? CC Team pls?

[@bomguy999999]

We did invent the perfect engine. The 427 was about as good as it gets.

[@devilsoffspring5519]

Depends on what you mean by perfect... 427 V8? Excessively big & heavy, low power output per cubic inch when emissions-legal, very poor fuel economy in normal everyday use. Hardly "perfect".

[@dnimlarebil]

2:17 sideburn Nickelback!

[@shenanigansonyoutube2901]

0:27 Yeah you can, its called a VQ35DE, or a 13B-REW

[@kieranmales5889]

Thanks you too much your such a great teacher and your voice is very easy to listen too! Way better then Khan academy lol

[@MrJkaos96]

I really understud what the second law of thermodynamics means, Thanks!

[@apeman2035]

You're welcome, Peaches !

[@lotuskamal459]

I would like to play this vedio at 0.5x playback speed...... now it's perfect......🙂🙂

[@titankorellc2937]

I'm designing a new kind of stirling engine that can use solar heat and theoretically has 45-55% heat efficiency and can be 90% 3D printed.

[@apeman2035]

Theoritically, huh ?

[@VarretInxve]

I don’t understand why we need 4 parts of the Carnot cycle. If we were just doing isobaric heating and cooling(changing temperature while keeping pressure constant), we’d get the piston to move because of changing volume. And if we assume no heat being lost to the environment(like perfect reservoirs in Carnot cycle), we’d get 100% efficiency.

[@VarretInxve]

Okay, I think I got it. Those isobaric processes would be 100% reversible if we assume that no energy is lost, but actually no energy is transferred to the environment either. If we had a vertical piston working as an elevator, and we heated up the gas inside the cylinder, the piston would go up, but the moment you remove mass from the top of it, pressure in the cylinder would go down, so the piston would go up and if you wanted to bring it down to the initial pressure and level, you would have to put some mass on top of it, but since that mass would go down with the piston, its potential energy would decrease, so no work is being done.

[@danconrad920]

Varret, I think your talking about a sterling engine.

[@harveyspecter3361]

You need a doner kebab broodje!

[@humblesoldier5474]

Isn't a Hurricane an irl perfect engine. I know it is to big to use right now, but the universe does allow for perfect engines that violate no laws with the right scale and material. For human scale finding a way to stabilize liquid He, and other meta materials might get us the closest we can get at human scales.

[@NoahNobody]

Dig up his note books!

[@giantred]

Thank you for teaching me stuff :)

[@subhasarkar7465]

Thank you ...

[@ArchesBro]

Rankine cycle is the next video I guess

[@coby_e]

they got a baddy doing these now im boutta be hella smart

[@AdamCHowell]

Looks like a lot of entropy was gained putting up those shelves.

[@EmonKhan-sw1fx]

Well how efficient is the human engine?

[@hampsterdanny]

I keep thinking about Muse's Isolated System whenever she says entropy

[@ballHand]

Stirling engines are cool

[@XenogeneGray]

Entropy is a surprisingly complicated and misunderstood concept.

[@oldcowbb]

not surprisingly

[@tucker9162]

Maybe just me, but whoever edited this video with no gaps between paragraphs is a genius. Makes the narrative compelling.

[@GarretSlender]

My rotary goes BRAP BRAP BRAP

[@jewelhosiery5664]

Nice explanation 😊👌👍😘

[@samyaksheersh712]

PLEASE UPLOAD A NEW VIDEO. WHY ISN'T IT BEING UPLOADED?

[@ipv2000]

thank you very much for this video :)

[@TheTrueHolyDarkness]

::hypnotically stares at the brown lady-nerd with the British accent and forgets the topic:: Huh? Wut? Oh, right. In other words we're dying. Yep. ... There are still joys in life though. :)

[@docsaq]

God honest description.. 👍

[@nanak3363]

Why " energy per unit temperature that's unavailable for doing work " exists ? Why it happens ? Why not all the energy per unit temperature is available for doing work ? why the concept of entropy has to exist ?

[@KhalidHamad-su8zz]

Great work

[@RespiratoryDrive-vy9ih]

The perfect engine may not be possible but you are the perfect Indian beauty.

[@gray1530]

I put this on at night to help me fall asleep