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What is work?

  1. Aug 31, 2016 #1

    Beanyboy

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    Could work be defined as: "The price we make electrons pay for redistributing themselves uniformly"? (Even though, we may have rigged the game initially, by configuring them unevenly)

    I'm trying to learn about electricity and toying with definitions that help. Incidentally, I do love: "The electron is the salmon of electricity swimming upstream in a ghostly river of conventional current".
     
  2. jcsd
  3. Aug 31, 2016 #2

    Mark44

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    The term "work" is already defined:
    $$W = \int \vec{F} \cdot \vec{ds}$$
    where ##\vec{F}## is force, and ds is an increment of distance an object is moved.

     
  4. Aug 31, 2016 #3

    Vanadium 50

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    I don't think this a good definition of "work". It's already defined, and it's not clear that your definition agrees quantitatively with the existing one.
     
  5. Aug 31, 2016 #4

    Beanyboy

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    Let me try that again.
    I'm assuming that electrons are predisposed to moving across an electric potential, i.e. there is a voltage. I want to describe to myself the movement of those electrons as they move. Can I say that we harness the energy they possess as they move? Can I say we use that energy to make things move, glow, heat up? Can I say, the movement of the electrons has benefited us?
     
  6. Aug 31, 2016 #5

    Beanyboy

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    How would you define work? Please try avoid using mathematical formulas as we'll only end up going round in circles. I appreciate your consideration and help.
     
  7. Aug 31, 2016 #6

    A.T.

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    Wrong forum.
     
  8. Aug 31, 2016 #7

    Beanyboy

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    Sorry and thanks for moving it.
     
  9. Aug 31, 2016 #8

    Mark44

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    The movement of electrons through a conductor is called an electric current., and is defined as the time rate of change of charge, another term that is well-defined.

    Of course we can harness this entergy, in the ways you have listed below and a lot more, such as in computers, radar, and on and on.
    I can't tell if this is a serious question...
     
  10. Aug 31, 2016 #9

    Mark44

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  11. Aug 31, 2016 #10

    Beanyboy

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    Maybe you overlooked the line in my original post, "I'm trying to learn about electricity". So, yes, this is a perfectly valid question if you're wading through the thickets of terminology as I am. I do appreciate your help. Thanks.
     
  12. Aug 31, 2016 #11

    Beanyboy

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  13. Aug 31, 2016 #12

    Mark44

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    No, I didn't overlook that line, but I thought it would be obvious to the most casual observer that we harness the energy of moving electrons. Since you are a teacher, as you stated in another thread, I assumed that you would have at least an inkling of how electricity works.
     
  14. Aug 31, 2016 #13

    ZapperZ

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    Because the water can be lifted up in 2 seconds, or 2 hours, and the work done, by definition, is the same. The power, which is time rate of work done, is different. But the work done is the same.

    You really ought to learn the physics first before attempting to make some sort of conceptual understanding of this. Otherwise, you're making up your own erroneous ideas as you go along. Is this what you want to do?

    Zz.
     
  15. Aug 31, 2016 #14

    Mark44

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    Not for work, but time is involved in the definition of power. In other words, the same amount work is done if you lift 50 gal. of water 25 feet, whether it takes you a minute or 8 hours.
     
  16. Aug 31, 2016 #15

    Beanyboy

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    Ah yes, Mark, I am a teacher. However, I am not a teacher of Math, or Physics, or Chemistry. I am a teacher of English language/literature and basic arithmetic.I'm currently studying, purely for pleasure, AP Physics and Chemistry, mainly using Khan Academy. Struggling a bit, but loving it. "Just keep swimming".
    Love the PF already. Bought a great book on logic yesterday as a result of another thread on PF. Thanks for your patience and understanding.
     
  17. Aug 31, 2016 #16

    Beanyboy

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    • Poster has been reminded to be civil in posts here on the PF.
    I'm really sorry to have upset you. You see, it's been a really busy morning here at CERN. Thanks for taking the time to share your brilliance. Now, if you'll excuse me, I have to get back to fixing the flux capacitor.
     
  18. Aug 31, 2016 #17

    Mark44

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    I'm sure you didn't upset Zapper, but you really should take his recommendation to heart. Without an understanding of the definitions of the basic terms, such as work and power, trying to come up with a conceptual understanding of things is an exercise in futility.

    In any case, we know you aren't working at CERN -- if you were, you wouldn't be asking the questions you're asking. And snide comments are not welcome here.

    I should add this: Before starting a thread like this one, "What is work," show us that you have done a bit of research, such as looking up the definition of this term.
     
  19. Aug 31, 2016 #18
    @Beanyboy
    You used this fiction line about CERN before, haven't you? :smile:
     
  20. Aug 31, 2016 #19

    Beanyboy

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    "You're making up your own erroneous ideas as you go along. Is this what you want to do"? Now, is that really helpful as a remark?
     
  21. Aug 31, 2016 #20
    It looks more like a question.
    But I am not an English teacher. :smile:
     
  22. Aug 31, 2016 #21

    Mark44

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    Yes, when a course correction is called for.
     
