Simplifying the First Law of Thermodynamics | Physics by Parth G

The First Law of Thermodynamics is often said to be a version of the Law of Conservation of Energy... but how is this true?
In this video, we'll be taking a look at how the First Law of Thermodynamics deals with the Internal Energy of a system, as well as understanding the mathematical equation that represents this Law.
Firstly, internal energy is a measure of the state that any system can be found it. Specifically, it is the amount of energy needed to bring the system into the state it's currently in, from an assortment of particles and the like. More info on internal energy can be found here: en.wikipedia.o...
The First Law deals with the CHANGE in the internal energy of a system. It tells us that the internal energy will change if there is some form of heating going on, or some form of work being done. Usually the chosen convention is that if the system is heated, then the Q term is positive (and if the system heats the surroundings, then Q is negative). Heat is simply a transfer of energy (to or from the system) WITHOUT any large scale or "macroscopic" forces involved. Work, however, is usually defined the other way. If the system does work on the surroundings, then the W term is positive in the equation. It is negative if the surroundings do work on the system. Work is simply a transfer of energy WITH the involvement of some macroscopic forces (e.g. the gas pushing on a piston). Thus, the full equation becomes Delta U (change in internal energy) = Q (heat transferred to system) - W (work done by system on surroundings).
Sometimes, it is easier to choose the opposite sign convention for work, i.e. W is positive if work is done ON the system, rather than BY the system. In this scenario, the First Law Equation is written Delta U = Q + W. It doesn't really matter which sign convention we choose to use, as long as we are consistent in all our mathematics once the convention has been chosen.
Another important point worth making is that this formulation of the First Law of Thermodynamics only holds if we assume that no matter can be transferred to or from the system (i.e. no particles can enter or leave it). If this were possible, then energy could be transferred this way, and we would need an extra term in the equation to make sure Conservation of Energy was upheld.
Due to the nature of perpetual motion machines (machines that can basically keep moving / extracting energy from nothing forever), it is often said that the First Law is the Law they would have to break in order to exist - they would have to break the idea of conservation of energy.
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Timestamps:
0:00 - The First Law of Thermodynamics
0:27 - The Law of Conservation of Energy (Energy Cannot Be Created or Destroyed)
0:51 - The Terms in the First Law Equation (and our Gas in a Box System)
1:09 - Internal Energy, U, Contained in the System
2:16 - Heat: Energy Transfer without Macroscopic Forces
3:19 - Work: Energy Transfer with Macroscopic Forces
4:17 - The Overall First Law Equation
4:49 - Clarification About Energy Loss and Gain
5:27 - Sign Conventions and Definition of Q and W
6:18 - Transfer of Matter is NOT Allowed!

[@mufcqw]

the goat of youtube physics

[@nafisarman8266]

Awesome dude

[@suprith-science1441]

Dude apply this video for Veritasium's science contest. This is the best video I've seen on this topic. Compress this video and make a youtube short of 1 min

[@Metalhammer1993]

honestly I prefer the + version. it just makes sense to define work and heat the same if we use them in the same context. plus I'm a chemist. i just by nature want energy going in to be positive and energy going out to be negative. it#s just how all of chemistry works.

[@Ottmar555]

IUPAC convention ftw. I liked that in Philippe Ansermet and Sylvain Brechlet's book "Principles of Thermodynamics" they include a third term, C, which accounts for chemical work. The mudN term in open systems.

[@foxtrot8325]

I prefer ΔQ = ΔU + W. It is more intuitive to me that when heat(ΔQ) is introduced to the system, some of it raises/changes the internal energy(ΔU) and some of it is used to do work(W) on surroundings. In chemistry I just remember to change the sign of Work(W), so it transforms to ΔU = ΔQ + W. The chemistry version does make sense, but when I used to forget the equation, the physics version of the law helped me to derive it again.

[@emersonsouza9960]

I really don't know how thank you for explain internal energy. I'm a brazilian bachelor in physics and in my whole graduation we only use this term but nerver was explain for us. Thank you, really thank you.

[@davidsweeney111]

If you were my teacher I wouldn’t have dropped physics!

[@DrDeuteron]

everyone says that until Parth assigns homework and gives exams.

[@ParthGChannel]

That's very kind, thank you!

[@ParthGChannel]

Haha I would set very doable exams I hope

[@zona8224]

U explain things very well. Good job.

[@MichaelHarrisIreland]

Very good, thanks. The energy goes down when it works on something, the energy goes up when you work on it.

