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Thevenin/Mechanical analogy

  1. Sep 5, 2005 #1
    My lecturer mentioned something about how you can represent Thevenin equivalent circuits with forces etc. As a mech eng student, this would be easier to understand than stupid resistors and voltages. :)

    Does anyone know what Im on about? I cant think of how you could do this, but then again, I dont really understand Thevenin all too well.

  2. jcsd
  3. Sep 6, 2005 #2


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    In making an electrical/mechanical analogy, you can replace currents by forces, voltages by velocities, resistances by viscous friction (the friction force is proportional to speed), capacitances by masses and inductances by the inverses of spring constants.
    Does it help?
  4. Sep 6, 2005 #3
    A) A pump which holds a constant pressure at the head and can deliver infinite
    flow is connected to a flowmeter via a section of finite diameter pipe.

    B) A second pump which maintains a constant flow rate and can develop any
    pressure at the head is connected to itself with another short pipe section.
    A pressure gauge measures the pressure at across this pipe.

    For any type of pump and pipe section in situation A, you can find another
    pipe and pump of type B that will have an identical pressure and flow
    rate for any type of a second branch pipe you may connect to either
    A or B. You won't know from measuring the flow and pressure at the service
    pipe whether you are geting your fluid from a type A or type B system.
  5. Sep 11, 2005 #4
    Hmm, Im still a bit confused, but I kinda get it. Thanks guys.
  6. Sep 30, 2005 #5
    What exactly are you having trouble with in understanding Thevenin equivalent circuits?
  7. Sep 30, 2005 #6

    This mechanical analogy may not be physically correct, but the idea is the same.

    Suppose you pick any I-beam in a skyscraper, and want to analyze all forces, shears and stresses that are acting on it. If you could reduce all that junk to a single force and shear you could model whats going to the I-beam.

    Similarly with resistors (I-Beam)

    Suppose you have a glob of interconnected resistors with voltage and current sources. If you pick any resistor in the circuit, you can model whats going on between the two nodes across you resistor with a single voltage source (thevenin) and another resistor (thevenin).

    If you then take your resistor that you picked and connect it to the thevenin voltage source and the thevenin resistor, it will give you the same effect if your resistor was connected to whole circuit.
    Last edited: Sep 30, 2005
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