2nd law of thermodynamics...?

Question

best, most complete, accurate, simple and concise explanation of this that will work down the pub?

Answer 1

That it is a dynamic thermal law, and you shouldn't question it becuase it'll burn your bum. Er, sorry, no clue, can't be bothered to look it up (neither can you, so you can't moan.)

Answer 2

The first law of thermodynamics states that energy is conserved, it cannot be created or destroyed. However this law gives no indication as to the direction of the energy transfer.

The second law of thermodynamics states that processes occur in a certain direction, not in any direction. A good example of this (for a good pub explanation):

"It is common experience that a cup of hot coffee left in a cooler room eventually cools off. This process satisfies the first law of thermodynamics since the amount of energy lost by the coffee is equal to the amount gained by the surrounding air. Now let us consider the reverse process - the hot coffee getting even hotter in a cooler room as a result of heat transfer from the room air. We all know this process never takes place. Yet, doing so would no violate the first law as long as the amount of energy lost by the air is equal to the amount gained by the coffee."

It is clear that "processes proceed in a certain direction and not in the reverse direction." So basically the first law states that energy mus be conserved and the second law tells you in which direction the process will occur.

Answer 3

Thermodynamics:

1st Law. You can't get something for nothing

2nd Law: You can't get it cheap either.

For a CLOSED system, given no external inputs of energy, that system will always move towards a state of randomness. The first law says you cannot get any useful work without expending an equal or greater amount of energy. The second law says you also HAVE to generate randomness, which can be heat, disorder, etc. Which means that while the first law allows you to expend an equal amount of energy, the second law says you also have to use energy to create order, and that energy can be substantial.

To get useful work the first law says you have to expend energy. The second law says you also have to account for heat and randomness. Therefore, to get useful work, you always have to expend more energy than you will gain from useful work. That is essentially the 2nd Law.

BTW, this is only true for CLOSED systems. The Earth, which gets energy inputs from the sun above and nuclear decay below, gets far more energy inputed onto the surface than is expended by maintaining life. That's why people who use the 2nd Law to discredit evolution are total morons. The Universe, however, should be a closed system by definition.

Answer 4

1. It is impossible for any engine cycle to convert all of the heat supplied to it into work.
OR,
2. Heat will not flow from a cold to a hot body unless compelled to do so by the application of an external agency.

Although the above statements appear, at first sight, to be quite different, they are in fact corollaries of the same law. There are other versions too but they are likely to be less suitable to an airing at the pub!

Answer 5

Well, I actually like one of the other answers better than mine. It was the one about coffee cooling off. But I would add something to it.

Heat death of the universe. The only way to generate usefull work is to have hot coffee cups cool off. It takes more energy to heat up the coffee cup than you can recover by cooling it off. So eventually every thing in the universe will reach the same temperature and there will be no heat transfer.

Answer 6

The second law of thermodynamics.
Entropy.
All things tend toward disorder.
Without the constant input of energy to counter entropy, all things fall down or become messy.
Example: Paperwork. If energy is not expended to keep paperwork in order it tends toward the appearance of the aftermath of a tornado. A stack of rocks will eventually fall down without energy expended to maintain its order/structure. An old house falls to ruin if untended over time.
Anything with potential energy, the rock at the top of the hill, will tend toward zero potential energy, eventually the rock will end up at the bottom of the hill where its potential energy is zero or near zero.
Entropy: All things tend toward disorder. It takes energy to counter the effect of entropy in order to maintain order.

Answer 7

any process which moves energy from one place or form to another place or form will convert some of that energy into waste heat energy. It's considered to be one of the most important concepts in physics and in some ways it defines the direction of the flow of time - time goes forward in the direction that the law holds true.

Answer 8

Processes in real life have a certain direction. For example: Heat doesn't flow from cold to hot without work being done to make it so.

Answer 9

It comes after the first law and just before the third law

Answer 10

The three laws of thermodynamics

1. You can't win, you can only break even.
2. You can only break even at absolute zero.
3. You can never reach absolute zero.