Entropy intuition | Thermodynamics | Physics | Khan Academy
ฝัง
- เผยแพร่เมื่อ 26 ก.ย. 2024
- Courses on Khan Academy are always 100% free. Start practicing-and saving your progress-now: www.khanacadem...
Introduces second law of thermodynamics. A discussion of entropy change in terms of heat and microstates . Created by Sal Khan.
Watch the next lesson: www.khanacadem...
Missed the previous lesson? www.khanacadem...
Physics on Khan Academy: Physics is the study of the basic principles that govern the physical world around us. We'll start by looking at motion itself. Then, we'll learn about forces, momentum, energy, and other concepts in lots of different physical situations. To get the most out of physics, you'll need a solid understanding of algebra and a basic understanding of trigonometry.
About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.
For free. For everyone. Forever. #YouCanLearnAnything
Subscribe to Khan Academy’s Physics channel: / channel
Subscribe to Khan Academy: www.youtube.co...
you just disproved it and you deserve a noble prize. lol
Awesome! Just one thing. Del S =Q/T only when the process is reversible! This is quite important I believe. We cannot write this for the actual heat exchanged if the process is not reversible but rather we should find the heat exchanged in its equivalent reversible process......Also I think you should add the entropy change of the air-conditioner to the mix as well.
It's always nice to see someone explaining entropy as well as khan =)
there is a high pitch sound when i play this video.
I didnt like it at all
This definitely helped :D
I have a question- Energy wants to spread out but matter seems to wonna clump together because of gravity. So is gravity reducing entropy from the Universe(because it makes order too)? And If it is then it might be giving out entropy in some way. Right?
vinod kumar bcoz gravity act as an external work to compress the material....and this external work make the entropy chane positive.....and again entropy increase....
@@pankajkumarpal1183 so the "force" of gravity, the most inherent influence of mass-energy-tensor on spacetime itself, is an external source?
Energy is also a cause of curvature (just like pressure, shear, stress...):
Mass/energy tells spacetime how to curve, which then tells mass/energy how to move. To paraphrase a quote
Awesome video about entropy and it cleared up my misunderstanding about entropy. We have to consider conditions, such as pressure, temperature, volume, and the number of particles in the system to evaluate the entropy of the system. The presentation in the video is amazing because it incorporates the definition of entropy that applies to thermodynamics and real-life applications, as well as connections to statistical mechanics at least at the fundamental level.
Entropy Owns Every stupid "Free Energy" video on TH-cam. Thanks khanacademy!
The most depressing law ever discovered: The 2nd Law of Thermodynamics.
the clean and dirty room example shouldn't be taken so literally, it is actually quite a great way to explain entropy metaphorically.
You my friend, are officially the Keanu Reeves of test taking.
Isn't the equation with capital omega on Boltzmann's gravestone in Vienna?
Thanks a lot! I have a final exam on thermodynamics tomorrow, that pretty much clarified myn thoughts.
My mind is blown especialy by that sound in the background😕
Exactly, metabolism gives heat for cells to use as work -> less entropy inside body due to ordered work -> heat not used as work discarded outside increasing outside entropy more than decrease of entropy inside (by 2nd law).
@jesusgarciab Entropy is directly related to temperature, since temperature measures the average inernal kinetic energy of the molecules.
Holding volume and pressure constant and increasing the temperature, you get the following: an increase in internal molecular kinetic energy, an increase in the distribution of micro states, an increase the entropy.
...just watch a few of this guys videos...10000000x better than anything on tv
Brilliant Sal, I've been trying to understand Terence McKenna's Entropy curve and while i'm no genius, i think i'm getting the hang of this.. Go raibh maith agat, mo chara :-)
The most simple and straightforward explanation of Entropy is this:
Take 2 planets.
Pause time for both planets.
Resume time for planet 1 and leave planet 2 in pause.
After 100 years, compare planet 1 and planet 2.
Planet 1 after 100 years had more tides, earthquakes, rock fallen, etc... and nothing happened in planet 2 because it was paused.
Thus entropy is in planet 1 is higher than planet 2.
Entropy="Things that happen"
And because 'stuff' will always happen entropy always increases.
Well, when you clean the dirty room, you usually end up throwing some stuff in the trash and then you vacuum, so there is literally less matter in the room, so I guess there would be less entropy in the room at the end ; ) Also, it seems to me that there are few possible states that we can call clean, while there are many many possible states that we can call dirty, so the dirty states are more probable.
