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# Second Law of Thermodynamics

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The Second Law of Thermodynamics can be rephrased in several ways. Fundamentally, it says that heat always flows from hot objects to cold objects (unless work is exerted to make it flow the other direction). It can also be expressed using the concept of entropy as saying that the system's entropy will always naturally increase if no work is exerted to decrease it. These rephrasings mean fundamentally the same thing because heat deals with kinetic energy and increasing a system's kinetic energy will increase the system's entropy.

Second law of thermodynamics simply stated this just says that heat always flows from hot objects to cold objects never from cold objects to hot objects so if I take some sodas and they're warm and I stick them in an ice cooler full of ice, the cold doesn't go from the ice into the can, the heat actually goes from the ha- cans into the ice and warms up the ice thereby making the cans colder so it's the heat always goes from hot to cold never cold to hot.

We can extend the second law of thermodynamics so and talk about transfer of energy, remember the first law of thermodynamics says energy can never be created or destroyed but it can be converted from one form to another and sometimes we'll talk about the second law of thermodynamics as when energy is converted from one form to another, there's always going to be some wasted or it's going to be converted from a more useful form to a less useful form and typically that less useful form is heat so example in Physics if I've got work in and then that work is going to be producing some work like my fuel under my generator and that's producing electricity, the work in is going to equal the work out plus the heat because my generator is actually going to be producing a lot of heat and that's actually waste I can't use that heat for anything so the work in is always going to be greater than the work out because in any energy transformation I'm always loosing some energy in the form of heat to the environment and that's kind of what the second law of thermodynamics is all about.

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