Compressible vs. incompressible substance

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SUMMARY

In classical thermodynamics, gases and liquids are classified as compressible substances, while solids are generally treated as incompressible. The state principle, which states that two independent properties can define all other properties, applies primarily to gases and liquids. In fluid mechanics, liquids are often approximated as incompressible due to negligible density changes under pressure. However, all materials exhibit some level of compressibility, with the degree varying significantly across different phases.

PREREQUISITES
  • Understanding of classical thermodynamics principles
  • Familiarity with the state principle in thermodynamics
  • Basic knowledge of fluid mechanics concepts
  • Awareness of material properties related to compressibility
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  • Research the state principle in thermodynamics
  • Explore the compressibility of different materials in various phases
  • Study fluid mechanics assumptions regarding incompressible fluids
  • Investigate real-world applications of compressibility in engineering
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Students and professionals in physics, engineering, and materials science who seek to understand the compressibility of substances and its implications in thermodynamics and fluid mechanics.

gkiverm
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I'm confused about which phases are considered compressible and which are considered non-compressible.

In classical thermodynamics, gases and liquids are considered compressible. This is what the state principle (2 independent properties define all other properties) applies to gases and liquids. Am I correct in assuming solids are incompressible and thus the state principle doesn't apply to solids? Because we never study solids in my classical thermodynamics class.

In fluid mechanics, we often treat liquid as incompressible. For this reason, we usually assume the density of the fluid doesn't change as the pressure changes.

Can someone clear this up for me. Thanks!
 
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Essentially everything is compressible to some level when considering gases, liquids, and solids. The only questionis how compressible. In many cases volume will change very little with pressure and approximating with the material being incompressible is not a bad idea.
 
Its all relative. A black hole will compress anything (we think).
 

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