System and surroundings
Channel: Thermodynamics For Everyone
Date: 17/09/2021

This video goes through the concept of "system and surroundings".

In principle, this concept is quite simple. The entire universe constitutes the system plus surroundings. Within the universe, you carve out what you are interested in. How do you decide what you're interested in? Well, that's up to you, and up to the problem at hand that you want to solve. But once you know what you're interested in, then you have your system. Everything else in the universe is the surroundings.

Now, you can discuss different cases of the relationship between system and surroundings, and there are technical words for that. An "isolated" system exchanges neither mass nor energy with the surroundings. Mass means kilograms of different types of substances, for example. Energy means joules of the types kinetic, gravitational, and internal, for example. A "closed" system exchanges energy but not mass. An "open" system exchanges both mass and energy with the surroundings.

If you're interested in two things separately, you can tackle this problem by having system 1 and system 2 and their possible interactions. Both systems in turn are immersed in the common surroundings.