Reversibility & Irreversibility: Crash Course Engineering #8

[@oldcowbb]

"Thermodynamics is a funny subject. The first time you go through it, you don't understand it at all. The second time you go through it, you think you understand it, except for one or two small points. The third time you go through it, you know you don't understand it, but by that time you are so used to it, so it doesn't bother you any more."

[@onetwo4833]

Oh how inspiring hahaha. Thanks..

[@noodlegod1031]

sound like a back subject to me

[@yarely]

SHOUT OUT TO CRASH COURSE FOR HI-QUALITY VIDEOS!

[@nightdreamer2315]

I’m not studying engineering but this was very interesting to me.

[@matthewclements6603]

The first law of thermodynamics is that you do not talk about thermodynamics.

[@ALTDOK667]

Lisa! In this house, we obey the laws of thermodynamics!

[@moonkookie1505]

Great videos, I love that woman's enthusiasm, really easy to listen to and follow, when i typed engineering basics i would've never thought I'd find mini series on it, made my day

[@helenal.vaquera373]

You know it's gonna be a good day when Crash Course uploads a video

[@kelvinkang5109]

Love your videos, but the example with the reversible two bricks + piston is not very clear. Some numbers plugged in would be helpful, so that we can see that breaking it into smaller pieces reduces the overall work :)

[@pranavkulkarni1414]

@@will123134 oh I thought you lift the tiny piece of brick off the Piston and leave it beside it's new height. Then there will be no work done during compression.

[@krispbreadd]

This is a late reply, but for anyone watching these videos really late like me, I thought I’d put an explanation in with the numbers. Previously, she said that Work = Force times Distance, and this is needed to understand the rest of the explanation. Let’s assume that the piston is 1 foot high, that the brick weighs one pound, and that the piston is sitting on a table. After taking the brick off of the piston and putting it on the table, the piston rises to its full height of 1 foot. To put the brick back on the piston, you’d need to exert 1 pound of force over 1 foot, which (according to the equation I said above) means that you’d use 1 unit of work to get the brick back onto the piston ( 1 pound times 1 foot = 1 unit of work ). If you instead break the brick in half, when you take the first half off and put it on the floor, the piston extends to half of a foot. When you take the other half off and leave it at the height of half a foot, it extends to the full foot. To put the weight back on, you would first take the higher half-brick and put it on the piston, exerting 1/2 a pound of force over 1/2 of a foot (since it’s already halfway up). This would exert 1/4 of a unit of work ( 1/2 a pound times 1/2 a foot = 1/4 of a unit of work). You would then take the half-brick that’s on the table and put it on the piston, exerting 1/2 a pound of force over 1/2 a foot (since the piston is halfway down thanks to the other brick). This means you’d exert another 1/4 unit of work (1/2 a pound times 1/2 a foot = 1/4 unit of work). In total, you would have exerted 2/4 units of work, or 1/2 a unit of work compared to the 1 unit of work exerted when you lift the whole brick the whole way up. Hope this helps!

[@rokaszvirblis5946]

@@krispbreadd Amazing clarification!

[@krispbreadd]

Rokas Zvirblis (:

[@LA-MJ]

Terms (un)used in this video: differential, integration. Colour me impressed

[@engibear6392]

*I hope this series has time to get into some concrete examples (both figuratively and literally). So far it's all been very high-level and conceptual, and even then, I'm not sure the law of conservation was really done justice. Input/output balance concepts are super applicable to pretty much everyone's daily life.*

[@mortuos557]

Complete reversibility simply carnot be done...

[@mortuos557]

Dustin James i guess someone didnt get the joke...

[@locabal8354]

Chemical Engineering Intensifies*

[@Doping1234]

Nice one!

[@cooldudeachyut]

Ayyyyyyy

[@JR-rk5dr]

i found this a great warm up before reading my thermodynamics text book :) thanks

[@emreosmanoglu1228]

Reversibility is an important thermodynamic aspect of mechanical engineering. The term 2nd Law Efficiency defines the efficiency of any machine with respect to reversibility. As mentioned in the video, there will always be some irreversibilities (theoretically there could be no 100% efficiency, also in pratice it wasn't achieved). In the video, efficiency is defined very cruedly since there are various types of efficiencies (one mentioned above, thermal efficiency is another major one). It is sad to see that the 2nd Law of Thermodynamics didn't mentioned in the video since it is very important for the reversibility.