Great video Khan Academy, thanks so much, keep up the good work.
Super helpful video, just finished an assignment the night before it's due XD didn't understand this stuff til now.
what the professors equating entropy to disorder- applied to your room- are really saying is that there are more states in which a room is dirty than there are states in which a room is clean.
This video should be renamed as Entropy for Creation Scientists!
Me at 16:18 when all the molecules bump into each other, perfectly popping the ball up several feet
The Entropy Law of TH-cam says the number of commenters that think like @ 6:15 can only ever increase, never decrease. 'I have just disproved the Second Law, I deserve a Nobel Prize'.
Thank you man!! a lot!!
dude you definition at 9:15 is GREAT...just the best thank you!!!
the example of the messy room is good if looked at the right angle. What it means metaphorically is that it takes less energy to let a room get dirty than to always keep it clean, therefore its favored by the law of thermodynamics. The whole idea is that the world always wants to take a form with less energy. Another good example is a piece of wood, it burns early because in order for it to remain in tis solid state it take a lot of energy,so by breaking into ashes and releasing heat is favored
I was just thinking of the opening scene of the movie Scanners when that guy's head exploded. If it not been for the second law of thermodynamics, those bloody chunks could reassemble to form that guy's head. That would be about as likely being able to make a guy's head explode using your mind :)
This is probably the most clear explanation I've ever seen. Good job.
You guys do a magnificent Job.. Thank you!
I lol'd so hard at 15:27
@Deicidead This example is a little over simplified. Skip to 8:13, the tells you what is and is not Entropy. Rocks falling is not necessarily entropy.
Always yours Video can guide us with presentation to conclusions! Brilliant!
Good that you mention entropy from first equation. Entropy as you say is a big variety of physical interpretation the statistical disorer of the system but for our purpose of the system, but for our purpose to be just property of system like ENTHALPY or TEMPERATURE. Entropy can be used in many disciplines. If you look accustic it is one of the most studied field in 21st century encompassing underwater acustic, civil engineering acustic, enviromental climate acustic or signal acustic. With the applications of entropy and information theory in acustics many problems have been solve or improved. We apply the CHEBYSHEV-GALERKIN and CHEBYSHEV - COLOCATION spectral methods to directly solve the two dimensional Helmhaltz model equation. Also we have term of entropy the various irreversible prosess we have in the HYDRAULIC CYCLE.
Like you say we can imply entropy "like the room"!
Thank you for have your second content in mine "study book"
To figure out entropy you must analyze if the interaction between the objects is spontaneous or nonspontaneous. The nonspontaneous will require energy and therefore disrupt the other systems molecules. According to the 2nd law of thermodynamics, a cheetah for example will consume a gazelle in the form of chemical energy but unfortunately the energy stored will be little used as kinetic energy but it wasted in the form of heat.
Yeah this is good, people dont want to admit it sometimes but almost everything in Life, the World, and Universe is moving towards Disorder, Chaos, Dissolution, and eventually Death, in some ways , People might still have free will or whatever they call it but everything is kind of Aging, Breaking down, and going towards Death
how are you compressing the gas? in the free expansion of gas, you are adding heat to increase the kinetic energy of the molecules, which applies pressure on the container and expands it.
if you are allowing the container to freely contract, you are taking heat out of the system and decreasing entropy.
im not sure what to think if you are compressing the gas by adding an external force, you are not changing the enthalpy because there is no transfer of heat to or from the external environment.
So in \delta S = Q /T is delta with respect to time? any system will reach equilibrium over time so suppose to such a system not at equilibrium we add a very small basically zero amount of heat over time wouldn't the change in entropy \delta S be non zero as the system is approaching equilibrium but Q/ T be essentially zero? so wouldn't this be violated
@WannaBDesi First of all the entropy increase is called the translational entr. increase (more space for the molecules to occupy hence more "disorder") and similarly when the gas compresses its translational entropy goes down. If both processes are done in a reversible manner (i.e. infinitely slow) than heat is allowed to enter/leave the system and the temp. would stay constant. Doing it fast (using a bycyclepump,etc.) means the surroundings cannot supply all the heat so the temp will change
the way i imagine it, is energy itself is centralized and it is becoming more and more dispersed. at the big bang it was all close together and it is spreading out
I wish this guy was my thermodynamics lecturer instead of my current one
for the water it is - the heat from the water had to go somewhere however, increasing the entropy of the universe. also, you have to do work to freeze water, hence increasing entropy further.
please answer my query
the process in which entropy of an isolated system decreases does not takes place,
then how the adiabatic compression is possible in carnot's reversible cycle?
plzzzzz answer fast
Damini Diwakar you are talking about energy outside the system. The heat , or work require to do carrnot cycle must be counted, that will make the 2nd law correct
@WannaBDesi if we are dismissing temperature, then the entropy of your system would dicrease. BUT at expense of some other factors that will increase the total entropy, just as the AC example.
the drawing with the molecules looks like a collection of genders people identify by
Thx a lot.