[@eduardotijerina958]

Waiting for the second law 👌🏻

[@keshavgupta3698]

This video cleared my doubt about difference in heat and temperature ❤️

[@foxboro1204]

this has to be one of the best video explanations I've encountered. It is better than reading the textbook (at least for me). Subscribed!

[@pixelphysics3550]

That's hot! Great explanation Parth!

[@md.ayaanahmed5152]

You're a hero for us highschoolers. I mean we always wanted to have the same feeling for the formulas, which their inventors had. You make this easy for us.

[@robertschlesinger1342]

Very interesting, informative and worthwhile video.

[@theartofmusic05]

Good explanation.. I would be grateful. If you could make and another video in 3rd Law of Thermodynamics.. Beacuse 3rd law is so difficult for me to understand it...

[@sakariasakaria6364]

u just made me understand the first law of thermodynamics hope I'm gonna put this law into use as a metallurgical engineer

[@PrashantKumar-kb7pe]

Bhaiya you are great. I love your videos. Especially the wave equation. Thank you

[@vrutpalpatel8851]

Very well explained. Very helpful.

[@mukundanm2666]

Another way of defining this is that the heat supplied to the system is equal to the change in internal energy and the work done by the system..... This makes much more sense tbh😉

[@ahusky4498]

That's why I like the + version more

[@mukundanm2666]

Ya me too

[@nafisarman8266]

Make a video on oscillation

[@hajerkindi6441]

So in simple terms signs of the equation changes based on the perspective we take. Negative by taking the perspective of the surroundings and positive by taking the perspective of the system

[@jiyadubey2750]

You're great sir

[@yuvalkoren4070]

Your explanation videos are tremendous, thank you so much!

[@elirandavidian6142]

Please make a video on the second law

[@Dismythed]

Heat is still technically work, but is caused by pressure differentials in the materials when larger work forces are applied, resulting in vibrations, leading to loss of energy through a release of photons, which are carrying the vibrational work energy away.

[@Threshold370]

Could you explain the difference between enthalpy and internal energy?

[@suheladesilva2933]

Great video, thanks very much.

[@manjitkumar-ee5fr]

Make a video on 2nd law also

[@lewisleslie2821]

Very clear and concise! Brilliant video mate

[@thoughtsdomain5901]

Which app do u use to make videos?? please share with us.

[@santanubanerjee2993]

Are your merchandise shirts available in India ?? I wanna buy them ASAP !! PLSS HELP

[@innocentarain7900]

Please make video on quantum holonmy theory

[@wolfy9005]

Commenting for the algo + made a lot of sense in a short amount of time which might be useful next year when we get onto thermo

[@alwaysdisputin9930]

Very clear TY

[@asgovindarajan5597]

Parth Sir! Studying Electrodynamics and learning about EMF, Voltage, POTENTIAL, etc really messed up with my understanding of the concept of ENERGY. Could you please make a video explaining WHAT EXACTLY IS ENERGY? Please 😭 Edit: Also, my confusion regarding energy is increased by some people saying "Change in state of motion for an object is expensive, but energy bears that cost" - what does this even mean? How does energy influence a change in the state of motion of an object? Please explain such concepts, along with the types of energies in detail sir! 😭 Thanks in advance! 🔥

[@ParthGChannel]

Thanks for the suggestion, I'll definitely add it to my list! A basic explanation is that energy is a mathematical quantity that seems to describe very well how different things happen in the universe. It seems like everything behaves in a such a way, that this mathematical quantity must overall stay the same, but can be transferred from one place to another. So it's just an idea we assign to things we see happening around us, that works consistently with how the universe behaves. Hope that helps a bit.

[@asgovindarajan5597]

@@ParthGChannel Yes it did help clear some conceptual clutter! Thank you sir!! Eagerly waiting for the video😃 Edit: "That mathematical quantity physically manifests itself when 2 charges attract each other and align themselves into a system, and somehow that's called electrostatic potential energy and that mathematical quantity is somehow the reason for electrons to flow in a circuit." - sir, this is where all of my confusion began. 😭 In that video, could you also please explain how electrons flow in a circuit due to some form of ENERGY DIFFERENCE? Thank you sir!😃

[@md.ayaanahmed5152]

@@ParthGChannel I'm a high schooler n I'm very skeptical of potential energy. Does it even exist? I mean they say : When you lift a box up to a certain height, the work that you did to lift up the box is stored and is called potential energy. I say such thing does not exist. The MGH that it would have is just because of its position above ground not because of the work you did to lift it up. Can u plz clear this up ?

