Second Law of Thermodynamics

00:04:47
https://www.youtube.com/watch?v=YoekFxOizj4

Resumen

TLDRThis video by Mr. Andersen discusses the second law of thermodynamics, focusing on entropy—a measure of disorder in a system. Unlike the first law which states energy cannot be created or destroyed, the second law suggests entropy or disorder increases over time, particularly in closed systems. Examples of reversed and normal video sequences illustrate reversible and irreversible processes. The law posits that in an irreversible process, entropy increases, leading to a more chaotic system—termed as 'time's arrow.' While complex systems like computers are ordered, they are not closed systems, hence their order is balanced by disorder in their surroundings. Overall, entropy in a closed environment never decreases, aligning with the laws governing the universe.

Para llevar

  • ❓ Entropy is a measure of disorder in a process.
  • 🔄 Reversible processes maintain constant entropy.
  • 🚫 In irreversible processes, entropy increases over time.
  • 📏 Entropy is a state function, measured at specific states.
  • ↔ A process can be either reversible or irreversible.
  • 🔄 Videos illustrating entropy show order can only spontaneously decrease.
  • ⏱ Entropy is often referred to as 'time’s arrow'.
  • 🌌 Entropy of the universe will always increase.
  • ⚙️ Complex systems are not closed, thus maintaining order by increasing environmental disorder.
  • 📉 Entropy never decreases in closed systems.

Cronología

  • 00:00:00 - 00:04:47

    In this AP Physics video, Mr. Andersen explains the second law of thermodynamics, focusing on the concept of entropy, which is a measure of disorder in a system. The video discusses how reversible processes do not change entropy, while irreversible processes increase entropy over time. Entropy is likened to a state function and the concept of a lack of energy to do work, emphasizing its qualitative understanding in closed systems. Examples are provided using videos played in forward and reverse to illustrate entropy in reversible and irreversible processes. Despite seeming counter-intuitive, the increase of entropy in the universe accounts for the apparent order when considering the surroundings.

Mapa mental

Vídeo de preguntas y respuestas

  • What is entropy?

    Entropy is a measure of the amount of disorder in a process.

  • How does the second law of thermodynamics relate to entropy?

    It states that in a closed system, the amount of entropy will never decrease over time, indicating that disorder or entropy will increase.

  • What is a reversible process?

    A reversible process is one where the amount of entropy will not change and the process can go either way.

  • What characterizes an irreversible process?

    In an irreversible process, the entropy increases over time and the process cannot be reversed spontaneously.

  • Is entropy a state function?

    Yes, entropy is a state function, meaning it is measured at a specific state or point in time.

  • How does the video demonstrate entropy using examples?

    The video uses examples of videos played forwards and in reverse to show the difference between reversible and irreversible processes.

  • Does entropy decrease in a closed system?

    No, in a closed system, the entropy never decreases; it only increases.

  • Can the universe's entropy decrease?

    No, the entropy of the universe increases over time.

  • How is entropy related to the concept of time?

    Entropy is often referred to as time’s arrow because it indicates the direction of time in an irreversible process.

  • Why can complex systems like computers exist?

    Complex systems can exist because they are not closed systems; their order increases by making the surroundings less ordered.