[@daemon1849]

I like this show, the host does an amazing job

[@zhubajie6940]

My favorite subject... Thermodynamics, heat and other energy transfers, and fluid dynamics

[@rider18287]

There's a small correction, work done on the system is -ve and work done by the system is +ve

[@SunriseFireberry]

Reverse engineering? Now there's an idea.

[@noticias6111]

What was brought up in this video was not about that?. I do not know.

[@Mayordomo32]

Is that like reverse racism?

[@ioan_jivan]

The brick problem was awseome :D

[@themac9677]

I'm sad that you guys skipped aerospace engineering! I guess you're saving the best for last!

[@lightyears6580]

Favorite question of my chemistry teacher .....difference between irreversible and reversible processes.

[@kurtlindner]

New favorite episode in this CC.

[@gigigggigi]

tbh i feel like teaching a music theory course in this way would be very cool and i bet people would watch.

[@hiteshgupta8474]

I keep a record of days with these videos😂

[@mikey10006]

This has been my favourite video out of the series so far woohoo! The mechanical/electrical engineering ones were good too tho

[@mhtsaklas]

That office space reference, you're the best thought bubble.

[@othmanalghamdi9615]

you made it very insternteing and fun to watch please keep up the good work!

[@m33ks]

I am no engineer and maybe I have no idea what I am talking about but I feel like the example was a bit off. Ultimately I feel like you exchanging one work for another. Now instead of the weight, you have to move the massive volume of infinitely tiny pieces of brick and the Piston is doing the same action with the tiny pieces as it was with the whole brick. You put the brick or tiny piece on the Piston, it goes down, you take it off and it goes up. Am I just missing a key point to the example? Also don't get me wrong, not trying to give her a hard time also. She is doing a far better job at this then I prob would.

[@cybro8925]

I think It's because that whole mass doesn't have to move the same distance. Each part is then able to move only the required amount which requires less work. It's an unrealistic example, but an example still.

[@m33ks]

Just watched it again, I think you are right. Thank you

[@AthAthanasius]

Indeed the small pieces of brick still have to be moved sideways overall (perhaps some up and down motion too, they were phasing through the cylinder wall in the animations!). This requires accelerating and then decelerating them, something that itself will incur losses in any real system. And the whole example was skewed, because why not have the whole brick only lifted up to a platform at the maximum height of the cylinder platform, rather than all the way down to the ground and back up again ? To match this part the half bricks would have needed to be placed on the ground as well.

[@garlicblink871]

THE MINI RUPAUL IN THE DRAG RACE CAR IM SNATCHED

[@rodrigoborges3876]

Come thruuuuuuuuuuu STEM gays!

[@Saffron194]

I like true way she explained and loved her accent as well 😊

[@Kaldorey]

For car engine efficiency, you could also have the example of cars with Internal Combustion Engine having an efficiency of 17-21% out of gasoline, while Electric Vehicles having an efficiency of 59%-62% out of the grid. Yay, go electric vehicles !

[@Poorgeniu5]

Suck, Squeeze, Bang, Blow. Yep, that essentially how piston engines works!

[@abdulbaitsdehanapadmaswast4567]

I love to see the presenter a lot! She's wow

[@madladdan]

Surely breaking the brick in two and lifting it a smaller distance twice is the same as lifting a whole brick the full distance? The weights add up to the total weight. Thus the half forces add up to the total force. The distances lifted also add up to the full distance lifted.

[@pratikshagwalwanshi8676]

I would request you to make videos about turbines, pumps and fluid mechanics and dynamics

[@12388696]

Nice explanation, indeed

[@Lucky10279]

Is infinitesimal calculus useful in figuring out how to make a process as reversible as possible?

[@ronaldochigerwe9610]

loooved this video, so helpful....and if l may ask @CrashCourse, which software did you use for the brick and cylinder animation

[@odyseuszkoskiniotis6266]

Amazing explanation.