[@anonymousperson9052]

@@md.ayaanahmed5152 exactly what I used to think

[@cocadda1067]

Loved it......

[@vishnuteja4964]

Sir I'm from India

[@abhisheks5938]

Can you take up 'enthalpy' in next video?

[@marcochimio]

I get the impression that chemists prefer the + convention, because they (we, in my case) like to think of heat and work as both coming FROM the system, especially during chemical reactions that can generate both. On the other hand, engineers (and a lot of physicists) seem to prefer the - convention, especially when they are considering heat going into a system (like an engine of some sort) that results in the GENERATION of work. Potato-pototto.

[@Ottmar555]

I looked up a couple books, and mechanical engineers do prefer the - convention. I am a chemical engineer, so also like the + convention.

[@projectmanager3532]

Can you do law of radioactivity

[@projectmanager3532]

Please

[@DrDeuteron]

The law of a radioactivity is that an unstable atom does not age. If you make a fresh brand new U238 atom in a reactor today and it is 1hour old, it is identical in every possible way to one that his been in the ground for 4,000,000,000 years that I dig up and place next to it. Think about that for a while, and you will able to derive everything you need to know about radioactivity.

[@projectmanager3532]

@@ishanmukherjee5194 yes

[@projectmanager3532]

@@ishanmukherjee5194 thanks man

[@tulio829]

Question: based on this context. Temperature is part of the internal energy. Or a measure to describe the internal energy?

[@miromar3055]

Brilliant.... Could you please mention the software u use to write text, it seems handwritten.. also the animation part... I shall be grateful

[@Tom-sp3gy]

Brilliant 👏

[@darrellrees4371]

Would it be correct to think of the first law as establishing an equivalence between work and heat for a thermodynamic system (perhaps among other things) in much the same way as the work energy theorem establishes an equivalence for work and kinetic energy for a mechanical system?

[@narendranathmaji1512]

Sir I think in Q = DeltaU + W, here W is the work by external forces( like external pressure,etc.) and Work by gas has already been included in the change in internal energy because of work energy theorem. Sir am I correct??

[@HolidiumLabsTHUNDER]

I broke the laws of thermodynamics and Im proud to say Im not in cuffs. Quantum laws changed everything and for 18 years my products have never failed.

[@hossainboard86]

Pls give me!!! online lectures of physics!!!!

[@notsosmart3288]

You’re the best

[@Draginx]

I love parth's videos! I have been with your channel for over a year now and Im thinking about signing up for your patreon! Whats on it? Also, where can i buy the physics shirt you showed on the community post?

[@ParthGChannel]

Thank you so much for the support! My Patreon is a place for me to communicate with viewers and find out what videos they'd like me to make, as well as an avenue for me to answer questions about my video creation process + more. My top tier (Giga) patrons also get mentioned in my videos at the end! I want to work on offering more to my Patrons too, so suggestions are welcome! Shirts can be found on the "Store" tab of my channel, kzbin.infostore Thank you once again for the kind words and support! :)

[@Draginx]

@@ParthGChannel OFC! I love your videos and spring on them the second i get the chance!!!

[@rbrhbrfbg5458]

What it a particle quantum tunnels inside the system?

[@vishnuteja4964]

My friend name also parth he also so intelligent like u

[@nafisarman8266]

I'm waiting desperately for the oscillation vedio

[@sayandeeppal4730]

-w killed me at the first minute

[@yashrajdebnath5747]

I guess the change in thumbnail and video title is the effect of Veritasium's video 😅😄

[@Jehannum2000]

You played a later section of your outro music.

[@nafisarman8266]

Sir please make a video on oscillation. Please don't reject this request please please please please please please please please please please please

[@YuzuruA]

no jokes with Fight Club?

[@pashupatinathdutta4648]

Sir, this is for Physics or chemistry.There is a difference of sign in physics and chemistry.Regards.

[@nafisarman8266]

You don't have a single vedio on oscillation

[@asadislam9834]

First

[@tjk581]

Oh no, you kept the mathematics as simple as possible. Do you know anybody, who while explaining some law of physics keeps math very complicated?

[@deepanshuchouhan7110]

Fifth

[@JohnVKaravitis]

Please, no background music, it's annoying.

[@TheHumanHades]

No one who is commenting now has watched the whole video

[@davep8221]

tl;dw?

[@abhijithunni2976]

മലയാളി ആണോ 😕

[@HerrFunnybones]

I feel robbed

[@Ottmar555]

Why?

[@georgearabe]

i think he talks too much on what could be explained in a few words with few maths

[@introvertdimwit8623]

Are you an Indian?