Fluids mechanics is also gas mechanics?

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    Fluids Gas Mechanics
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Discussion Overview

The discussion revolves around the classification of fluids in fluid mechanics, specifically whether gases should be considered part of fluid mechanics or if they warrant a separate classification as "gas mechanics." Participants explore definitions and implications of fluid mechanics, gas dynamics, and the nature of different states of matter.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants argue that gases are included in fluid mechanics because they are defined as fluids, which encompass liquids, gases, and plasmas.
  • Others contend that gases should not be classified as fluids in the same way as liquids, citing differences in behavior and definitions.
  • A participant mentions that there is a branch of fluid mechanics called "gas dynamics," which addresses the flow of gases under certain conditions.
  • Some participants express confusion over the definitions of fluids and states of matter, suggesting that the traditional classification of solids, liquids, and gases is inadequate.
  • There is a discussion about the viscosity of fluids and how it relates to their behavior in different contexts, such as in pipes.
  • One participant emphasizes the importance of accuracy in definitions and expresses concern over the implications of misclassifying gases.
  • Another participant highlights that both liquids and gases are considered fluids, with the distinction that liquids are generally incompressible while gases are compressible.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether gases should be classified under fluid mechanics or as a separate category. Multiple competing views remain regarding the definitions and classifications of fluids and states of matter.

Contextual Notes

Some participants reference definitions from chemistry and physics, indicating that there may be differing interpretations of what constitutes a fluid. The discussion also touches on the evolving nature of scientific classifications and the complexity of fluid behavior.

  • #31


It is not fashionable to teach basic mechanics quantities these days but here are some that are applicable to this hydraulic lift and other purely mechanical things like levers and pulleys.

{\rm{VelocityRatio = VR = }}\frac{{{\rm{distance}}\,{\rm{moved}}\,{\rm{byload}}}}{{{\rm{distance}}\,{\rm{moved}}\,{\rm{byeffort}}}}

{\rm{MechanicalAdvantge = MA = }}\frac{{{\rm{load}}}}{{\,{\rm{effort}}}}

{\rm{Efficiency = }}\frac{{{\rm{MA}}}}{{{\rm{VR}}}}

and finally what is really the law of conservation of energy

{\rm{load*distance}}\,{\rm{moved}}\,{\rm{by load = effort*distance}}\,{\rm{moved}}\,{\rm{by}}\,{\rm{effort}}

Which you can see equals MA * VR
 
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  • #32


Similarly, it can sometimes be assumed that the viscosity of the fluid is zero (the fluid is inviscid). Gases can often be assumed to be inviscid. If a fluid is viscous, and its flow contained in some way (e.g. in a pipe), then the flow at the boundary must have zero velocity

This is because the fluid sticks to the walls, right?

Perhaps a bit late, but I'd like to answer this question anyway.

I'll stick my neck out and say: yes, it is because the fluid sticks to the walls.
Or rather, the friction between the fluid and the wall makes it stand still where it makes contact with the wall (in modelling).
 

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