1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

1st law of thermodynamics./ Conservation of energy.

  1. Jun 2, 2012 #1
    Hallo,

    I understand in a system energy is transformed from one form to another... Although I'm wondering is it possibile to get more energy "OUT" as in?

    Imagine this simple equation:

    Ein = Eout

    Eout: would usually be less than "Ein" due to losses going for heat,frictions,sound,etc... I understand that so far. In 99% of our systems follow this way.However, what if there is a system that produced more Eout than Ein? Is that violating the two laws?
    Maybe were applying another source of "In" thats not present or shown obvious that increased the "Eout". Another source could alter the expected results maybe...

    If there are system or any examples of what im saying could you share some if possibile?
     
  2. jcsd
  3. Jun 2, 2012 #2
    No, or else you would get a perpetual machine of the first kind. A direct violation of the first law of thermodynamics.
     
  4. Jun 2, 2012 #3
    I doubt that. Mainly because perpetual machines claim to create "energy" out of nowhere. I said that you had another source applied in the "Ein" of the system that resulted in a higher output.

    I found an example of this here: solarfeeds.com/mit-scientists-create-230-efficient-led-bulbs/ (Don't forget the www. I didn't added it because for some reason here is a problems)

    They used another source other then "electricity" to boost the output of that system
    Whereas perpetual motion machines are impossible because they "create" energy and THAT is a direct violation of the laws of both thermodynamics and conservation of energy.

    *For everyone... I've noticed that perpetual motion machines, over-unity claims, etc... are all forbidden in this site and I DO NOT INTEND ON TALKING ABOUT IT on this topic rather clarifying a thought in my mind.*
     
  5. Jun 2, 2012 #4
    By definition no, because if a system were ever to output more energy than it consumes, we would simply define a new set of potential energy so that total energy would again become conserved.
     
  6. Jun 2, 2012 #5
    An example of what I'm trying to say is friction. Its a contact force present in our daily lives right? While I'm typing on my keyboard I'm experiencing it. Does it destroy energy? No. Thats a violation of both laws but its reducing my energy... Thus resulting in energy loss to heat, sound,etc...
    Another example throwing a ball up in the sky then it falling down, is it falling at the same rate as thrown up? No. Why? Air resistance and we go on.
     
  7. Jun 2, 2012 #6
    Why would the system consume that additional energy output? Is it necessary to define a new potential energy? Maybe that energy is directly outputted and conserver in another form.
     
  8. Jun 2, 2012 #7
    From another related article "... it appears to draw in heat energy from its surroundings instead."
    There you have it. You cannot create energy out of nowhere.
     
  9. Jun 2, 2012 #8
    Alba_ei, you really need to re-read what I've written properly.
     
  10. Jun 2, 2012 #9

    Doc Al

    User Avatar

    Staff: Mentor

    Every example you gave satisfied conservation of energy. What's your point?
     
  11. Jun 2, 2012 #10
    Ah, Thats it. The simple comfort of satisfaction, I needed to know I was on the right track. One more thing though...

    What factors can effect energy other then force?
    Friction is a force and it causes energy loss what else causes a loss of energy other than force?
     
  12. Jun 2, 2012 #11
    It doesn't matter. If anything were to output a net increase in energy (output - input) even if one or both are zero or negative, we would simply define a new set of potential energy in such a way that by definition, total energy is again conserved. Because people don't like it when something is not conserved, so they tend to modify theories so that total energy would Become conserved. In the end it's just a matter of convention.



    Friction does not cause a loss of energy; it transforms and redistributes it. Ultimately energy is quantified by motion + "potential" motion.
     
  13. Jun 2, 2012 #12
    Hello hopeful, I note that this is your first post at Physics Forums and than no one has offered a welcome so let me first correct that omission.

    Welcome to Physics Forums, there are some really good members here.

    First reading your opening post I did at think that you were proposing a perpetual motion machine.
    However reading it more carefully I came to the conclusion that you realised that something was not right about that idea but were not sure what so was seeking guidance.
    I am guessing that you are meeting this subject for the first time.

    Basically any conservation law can be expressed by the phrase

    Input = output plus accumulation

    In your case you are rearranging this to

    Input minus output = accumulation

    and find that the accumulation is negative (ie decreasing)

    That is perfectly satisfactory for a system that has an internal store of energy that it calls upon to satisfy the difference.

    If that internal store is large the process can go on for a long time.

    A real world example would be a gas turbine where the input energy to the compressor stage is less than the ouput shaft energy, the difference being supplied from the stored energy of the combustion gas.

    Nothing above suggests perpetual motion, yours was actually a perceptive question I hope you do well in the future.
     
    Last edited: Jun 2, 2012
  14. Jun 2, 2012 #13
    Huh, never though it in that way.


    Thanks for the welcome Studiot.
    I might have sounded as if I wanted to propuse a perpetual motion machine but really I was not. I read about it a few times was not interested because it does not make sense so I buried it. However, I love studying about energy and the forms of conservation from one form to another its stunning to me. Understanding it more and more lead me to ask theses questions and thankfully knew I'm on the right track. I read a few post before this one to understand energy even more and lead me to a question: If we were able to create systems with 100% efficiency thats perfect but what if the result output was more?

    The answer to my mind was directly this: ERROR. But maybe it is not? Then the only rational explanation that came in my mind is something else played a role in that system. As you're compressor example was perfect and well rounded. Some stored energy played that role! Wonderful example.
    I thank you for that input and guidance it truly helped.
     
  15. Jun 2, 2012 #14
    You should compare this with a mechanical timepiece.

    You input mechanical energy when you wind it.
    This is stored in the spring or whatever.
    Then it is output again as the clock winds down although some is lost to friction, air resistance or whatever.

    In this case the only energy in the store is what is put in in the winding. There is no further internal store of chemical energy as in the turbine.

    So congratualtion on deducing that there must be an internal store.

    This is formalised in the First Law as internal energy.

    Keep asking the questions.

    :smile:
     
  16. Jun 2, 2012 #15
    What puzzels me always is how "force" effects the systems outputted results doesn't it? I mean air resistance, frictions, etc...
     
  17. Jun 2, 2012 #16
    I guess thats a natural thing that goes around any physical system that has able work. Maybe its a counter effect to it or so...
     
  18. Jun 2, 2012 #17
    Thanks Studiot I appreciate it.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: 1st law of thermodynamics./ Conservation of energy.
  1. 1st law- thermodynamics (Replies: 19)

Loading...