Entropy - By MITK12Videos
Transcript
| 00:12 | mm . Have you ever noticed that your room only | |
| 00:17 | gets messier over time ? Well , guess what ? | |
| 00:21 | Everything in the universe works the same way . Things | |
| 00:23 | only tend to get more disordered on their own . | |
| 00:26 | For instance , let's look at this video . Can | |
| 00:28 | you tell which side is played forward and which is | |
| 00:30 | played backward ? Oh yeah , that's easy . The | |
| 00:33 | balloon is exploding . But did you realize that things | |
| 00:35 | got more disordered during the process ? The molecules of | |
| 00:38 | water went from a nicely organized balloon shape to random | |
| 00:41 | droplets flying out in every direction . And how about | |
| 00:44 | this one ? Which one is played forward ? The | |
| 00:46 | right one ? Everybody knows that orange juice doesn't assemble | |
| 00:49 | itself back into the pulp of an orange . All | |
| 00:51 | right . How about this last example then a chemical | |
| 00:54 | reaction involving three gases , nitrogen , hydrogen and pneumonia | |
| 00:58 | . Uh , this one is harder on hydrogen and | |
| 01:00 | hydrogen going to form ammonia or ammonia going to separate | |
| 01:03 | into hydrogen and nitrogen . Well , this one is | |
| 01:06 | not so obvious , but there is something that can | |
| 01:08 | give us the answer to these three situations . The | |
| 01:11 | reactions resulted in increased disorder and in physics we use | |
| 01:14 | the notion of entropy to represent the fact that things | |
| 01:16 | tend to get more disordered over time . To put | |
| 01:19 | it simply entropy is a measure of disorder . But | |
| 01:22 | what do we mean exactly by disorder ? Let's consider | |
| 01:25 | this free days being randomly shaken . And let's look | |
| 01:27 | at the some of the numbers on the dice . | |
| 01:30 | For example , if we visit right now , the | |
| 01:32 | sum is four plus 37 plus 5 , 12 . | |
| 01:35 | We will call that the state of the system and | |
| 01:38 | we'll use it to illustrate the notion of order . | |
| 01:40 | For example , if the free day is also one | |
| 01:43 | , then the state is free . Note that there | |
| 01:45 | is only one way to obtain the state . Old | |
| 01:48 | ice must be showing one by comparison . There are | |
| 01:51 | three possibilities to get into ST four . This state | |
| 01:54 | has less orders and state free because the dice could | |
| 01:57 | be in any of these combinations . And the state | |
| 01:59 | was still before . Now there are six combinations of | |
| 02:03 | the dice that result in the state five . This | |
| 02:06 | state has less older than the previous state because the | |
| 02:08 | dice could be in any of these six options and | |
| 02:10 | the state would still be five . This example illustrates | |
| 02:13 | the notion of disorder . The more possibilities there are | |
| 02:16 | forgiven state and the more disordered the state is here's | |
| 02:20 | a plot that shows the number of combinations as a | |
| 02:22 | function of the state , The maximum for 10 and | |
| 02:25 | 11 , which can each be achieved through 27 possible | |
| 02:28 | combinations . For example , this shows all the combinations | |
| 02:32 | that result in the state 10 . This is the | |
| 02:35 | state of highest disorder . Okay , so why is | |
| 02:38 | it useful Because it tells us how our experiment is | |
| 02:42 | more likely to evolve . In fact , as the | |
| 02:44 | days change randomly , they're more likely to produce the | |
| 02:47 | 10 or 11 than a free on 18 because 10 | |
| 02:50 | or 11 are much more disordered states . You can | |
| 02:53 | see here that the state jumps a lot , but | |
| 02:55 | that's because we're only using three dies . Now . | |
| 02:58 | If you imagine that we have 100 of these days | |
| 03:01 | , starting from the situation where the also wants , | |
| 03:03 | then this is how the state would evolve . The | |
| 03:06 | dies quickly moved away from this very older state . | |
| 03:09 | And over time the system naturally evolves towards the state | |
| 03:12 | of highest disorder . Now , let's take a second | |
| 03:15 | look at the analogy with the tidiness of your room | |
| 03:18 | . The ordered state is the state in which every | |
| 03:20 | object is in its correct location . For each object | |
| 03:23 | . That is not the correct location . The room | |
| 03:25 | is more disordered , just like our dice . There | |
| 03:27 | are a lot of configurations in which the room would | |
| 03:29 | be as disordered are equally messy . This would be | |
| 03:32 | the state of highest disorder , and over time the | |
| 03:35 | room naturally tense at the state of highest disorder . | |
| 03:38 | Finally , let's see a practical example where entropy helps | |
| 03:40 | us understand the direction of a reaction . If you | |
| 03:43 | put some ice into a glass of water and leave | |
| 03:45 | it to sit , all the ice will melt , | |
| 03:46 | of course , you know this because the water is | |
| 03:48 | warmer than the ice , but what exactly is happening | |
| 03:51 | at the molecular level ? The molecules in an ice | |
| 03:53 | keeper , tightly packed together into a highly ordered lattice | |
| 03:56 | molecules inside a solid do move around , but not | |
| 03:58 | very much . This is why the ISIS . Cold | |
| 04:01 | water is a liquid and has a higher entropy molecules | |
| 04:04 | in the liquid move around a lot more freely , | |
| 04:06 | which is what allows liquids to flow . Water molecules | |
| 04:09 | bounce off the ice molecules given them energy and the | |
| 04:12 | ice begins to mount colder water has a much higher | |
| 04:15 | entropy than the warm water with ice , Although technically | |
| 04:18 | nothing physically prevents all the molecules from spontaneously forming an | |
| 04:21 | ice cube at the molecular level . This does not | |
| 04:23 | happen because of anxiety , just like our dice , | |
| 04:26 | there are many more ways for H20 molecules to arrange | |
| 04:28 | themselves in a glass of water than for the same | |
| 04:30 | molecules to arrange themselves into an ice cube . This | |
| 04:33 | is why heat always flows from a hot body to | |
| 04:35 | a colder body . So now you can appreciate how | |
| 04:38 | entropy informs us about the evolution of physical processes . | |
| 04:41 | Entropy is a fundamental notion in science because it is | |
| 04:44 | central pillar in firmer dynamics , which allows us to | |
| 04:47 | understand everything from air conditioners to jet engines . In | |
| 04:51 | fact , entropy helps us to understand the universe at | |
| 04:53 | all levels . From a simple system of three dice | |
| 04:56 | to billions of stars and Galaxies , entropy gives us | |
| 04:59 | the direction of the hour of time . No matter | |
| 05:01 | what we're observing , we can be almost certain that | |
| 05:03 | the entropy of the universe is increasing . Yeah . |
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