The Second Law of Thermodynamics!....help

Discussion in 'Off Topic Chat' started by Ccauceg, Oct 7, 2008.

  1. Ccauceg

    Ccauceg TPF Noob!

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    I have a paper to write that includes The Second Law of Thermodynamics. So I have been looking all over the web for a simple explaination of the law, and i cant seem to find one. Could someone please explain it in a way that a moron could understand?
     
  2. LaFoto

    LaFoto Just Corinna in real life Staff Member Supporting Member

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    Husband says "Easy, that one! Energies can change, but they always stay constant, there is no loss of energy in a closed system". He says that that is all there is to know about the second law of thermodynamics. (It's all Greek to me, anyway, so I can only repeat what he said - so don't add more questions to it - the only person in this household able to answer is going to fly to Barcelona in Spain in half an hour from now ...).
     
  3. spiffybeth

    spiffybeth TPF Noob!

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    entropy increases
     
  4. flygning

    flygning TPF Noob!

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  5. ferny

    ferny TPF Noob!

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    Friction, burns.
     
  6. Hertz van Rental

    Hertz van Rental TPF Noob!

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    Time heals.
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  7. ferny

    ferny TPF Noob!

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    THE LAWS OF ULTIMATE REALITY

    & Law of Mechanical Repair After your hands become coated with grease, your nose will begin to itch and you'll have to pee.

    & Law of Gravity Any tool, when dropped, will roll to the least accessible crevice furthest away from you.

    & Law of Probability The probability of being watched is directly proportional to the stupidity of your act.

    & Law of Random Numbers If you dial a wrong number, you never get a busy signal and someone always answers.

    & Law of the Alibi If you tell the boss you were late for work because you had a flat tire, the very next morning you will have a flat tire while running late for work.

    & Variation Law If you change lines (or traffic lanes), the one you were in will always move faster than the one you are in now (works every time).

    & Law of the Bath When the body is fully immersed in water, the telephone rings.

    & Law of Close Encounters The probability of meeting someone you know increases dramatically when you are with someone you don't want to be seen with.

    & Law of the Result When you try to prove to someone that a machine won't work, it will.

    & Law of Biomechanics The severity of the itch is inversely proportional to the reach.

    & Law of the Theater At any event, the people whose seats are furthest from the aisle arrive last.

    & The Starbucks Law As soon as you sit down to a cup of hot coffee, your boss will ask you to do something which will last until the coffee is cold.

    & Murphy's Law of Lockers If there are only two people in a locker room, they will have adjacent lockers.

    & Law of Physical Surfaces The chances of an open-faced jelly sandwich landing face down on a floor covering are directly correlated to the newness and cost of the carpet/rug.

    & Law of Logical Argument Anything is possible if you don't know what you are talking about.

    & Brown's Law of Physical Appearance If the shoe fits, it's ugly.

    & Oliver's Law of Public Speaking A closed mouth gathers no feet.

    & Wilson's Law of Commercial Marketing Strategy As soon as you find a product that you really like, they will stop making it.

    & Doctors' Law If you don't feel well, make an appointment to go to the doctor, by the time you get there you'll feel better. Don't make an appointment and you'll stay sick
     
  8. mrcrassic

    mrcrassic TPF Noob!

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    That's because there is no simple way to state the Second Law. There are two different texts to the law; Kelvin's text and Claussius's text (thanks, Wikipedia). It basically describes how entropy of a system increases approaching equilibrium.

    I think the simplest one is Kelvin's Text, which says verbatim: "It is impossible to convert all of heat energy into work." This implicates that there must be some other area of a system where heat energy will be dissipated. This is the premise behind a heat pump (the core of refrigerators, freezers, air conditioners, and anything that moves air from one temperature to another).

    As an aside, the efficiency of an engine (i.e., how well it handles dissipated heat) is compared to that of a Carnot Engine, or a theoretical engine with 100% maximum efficiency. This is impossible to create, but the closer the engine is to this theoretical upper limit, the more energy the engine saves, since less heat is being wasted. Most good engines (heat pumps, in this case) have somewhere between 80 to 85 percent maximum efficiency, which is really good.
     
  9. monkeykoder

    monkeykoder TPF Noob!

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    The maximum efficiency of of the Otto cycle is determined by the compression ratios at a 1:8 compression ratio it works out to a maximum efficiency of approximately 25% (last time I did the calculation for a physics class... Chew on that next time you're out driving.
     
  10. monkeykoder

    monkeykoder TPF Noob!

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    Don't forget that is the calculated MAXIMUM efficiency.
     
  11. mrcrassic

    mrcrassic TPF Noob!

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    This may sound unrelated, but considering that a road racing cyclist usually has an efficiency of about 23%, it makes sense.
     
  12. monkeykoder

    monkeykoder TPF Noob!

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    I would expect the efficiency there to be much greater. However there is some relationship with the whole rubber tire thing but given that the rubber tire limits efficiency to like 40% (I don't remember the numbers exactly) (this would give the person walking approximately 60% efficiency which sounds reasonable) that actually limits the efficiency of a car to 10% overall. My numbers may be off and they may have moved to a more efficient engine design that I'm not aware of but that does give an idea about the workings of the second law of thermodynamics (the systems tendency towards disorder) being somewhat proportional to the complexity of the system. Fun stuff.
     

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