  23. Aug 31, 2016 #22

    Beanyboy

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    Oh, I'm sorry. I thought he was using it sarcastically. You know, like he was trying to belittle me. I'm hypersensitive. I've really got to up my meds!

    Hey, thanks man!
     
  24. Aug 31, 2016 #23
    It is the integral of a force over the distance. What this means is it tells you how much energy is being put into a system, regardless of time, which makes it useful to express a system as a state function such as energy. When you talk about a conservative force, it is the potential energy, which helps us explain why orbits work. In orbits and other oscillatory motions in classical mechanics governed by conservative forces, it is as if the potential energy and the kinetic energy (a measure of 'how fast you are' [squared times half the mass]) are playing ball, constantly moving energy back and forth between states, as energy is a state function. Again useful when you aren't worried about time.

    As for electronics and electrical engineering, we have a conservative force, however, the source does not have an infinite amount of energy, i.e. the battery drains out. The work generated by a battery is regarded as a potential, a bucket with a certain amount of water. It is more useful to use the electric fields, which can be thought of as odors, rather than the force.
    Protons: emit positive odors, hate positive odors, like negative odors.
    Electrons: emit negative odors, hate negative odors, like positive odors.
    The further away the particle is from a the source of an odor, it senses that said odor as less potent.
    If the particle likes the odor, it will move closer, if it hates it, it will move away.
    Also they can't smell themselves, so we are golden with those rules.

    So we need to use a different quantity, electric tension, the integral of the electric field over distance. This is not however a measure of energy, but this quantity is constant to every power source (in theory) and does not care whether you have 1 meter wire or 10 meters of the same wire, the tension is the same. With that we can conclude the electric field decreases if it is a longer wire, in a sense the longer wire has more resistance, how hard it is for the battery to generate a field with the given tension.
    The real method of proving resistance though involves more math and vector analysis, but at the end of the day V=IR, ohm's law, will pop in your notebook.

    We know resistance is how hard it is to generate a field, and know what is Voltage (electric tension), what is I? Well, within the real proof you will find that I is the current, how much charge is being transferred at a given time. I know you have requested no maths, but it is virtually impossible for me to base my explanations on anything but. Then again the language of physics IS math so please bare with me as I wave my hands with math that would surely make mathematicians scream at me.
    If we apply just a little calculus:
    F=qE
    ∫F⋅ds
    =∫qE⋅ds
    because our charge q is of a point charge, we can take it outside of the integral and thus:
    U=qV
    where U is energy, and V is the voltage
    but wait we have current not charge, and current is the change of charge over time:
    (d/dt)U=(d/dt)qV
    For the purposes of demonstration we shall assume constant voltage (DC) so V remains as is:
    dU/dt=V(dq/dt)
    Now we got Power, change of energy for a given time, we shall denote that as P.
    P=VI [from ohm's law: P=IV=I2R=V2/R]

    So now finally after all this math we can summarize:
    Each battery has a certain capacity, the amount of energy it holds, it is your bank account in circuits. When a circuit is connected, it will allow a current to flow, like a service company, however no service is free, it needs food, so it will require you to pay money, but unlike a service which will want money in regular intervals, the circuit will require you to apply power constantly. If you run out of energy, the circuit will stop giving you service.

    Physically, work is the difference between an extreme state to a state of equilibrium for non-conservative forces. Charges will happily move to where they want to be, state of equilibrium, but for that they lose energy. Although the electric force is conservative for the purposes of most circuits, you have some form of friction, which isn't conservative, which is why electrons don't flow forever in an oscillatory motion. In regard to the salmon analogy, they are not flowing upstream, they flow downstream, they just hit rocks on the way. A clumsy fish that is I should say.

    I should stress though, analogies are okay to get you started, but as you progress you need to treat the electric circuit as it is, an electric circuit. It'll help you understand the basics of ohm's law but once you start to look at RC circuits, semiconductor circuits, electro-mechanical machinery etc., you are getting into the realms of differential equations, and analogies will not solve you those equations, they can only get you as far as to express the circuit in terms of its components in a differential equation. At that point and on work is the amount you pay for the circuit to keep working. That is from an engineering point of view.
     
    Last edited: Aug 31, 2016
  25. Aug 31, 2016 #24

    Beanyboy

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    This really kind and considerate of you to take the time out to try to explain to me this tricky concept. I'm trying to learn how to "speak Physics". I appreciate the comment that that language of Physics is Math. I'm working on that too. Tell you what, I have to leave now. Later, I'll print this off and try my best to digest it. But once again, the fact that you've taken time out to explain to me is, well, what can I say, very generous of you indeed. Later.
     
  26. Aug 31, 2016 #25
    You are very welcome, hopefully it'll help you. :)
    I recommend however picking up books that can teach you some basic principles:
    For circuits, books that can teach you circuit analysis and provide practical examples and practices.
    For electrostatics and electrodynamics, you may want to start with Newtonian mechanics first and understand that before heading on to electrostatics and electrodynamics, things can get quite abstract and very mathematical there, where Newtonian mechanics is less so. Of course not to forget math itself. Best to get your feet wet first before heading into the ocean as always.
     
    Last edited: Aug 31, 2016
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