[@LelouchVelvet]

So engineering is like alchemy but cooler? Nice.

[@dan1204hc]

This is basics for Thermodynamics in Chemical or Mechanical Engineering.

[@4-thermalstatistical352]

Nice

[@calixdazeroth1422]

that was enlightening

[@kinfemichaelmelaku2280]

It was helpful thankyou

[@minkijeong8156]

Very intersting

[@saphirbvb6862]

As far as I understood, can we consider nuclear reactors as the closest processes to reversibility?

[@xXxFaLLeNxShaDoWxXx]

Crash course thermo?

[@dylanandresjimenezandino7440]

I liked the video

[@gregoryspoto929]

Flashbacks to Thermodynamics oh geez!

[@sniperking2009]

Ma'am work done by the system on surrounding is +ve. As ball expanded it has done work on the surrounding. How come the work is negative then ?

[@garekbushnell4763]

Hello, Ashwin. The convention in the US (and perhaps the British share this convention) is to consider work done to the system as positive and work done by the system as negative. I agree that it is a valid choice to switch them, and have work done by system be positive. One way or another may be picked, and the important thing is to be consistent in your choice.

[@Dasepho]

I don't think the word "engineering" comes from "engine" at all. It originally comes from "ingenuer" or something like that, the same root as"ingenuity", meaning "one who creates new ideas"

[@aotq]

ingenium>engine>engineer(machine/engine operator)>engineering(the discipline)

[@rsiraistlin2473]

Shaft work... Snickers....

[@ghetoknight7801]

SNIKERS I just did this cause yes

[@ghetoknight7801]

Io.here's

[@melonlord1414]

I'm not so sure about the piston as example for irreversiblity.

[@oldcowbb]

me too, isn't a controlled expand example of reversible process?

[@julioramirez8069]

I don't like it either, the best explanation would be throughout entropy increasing but I guess infinite amount of reversible processes is the simplest explanation

[@toniaa-y3559]

I commented because of 'Melon Lord' and the toph display pic tbh

[@trevorzauner6670]

What's with the "Hamilton" bystander at 0:08? Anyone understand that?

[@onetwo4833]

Looks behind myself for backing truck at the end of each video lol..

[@studiorose11]

What if when the piston goes down to a measured level the sand falls out areas in the side.

[@augustuscaeser8939]

can you please make a course on game theory

[@alpuysal8567]

It is kinda a good speech of you but you are investigating the term work as a scientist approach. Engineers assume the work is positive when the system does work. Please consider this detailed but important info

[@VitruvianSasquatch]

If only there was a universally accepted convention for positive/negative work...

[@ameenmuhammed5592]

thank you thank you!!!!!!!!!!!!!!!!!!!111

[@alext9067]

Couldn't find anyone easier to understand than this?

[@qpSubZeroqp]

alex tworkowski she's so clear and concise. How are you having an issue?

[@alext9067]

I don't agree.

[@betht840]

listen to it repeatedly(2 or 3 times or as much as you need) ..you'll eventually get it.

[@polarisukyc1204]

Was that hank green getting a suntan

[@AsphaltYt-4]

Superr

[@mba2ceo]

what happens if U use a LEVELER ?

[@Juan_lauda]

lets ignore the violation in the brick example

[@6alecapristrudel]

Holy mother Entropy needs to be paid what she's owed.

[@FlesHBoX]

I wonder whether a bomb would be considered reversible or irreversible... I suppose it depends on how you look at it.

[@magzieforfunj187]

Engineering is not named after what we call engines today. Siege weapons were called engines before steam engines existed and were built by engineers.

[@salacommander2674]

Which came first, the engine or the engineer?????

[@colsoncustoms8994]

the egg

[@akiohiro7112]

I would say the engineer cam first@@salacommander2674

[@bestcakesdesign]

Why we study reversible process

[@s3cr3tpassword]

i'll be doing some shaft work tonight

[@rparl]

s3cr3tpassword You wish.

[@mongyunkim749]

Is it physics ?

[@kraftytactician5529]

I guess life is some trade-off that you can't escape from. The more output you want in favor requires more work, and more work is out of your favor so you slack off..

