Understanding Shear Modulus: How It Defines Fluid Properties

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Discussion Overview

The discussion revolves around the properties of fluids as defined by different moduli, particularly focusing on shear modulus and bulk modulus. Participants explore how these concepts relate to fluid behavior, especially in the context of compressibility and flow characteristics.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions which modulus defines a property of fluids, suggesting shear modulus as the answer.
  • Another participant argues that bulk modulus is more appropriate as it describes compressibility.
  • A later reply reiterates the preference for bulk modulus, indicating that their answer was not accepted in an academic context.
  • Some participants express confusion over the relationship between shear modulus and fluid flow, questioning how elasticity relates to fluid behavior.
  • One participant clarifies that fluids have zero shear modulus, allowing flow to occur under small shear stress, and acknowledges the vagueness of the original question while noting that bulk compressibility also characterizes fluids.
  • Another participant suggests that viscosity might be a more relevant property to consider when discussing fluid flow.

Areas of Agreement / Disagreement

Participants do not reach a consensus on which modulus is most relevant to defining fluid properties. There are competing views regarding the significance of shear modulus versus bulk modulus, and confusion persists about the relationship between these concepts and fluid flow.

Contextual Notes

The discussion highlights limitations in the original question's clarity and the assumptions regarding the definitions of shear and bulk moduli in the context of fluid mechanics.

Sudarsan
Which modulus define a property of fluids??

The above mentioned question was asked in my college internals. The answer they suggested was sheer modulus.
Any explanations??
 
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I would have been more inclined to say the bulk modulus that describes compressibility.
 
Dr.D said:
I would have been more inclined to say the bulk modulus that describes compressibility.
That was my answer, but they didn't accept it..
 
Oh, well, what can I say?
 
Dr.D said:
Oh, well, what can I say?
They said flow of fluids related to sheer modulus. I can't understand even a single bit of that, I don't know how flow of fluids can be compared with Elasticity
 
Fluids have zero shear modulus, so fluid flow can be driven by an arbitrarily small shear stress. In this way, the shear modulus (or lack thereof) does define fluids, and the flow of fluids is indeed "related" to the shear modulus. But the question is vague. The bulk compressibility also characterizes the mechanical response of fluids, of course.

An analogous question might be: What electrical material property defines a superconductor? Answer: The conductivity (infinite) or resistivity (zero).
 
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Sudarsan said:
They said flow of fluids related to sheer modulus. I can't understand even a single bit of that, I don't know how flow of fluids can be compared with Elasticity
It's a stupid question, but I would have answered viscosity (which describes the shear-stress/shear-rate behavior of fluids.
 
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