PV-diagrams and expansion work | Thermodynamics | Physics | Khan Academy
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Why work from expansion is the area under the curve of a PV-diagram. Why heat is not a state function and internal energy is a state function. Created by Sal Khan.
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Weird that Sal does not mention that by swapping the bounds of an integral you get the negative value for the integral. Very valid here on the PV diagrams going "forward" and "backward" as work is done by and done on the system.
Hy there I'm the only who's watching in 2023☠️
No I'm here
thank you for taking the time to explain out all the little things. its been really super helpful, if i needed to learn a whole topic from scratch or just fill in the bits that i missed in class. you rock
Guys, look up giovannibattini
He compiled all these helpful Thermodynamics episodes into a playlist so they play flawlessly one after another
Also, thank you so much for making these videos, uploader!! I really really struggle with Thermo, and have felt hopeless for years with the subject. This is because I lack the intuition to use the basic fundamental formulas because I don't fully understand their origin.
Here's hoping these videos finally help me get there!
Can someone please explain to me the concept of expanding gases cool and compressed gases warm. Wouldn't it be the other way around since KE is proportional to Temperature and if you are increasing Temp then the gas is absorbing heat therefore expanding?
Hey i think I'm ten years late but maybe you'd want to know. So what happens is that, upon expansion, the gas molecules move further apart, and as volume is inversely related to temperature, temperature decreases. When we heat a gas, the molecules' kinetic energy increases yes, but they kinda try to lower their temperature down to gain stability (a higher temperature would mean higher energy and less stability), and they do so by taking up more space
at the start I think delta Q should be Delta U.
I understand that U is a state function, but for the last ex., if ur loosing energy by doing work don't u need energy done to the system to compensate so that change in U is 0? But with the last example there was still a net work the system did.
@azndude3600 Yeah, I also have this question:
If the system does net work, doesn't that come from the internal energy? So how do you net no loss of internal energy, but you net work done?
Heat?
Wow, seriously...good for you Neo! I agree, youtube videos like this are absolutely gold as supplements to text and class-notes. More people need to take advantage
Drink everyime he say Quasistatic process
What is workdone by an aneroid barometer in joules per cubic volume ???
What kind of person would be studying thermodynamics yet has never seen an integral ?
Regardless, thanks for these videos! Great help
How does it do work if the change in internal energy is 0????
Because at the same time it does work it also received heat energy from surrounding or by external means
you are more help to me than my physics teacher
I've loved these videos, great at answering any q i ask at the time it's asked.
1 thing at the end though
Not sure what exactly the area inside the loop represents. when you say it's "the net work it did", how else could the question be phrased?
Thanks
the questions most probably would be of type like as under some specified conditions what is the net work done on the system or net work did on system. maybe the may take away volume or pressure of final or initial state and give work and ask us to find it, but that would require good knowledge of differential equations, if you have taken calculus class
I'm lost at the "Area under the curve". It can't be the area from the bottom of the graph to state 1 and 2... we haven't even defined what the bottom of the graph is (is it implied P=0 V=0? Which doesn't make sense as you can't have V=0 P=>0) ). At state 2 there is energy left in the system in the form of volume at a given pressure. So by showing the area extending from the bottom of the graph he is including the final energy remaining at state 2. Or am I missing something obvious? Should the shaded area not end level vertiacally with state 2?
what is usually implied in "area under the curve" lingo is that it is the area under the graph *to the* horizontal axis. In this case, it would be to the V axis. Why does this make sense? Because when in the video it was said that the area of the (any) rectangle is P times change-in-volume, , the "P" stood for the pressure the graph indicates at that particular V-axis coordinate, i.e., where that particular quasi-state was.. And that "P" is the amount that is measured from the V-axis. Think of how on a regular x-y graph, such as y = 3x-7, a point is (x, y) and the vertical distances are the y-coordinate as measured from the x-axis. Hope that helps!
Dear Sal - In this and related videos you mention adding or subtracting pebbles and show that the system changes (macro) state as a result, all of which makes good sense to me. Where are you accounting for the energy that some entity outside of “the system” is providing to effect these additions/subtractions of pebbles? - Thank you! - Jim
He basically explains the whole concept of the integral, a bit to detailed I would say. Most people watching this have had a course in calculus already..
hello sal....erm,i'm wondering if u know abt the compressed liquid,superheated vapor and some other more which i dont understand... well...can u do some videos abt it? i'm totally blur (v_v)... *regard from ASIA :)
I solved here a doubt of 2 years.
this is so simple... wtf was my prof saying about pv=nrt with right side is 0 for this graphy to exist/ some other bs...
watching this the night before physics ap test.... fuck me
i wish this didnt deviate from u=q+w just makes it a bigger headache
Is T constant?? is T1=T2 ?? so How is adiabatic process diagrammed??
Just an idea - would it be possible for you guys at the khan academy to put links (in the video window) to the previous and next videos of the sequence? It would just help so that when Sal says "in the last video, I talked about ....." , I can then quickly go to it without having to go and search for it.
very helpful explanation, thanks so much
That area has to be zero right?
i havent got the last graph.help me
I like to think of deltaU being similar to displacement, where going back to the starting point yields zero.
Then would distance be the non-state version of displacement?
Hey Sal, I think you should write work = P * A * delta (x). That way it's no so confusing as to why A * delta(x) = delta(V).
Great video :)
watching this video on 2X reminds me of eminem
This video make me clearly understand about PV diagram
Many thanks
Good job man
@MarvelsofaLifetime not a public school. University... yes.
Great explanation; thank you sir!
For some reason the video stops at 5:40.
Could you do a video on clausius inequalities?
13:10 is when the light came on for me. Thank you!
did you just say y'all? that's awesome.
May I know what comes after this video? :)
love this
thank you.
y cant u have delta pressure?
like always man thanks a lot
awesome...thanks a million
Wow i am really impressed
who needs books?
u r a hero!
i love you
you should give examples with calculations, so people like me who need help can learn how to find actual answers, otherwise this vid is kinda not helpfull.
open their website
Dude go straight to the point,, justt tell us the formula, what units should be used, how to solve, my mind got crazy after all
that's now how u learn physics lol