@crankspider But if there is still a heat (reservoir) after thermal equalibrium, and the one side goes colder, the second law would have to move the heat to that cooler resevoir, how would you write that in a math formula?
Sal,
Everyone knows the 1st law, but few know the 2nd.
I think of the 2nd law: "the ability of heat to do useful work become irreversibility diminished as temperature drops".
Thanks you, that video helped me a lot.
Thank you for this very clear explanation Sal !!!
I'm not really okay with the example given about the dirty room, I think actually the dirty room has more entropy in a practical way, since a clean room has less stuff than a dirty room, a dirty room has more "objects" or molecules than a clean one, let be a clean room with 1000 objects in, versus, the same room in the same state with added dirt "added objects" all around, there is absolutely a lot more possibilities to rearrange the "1000objects+dirt" filling the dirty room. this means in Boltzmann formula S=k.ln(Wi), Wi(dirty)>Wi(clean) so S(dirty)>S(clean). The arrow of time applied to a clean room tells us that a clean room will evolve in time to enter a dirtier state! the clean room evolving in time is less likely to get spontaneously cleaner.... as a matter of fact the most probable state for a clean room left to evolve spontaneously is a dirtier state more entropic with a minimal energy, this tels us the fact that if you let a clean room evolve let's say for a million years with a chair, some concrete stuff, roof ...etc in it, checking it out if you live long enough lol! you're likely to find it full of dust with half of the roof down with even some elements decomposing, and full of bacteria and once again (Wi) number of complexion increases S increases, this room would've evolved closer to its equilibrium getting more dirth less energy. getting back from your summer holidays you'll always have to clean the dusty rooms you've left all clean.
If there was no energy in the form of wind, much less dust would get into the room...
8:10 shouldn't it be -Qe/T2?, Since heat is leaving the engine. And doesn't that again disprove the second law?
No because you are taking about the outside gaining the heat hence potive Q over outside temperature
No, you should refer to the heat absorbed by the outside (hence what T2, the denominator, is referring to).
I think there should be a -Q/T3 where T3 is the temperature of the engine.
I have a simple question (I'm a beginner in Physics) : Following the 1st law: Does the Temperature keep constant in the universe in the way heat does???
Thanks.
Mentira
No. Work changes the temperature.
Ellie Lyndon, that work is being done by dark energy. Which is considered as the reason for the expansion of the Universe.
vinod kumar what is the universe expansion? Sorry i am just begginer
@illisanantexico The universe could never have started from order, then there would be an infinite number of causes before it. You can get a complex system from a simple system, but you can't get a simple system from a complex system. That's what the 2nd law implies. As in, the less entropy in an event, the less 'cause' it needs to exist. Evolution started from extremely simple organisms, that evolved into more complex organisms, and it's already an observable thing. Hope i cleared things up!
the 2nd law of thermodynamics basically states that "Nothing lasts forever" but I'd like to take a philosophical jump here and note that, that statements means two things.
1. All existent things will eventually end
2. Nothing (the lack of something) always persists
I don't know if this is just pointless jibber jabber but if its not it may point to reason to believe that nothing exists and all existence is an illusion. Plus all things had a point of inception, so where did it all come from?
agreed. although information can be thought of as negative entropy. dna is a form of information. but like you implied, thermo first and second law.
very helpful video. thanks for posting it.
Could someone please explain the difference b/t the Q and T values?
luvisacigarette8 what's there to explain? Q is the amount of energy in form of heat that is moving from a state to another, like the air conditioner example. T is just the temperature of each state.
Lets apply entropy to life!! delta S >= all the B.S. you go through in your life!!! ^.^ Deep!
Another great vid, thanks a lot!
for thermal equilibrium, entropy should b same?
There was a time when that creature was perfectly suited to survive in it's inherent state, however time and happenstance required that it also change with it's environment to keep up or it would become obsolete.