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  • 00:00:07
    Hi. It’s Mr. Andersen and this is AP physics essentials video 133. It is on the second
  • 00:00:10
    law of thermodynamics. First law relates to energy and how it can neither be created nor
  • 00:00:15
    destroyed. But the second law relates to entropy. What is entropy? It is a measure of the amount
  • 00:00:20
    of disorder in a process. And so if you watch the word entropy I am increasing entropy of
  • 00:00:27
    entropy. In other words I am increasing the disorder. And it is much more likely that
  • 00:00:31
    it is to fall apart then all those pieces were to spontaneously come back together again.
  • 00:00:37
    So the second law of thermodynamics relates to processes that can either be reversible
  • 00:00:41
    or irreversible. Reversible means they can go either way. And the amount of entropy will
  • 00:00:46
    not change. But in an irreversible process the amount of entropy will increase over time.
  • 00:00:51
    Now entropy is a state function. That means it is just measured at one point or one state
  • 00:00:57
    in time. It measures disorder. Other alternative definitions, it is the lack of energy to do
  • 00:01:03
    work. And so a way to think of it is increasing chaos of the system or its organization of
  • 00:01:09
    the system. The nice thing about AP Physics is you do not have to quantify entropy. You
  • 00:01:13
    just have to know its quality, in other words what it is. In a closed system the amount
  • 00:01:18
    of entropy will never decrease. It always increases over time. And if we think of the
  • 00:01:22
    whole universe, the universe, entropy of the universe is going to increase over time as
  • 00:01:27
    well. Now that is kind of a vague concept. What does it mean to increase the entropy
  • 00:01:31
    of the universe. Let me give you some solid examples. And so I have two videos here. Video
  • 00:01:36
    A and B. Let me start playing them. They are both the same video but one is played in the
  • 00:01:41
    forward direction and one is played in the reverse direction. And so can you figure out
  • 00:01:45
    which one is forward and which on is reverse? It is hard to tell. If I remember right A
  • 00:01:52
    is actually played in the forward direction. So we can think of this as a reversible process.
  • 00:01:56
    It is just as likely to happen in the A direction as it is in the B direction. But let me show
  • 00:02:01
    you another video. Can you figure out which one of these is played in the forward and
  • 00:02:08
    which one is played in the reverse? Well you probably have never seen B as a video. You
  • 00:02:13
    do not see milk spontaneously move outside of a cup. So we know A is in the direction.
  • 00:02:17
    Now we are dealing with an irreversible process. It is totally probable to happen in the A
  • 00:02:22
    direction but it is statistically improbable if not impossible to happen in the B direction.
  • 00:02:27
    Let’s watch this. This is another one. So which one of these is in the forward direction?
  • 00:02:35
    Well B now is in the forward direction. So now we are getting at what it is to be an
  • 00:02:40
    irreversible process. In other words in an irreversible process, and I am just tugging
  • 00:02:45
    on the block at the bottom, it is moving in that direction. Now could the reverse occur?
  • 00:02:49
    Perhaps. But it is going to be statistically improbable for it to occur. So now we have
  • 00:02:55
    an irreversible process. What is going to happen to the entropy? It is going to increase
  • 00:02:59
    over time. And sometimes you will hear it referred to, entropy, as time’s arrow. It
  • 00:03:03
    is going to move in the direction of time in an irreversible process. Let me give you
  • 00:03:08
    an example of that. On the left we have gas molecules in a container. On the right we
  • 00:03:12
    have those same gas molecules in a container. So which do you think took place first? Which
  • 00:03:17
    of these is early and which is later in time? Well the right answer is going to be like
  • 00:03:22
    that. It is going to become more disordered in time. So what you can do is just draw the
  • 00:03:25
    arrow of time. And then entropy is just going to be in that same exact direction. And so
  • 00:03:31
    the second law of thermodynamics says in a closed system, a system isolated from its
  • 00:03:36
    surroundings, entropy will never decrease. In other words entropy is going to increase
  • 00:03:40
    over time. In other words in a closed system as time advances entropy is going to advance
  • 00:03:46
    as well. But this might see counter intuitive. How could I make something like this video
  • 00:03:51
    and this computer, they seem to have a huge amount of order. They do not see to be chaotic
  • 00:03:57
    as well. And so it seems like time and entropy in this case are reversed. Over time we have
  • 00:04:03
    something that is more complex. Well you have to step back again. And remember what I said
  • 00:04:07
    very carefully. Entropy never decreases but that is in a closed system. This computer
  • 00:04:12
    and this video are not a closed system. I made them more ordered by making the surroundings
  • 00:04:18
    less ordered. And that leads into this whole idea that over time entropy is going to increase
  • 00:04:23
    in the environment. And so did you learn to connect qualitatively the second law of thermodynamics
  • 00:04:28
    and the state function of entropy? I hope so. And I hope that was helpful.
Etiquetas
  • entropy
  • second law of thermodynamics
  • disorder
  • reversible process
  • irreversible process
  • state function
  • closed system
  • time’s arrow
  • universe
  • complex systems