Eli5 Can someone explain Entropy? Quelqu’un peut expliquer l’entropie?
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Entropy is a measure of the amount of energy in a system that is unable to do work.
When you have high air pressure on one side of a system, and low pressure on the other side, the high pressure air will flow to the low side, and you can use that flow to do work. Then the pressure is equalized and it can’t do work anymore. If you were then to put energy in to separate the low and high pressure again, that would take more energy than you could get out of it due to the fact that almost everything has inefficiencies.
Once you go through, extract the work, and then recreate the original conditions of the system, energy has been lost to heat, so you have less energy to do work with.
This is an oversimplified example, but I hope it helps:
Let’s say a fluid/gas in a container is cold, all the molecules will be at the bottom of the container (because it’s colder and denser than the air around). This means, the number of possible configuration (a configuration is basically a specific description of where each and every particle and momentum) fitting this scenario is relatively low. So that’s a relatively low entropy.
If you heat it up and the fluid/gas starts to have the density as the air, the molecules can be anywhere in the container, so there are many more possibile configurations compared to the previous scenario, therefore higher entropy.
If you keep heat it up and the fluid/gaz is now much less dense than air. All the molecules will be concentrated at the top of the container. So the number of configurations is much closer to the first scenario and so is the entropy.
Entropy is basically a measure of how many different configurations can describe a specific scenario.
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