Entropy means the ball WON'T shoot into the air, not that it's improbable; it doing so would be an decrease of entropy for the system. Assuming an equal probability for all states means the ground molecules' states would never be so evenly distributed as to push the ball upwards. 2nd law of therm. says it can't happen, if you want to argue that it could theoretically happen then you need to argue for why the law isn't valid in some fringe case, maybe because of assumptions made in its derivation
Is it possible to move energy again after the 3rd law of thermodynamics, once it reaches thermal equilibrium with three states of matter?
Pretty well explained
I think your vids are awesome, but you seem to have an undying love for the colour magenta ;)
Great video.. But, I am confused at the example of heat transfer, which you can find in almost all the textbooks, and computation of the entropy: The heat transfer at temperature difference is an irreversible process, how can you justify that the change in entropy is equal to Q/T_1 and Q/T_2? Or am i making a fundamental mistake?
Thank you for that!
Superb video
I wish i watch this before my thermal mid term exam >.
i watched this on shrooms and it blew my mind
entropy and the future of chaos !
amazing even after 14 year
Is there an objective definition of ordered?
@mekbarbie Q stands for energy transferred as heat.
so the number of possible physical energy states of nature must always increase.
Thanks sir
I'm not getting about entropy. should i die now?
entropy must breach the threshold of the universe in which it occurs?
my room being dirty is definitely the equilibrium state
Why it is that sometimes living organisms convert chemical substances into highly organised structures, such as cells, wouldnt this go against the second law of thermodynamics, which states that the entropy of universe must always increase as a result of a spontaneous process (a transition from order to disorder)?
Entropy is pudding-proof that the universe started from order. The universe did not appear by random happenstance and morph from disorder into order. It's preposterous. Entropy also says that the "younger" an object or system is, the more perfect it is. Which also defies evolution. Adaptation is not the idea of something perfecting itself, it is simply the result of a creature rolling with the punches so to speak of "things happening to it."
Everything was okay except the ball analogy wasn't clear at all.
@illisanantexico You are implying that evolution decreases the overall entropy. In fact, evolution generates entropy overall although it tends to decrease the entropy within the self-replicating system. Evolution is in no way a defiance of the laws of thermodynamics, as creationists seem to so often state. Also, a low number of states is not synonymous with perfection.
on hot side temperature is high in term of heat, and compressor changed its dirction..
nyc video..
but i have a doubt..
when i asked my teacher about the air conditioner example..he said that this law is only applicable for spontaneous processes...i. e. natural processes...n so AC's example is not applicable..
please explain...
I'l come to this when i am in university sal..
Now are you in University
so what is the inner energy?
simp
Entropy of a system can decrease if entropy of the environment increases.
gr8 video
Actually "disorder" is not a very good way to describe it. If you look at newer books they have moved away from the term. It was used by a scientist in the 19th century to try to describe it to laymen. It is a little better to describe it just as the dispersion of energy when it is allowed to do so. (not restricted)
Hello, I think Im starting to get this concept of entropy, so it is supposed to be an indication of how many states can a system have. I understand this with volume change, but how can we apply this for a change in temperature or pressure? can somone help me with an explanation "for dummies" lol
@dsac6007 indeed, in their wondrously condescending manner.
What about climate control in a car? Does that defy the 2nd law of thermodynamics aswell?
@vomaxHELLnO He stated earlier that T1 was "hotter" than T2. If he had said T2 was "hotter", then it would have been greater than T1.
Wow, now THAT'S HD....
where can i get some sample problem for this??
I think i got it, but i don't understand why heat/temperature = change in entropy
i wonder how hard he cleans his room if he raises the temperature a noticeable amount......
I want the history channel to explain this to me as if I am a child.
Hot body to cold body
Because the Heat leaves the hot body at higher temperature the value of entropy is smaller and negative
And
Because the heat enters the cold body at lower temperature the value will of entropy is higher snd positive.
The sum of the entropies is positive.
Cold body to hot body
Heat transfer from evaporator to condenser.
Evaporator is the colder body
&
Condenser is the hotter body
Heat leaves colder body at lower temperature so the value of entropy is higher and negative
Then after the compressor the
heat enters the hot body at higher temperature so the value of entropy is lower and positive
The sum of entropies is negative?
I believe no
Because the enthalpy of the system still goes up in the compressor and the entropy change is positive in this process, thus making the sum of entropies > 0 ?