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What exaclty is Mechanical Energy? Or more specificaly potential energy (the subset)

  1. Jun 19, 2012 #1
    Because i'm a bit confused...
    I know mechanical energy is potential energy and kinetic energy but I'm not sure of the exact definition of potential energy.
    Is potential energy (the subset of mechanical energy) the following?
    • Gravitational potential energy
    • Elastic potential energy
    • Chemical potential energy
    • Electric potential energy
    • Nuclear potential energy
    as it shows on Wikipedia - http://en.wikipedia.org/wiki/Potential_energy[/PLAIN] [Broken]

    or is it just the following?
    • Gravitational potential energy
    as the are saying to me on Yahoo Answers - http://answers.yahoo.com/question/index?qid=20120618063654AASSBFN
     
    Last edited by a moderator: May 6, 2017
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  3. Jun 19, 2012 #2

    PhanthomJay

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    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    Wiki gives a few good examples. Potential Energy is energy stored in a body or system by virtue of its position within a force field.
     
  4. Jun 19, 2012 #3
    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    yes but is it just GPE or is it others as well? That's the big question here. Because you could say chemical energy is energy due to the position of charges, right?
     
  5. Jun 19, 2012 #4

    Drakkith

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    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    Potential energy in general is all of it. You can have chemical potential energy, nuclear potential energy, etc.
     
  6. Jun 19, 2012 #5
    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    Now we're getting somewhere! So does that mean chemical energy is mechanical?
     
  7. Jun 19, 2012 #6

    Drakkith

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    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    I don't believe so. Chemical processes are described by quantum effects, so I don't think you would say they are mechanical. But I don't really know honestly.
     
  8. Jun 19, 2012 #7

    PhanthomJay

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    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    By definition, mechanical energy is the sum of the potential and kinetic energies of a body or system. Unfortunately, the term 'mechanical' energy is used in a completely different context, as in electrical energy converted to mechanical energy by a motor, or mechanical energy converted to electrical energy by a generator. Don't confuse the two definitions.

    By the first definition, where Mechanical Energy is the sum of the potential and kinetic energies, then Chemical Potential Energy is only part of the total mechanical energy of a system.
     
  9. Jun 19, 2012 #8
    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    OK so people normally (and unfortunately) use the term "mechanical energy" for something else. So then what is the real term for this "something else" for which it is normally used? Its a sort of organized kinetic energy... PhanthomJay?
     
  10. Jun 19, 2012 #9

    Drakkith

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  11. Jun 19, 2012 #10
    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    my previous question still applies.
     
    Last edited: Jun 19, 2012
  12. Jun 19, 2012 #11
    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    Potential energy means it will begin to move spontaneously in a particular direction if it is permitted to, but before it can move it may need a push, it may have to be released from captivity. Gravitational - it's on the shelf but with a nudge it will fall. Electrical PE - a charge may be confined in some way but if you remove the confinement then it will be spontaneously attracted or repelled somewhere. Elastic PE, a stretched spring is on a hook but it you slide it off the hook it will go boing. Chemical PE - a spark puts the dynamite "over the edge" and then a lot of motion will occur.

    It's considered mechanical energy because all kinds of PE are related to conservative forces, never related to nonconservative forces. The energy expended to put something somewhere can be recovered, and the form in which it is recovered is motion.
     
    Last edited: Jun 19, 2012
  13. Jun 20, 2012 #12
    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    OK i get it, chemical energy IS a type of mechanical energy. But now i'm wondering why so many people deny that, see my "yahoo answers" replies:


     
  14. Jun 20, 2012 #13
    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    !!! Here I restrict my discussion to classical physics domain.
    Potential Energy is defined for conservative forces or field. These conservative forces may be gravitational force, spring force ( obeying Hooke's Law), electrostatic forces (I believe all type of bonds explained in chemical reactions are essentially electromagnetic forces. Also inter atomic and inter molecular forces are the same).

    Following law is always applicable (classical Physics):
    Under the action conservative forces ONLY, sum of "kinetic energy and potential energy" of the system is always constant. Now it is your prerogative that you call it (the sum of Kinetic & Potential energy) what.
     
  15. Jun 20, 2012 #14

    PhanthomJay

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    that is the term used.
    I don't know how organized it is, but yes, mechanical energy, when used in this context, is energy of motion, and thus a form of kinetic energy. Ahh, definitions, we need a wordsmith on board....
     
  16. Jun 20, 2012 #15
    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    OK so...

    What other forces are there apart from conservative forces then?
     
    Last edited by a moderator: Jun 22, 2012
  17. Jun 20, 2012 #16

    PhanthomJay

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    expletive deleted . You are not the wordsmith I was looking for.
    Non- conservative forces. Gravity and spring forces are conservative. Friction, applied, and other contact forces are non conservative.
     
  18. Jun 20, 2012 #17
    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    So your saying PJ that there are two different "mechanical energies" that people refer to?
     
  19. Jun 20, 2012 #18

    PhanthomJay

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    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    There are two distinctions to which I refer. I can't speak for all people.
    Suppose that a motorized pulley is used to move a crate up an incline. The mechanical energy (definition 2) of the motor/pulley causes work to be done on the system which in turn increases the mechanical energy (definition 1) of the system. Well, what do you think, people, and what do you think, I-c?
     
  20. Jun 20, 2012 #19
    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    So are you saying here that because it is used out of context it is used to mean something completely different, so therefore mechanical energy has two meanings?
     
  21. Jun 20, 2012 #20

    PhanthomJay

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    Re: What exaclty is Mechanical Energy? Or more specificaly potential energy (the subs

    When i think of Chemical energy, I think of mixing chemicals together; when i think of Electrical energy, I think of powerlines; when i think of Nuclear energy, it's the bomb; when i think of Mechanical energy, I think of engines and machines. Each of these types of energy, and others I have not listed, are capable of producing changes to the kinetic and potential energies of a system, that is, changes to the mechanical energy of a system.
     
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