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Is a gravitational circuit possible?

  1. Nov 20, 2011 #1
    Is it possible to make mass elements flow by establishing a gravitational potential difference between 2 points in the circuit, like in an electrical circuit?

    In an electrical circuit, what makes the electrons flow is the fact they they repel each other right? The masses attract each other, so does that make a gravitational circuit impossible?
     
  2. jcsd
  3. Nov 20, 2011 #2

    D H

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    There's no such thing as negative mass. Think about that for a second.
     
  4. Nov 20, 2011 #3

    sophiecentaur

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    The nearest practical thing to what you are talking about would be an elevator carrying masses up to the top, giving them potential energy (the battery) and the masses dropping down a friction slope, arranged so that they arrive at the bottom with near zero velocity. The slope gets warm.(the resistor)
    That's a gravitational energy circuit.
     
  5. Nov 21, 2011 #4
    Fluid networks are like this:

    Pump = voltage source
    Orifice = resistor
    Long horizontal pipe = inductor+resistor in series
    Tank = capacitor

    Inductor and Resistor are nonlinear elements.

    Mechanical systems are like circuits too:

    Mass = inductor
    Spring = capacitor
    Damper = resistor
    Force = voltage source

    these are a lot more linear.
     
  6. Nov 22, 2011 #5
    That would be a river.
     
  7. Nov 22, 2011 #6

    sophiecentaur

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    What is non-linear about an Inductor or Resistor (assuming they are operating within their design parameters) any more than a Spring (which will have end stops) or a Damper (which can overheat just like a resistor)?
     
  8. Nov 22, 2011 #7

    FlexGunship

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    He meant that inductors and capacitors are not linear elements. This is because they require a dt variable to properly describe their operations. That is to say their current operation does not depend solely on the current conditions but rather on the previous state AND the current state.

    If you know instantaneous voltage across an ideal resistor you know the instantaneous current through it. This is untrue of ideal inductors and ideal capacitors during any transient.
     
  9. Nov 22, 2011 #8

    sophiecentaur

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    That's not what linearity means.
     
  10. Nov 22, 2011 #9

    FlexGunship

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    Strictly speaking you're correct because caps and inductors can only phase shift or attenuate signals. I believe the literal definition of a "linear circuit" (from my college days) is any circuit that doesn't change the fundamental driving frequency at the output. But I think that idea is what he was trying to get at.
     
  11. Nov 22, 2011 #10
    Fluid inductor means a long pipe in which the fluid has some KE therefore energy stored into it which is a function of volumetric flow rate. Fluid dynamics is nonlinear in general, especially in a long pipe where the flow is nonuniform with length.
    Same thing with fluid resistor, which is an orifice. The pressure drop across an orifice is highly nonlinear with volumetric flow rate, if you recall from fluid dynamics. This is hard to see intuitively either.

    Mass-spring-damper systems are much more linear in general. We had some set up in the lab for system dynamics class, and the data that came out is very close to what you predicted from solving the linear systems of ODEs.
     
  12. Nov 23, 2011 #11

    sophiecentaur

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    But when someone introduces a new idea / analogy into a thread in an attempt to explain things, the terms should be as strictly correct as possible, surely. There are 'minds' reading these gems of wisdom and drawing all sorts of conclusions. It doesn't help them if we use imprecise terms. A capacitor can distort a signal but such reactive elements produce Linear Distortion.

    I think your definition is fair enough - at least it gives a good example of linearity
     
  13. Nov 23, 2011 #12

    FlexGunship

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    Well, if you recall, the original comparison was to fluid dynamics where the term "linear" has a different meaning (i.e. time dependent), so for the comparison of an inductor to an arbitrarily long horizontal flow carrier of finite-diameter calling an inductor non-linear is useful only for comparison purposes. It might have been more helpful in my previous post to put the phrase "non-linear" in quotes.
     
  14. Nov 23, 2011 #13

    sophiecentaur

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    This again gets me onto my hobbyhorse about avoiding analogies wherever possible. It's full of pitfalls like this one.

    btw, I thought that "non-linear" was a general word to describe a relationship that involved terms with higher order than one or a situation where superposition operated. Though I have heard the term 'non-linear narrative' used to describe stories in which the action is presented out of order. I thought that was just sloppy Non-Scientists at work.
     
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