[@cybro8925]

W = Fd has a lowercase 'd'

[@mohamedmagdy-xu2yu]

yes that is a truth how ever i am not satisfied about the currant day machines turbine engines etta = 45% petrol engines = 35% diesel engines = varies between 35 to 45% old school engines max 25% even electrical motors = 85% you might want to cover perpetual motion machines

[@bosslevel9992]

ya'll are fast

[@mach2570]

Work is the force multiplied by the displacement ,not the distance.

[@onlycontact6070]

Cryptobiosis should be a major CRISPR gene editing idea. Eye wonder what would happen if OM have them live inside us. The Tardigrade could help us last Elon Musk’s next plan with what he’s been posting lately.🖖🏿🐘🔊

[@dustinjames1268]

Tardigrades are actually terrible at survival. They're resistant to everything... except what would actually kill them They can survive in space... except they can't There is no good argument for them being good at their only job - to live

[@abhaysharma9317]

Doesn't it seems to like the resting period of a piston has arrived when pistons will sit on a back of a garage and see the fast pacing sexy electric motor rotating at that high RPM that the piston have never thought of. Miserable Piston.

[@abhaysharma9317]

I meant we are done with the combustion engine car, No combustion engine car no use of piston and electric cars have just motors to create torque.

[@peter4210]

Why not use a electrical engine, They are reversible, and could have been used for a example instead of the brick on a piston

[@jakobkrey9789]

King Peter they arent 100% reversible

[@peter4210]

Jakobmaximus like anything, but it's a better example then a combustion engine that cant be reversed at all. A other alternative could be a sterling engine wich when run in revers with a other engine it turns into a heat pump instead of using departure difference to turn a wheel

[@Dluv021]

Half-a-brick whole brick aha

[@TheVexinator]

Why is the CrashCourse audio team putting beeping noises into so many videos lately? Please stop.

[@niv6924]

MKBHD’s secret sister

[@andyroidify]

Shaft work lol

[@trappakappa8950]

Yo wassup

[@w.e.4277]

Or as Elon Musk would put it: reusability

[@bandibabyrani862]

Please say slowly

[@empi1972gtv]

Are you single? Asking for a friend.

[@JerryRMartin]

Sand, friction, and metal doesn't mix. I understand the explanation, but the material used just isn't compatible for real life production.

[@LuisSierra42]

no way!!

[@matthewcapobianco9332]

Its the only way to teach calculus to lay people.

[@matthewclements6603]

Thanks for clearing up that the thing she said isn’t possible, is in fact, not possible.

[@cookycamy101]

She's explaining a concept, bro, not a real life application.

[@JerryRMartin]

Yeah. I understand. I just prefer filing content in my brain as it's applied in real life. Thanks for being respectful in your response. :)

[@jesterkids2246]

8 veiws??

[@Scorpionwacom]

Dislike for washed out colours in the video.

[@starvingboyinafrica9463]

I thought this was going to be about sunburns from the thumbnail >:(

[@Tuckems]

Starving Boy In Africa If you can have a Mobile Phone/Computer to comment on here how do you not have food? How are you on yt? Just use the wifi to order a pizza on papa johns or something

[@annoloki]

Engineering is filthy

[@LuisSierra42]

and that's why it's awesome

[@uzairmehran8542]

Omg lots of sss ss sss ss ssss

[@rparl]

How about useless work, where a politician lies to assure his future power? Edit: Sorry. I'm upset about what's happening these days.

[@salacommander2674]

Hate to break it to yah, but it's been like that since the beginning of society. It's not just a 'now' problem, it's a humanity problem.

[@ChainsawDunDeez]

Speaking about heat...the presenter is hot... But I'm a sucker for tan skinned brunettes... The cute accent is just a bonus...

[@dylanrodrigues]

Are you... ok?

[@ChainsawDunDeez]

Ford Prefect ..different tastes for different dudes...

[@busteronlyfullscreenmode]

I'm just glad you don't sound like an actual serial killer.

[@Tinman_GG]

Click bait hottie engineer. Such bore , such cute, very accent