How can a non-flowing fluid have kinetic energy?

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Discussion Overview

The discussion centers around the concept of kinetic energy in non-flowing fluids, exploring how such fluids can possess kinetic energy despite not being in motion as a whole. Participants also examine the distinctions between different types of energy associated with fluids, including internal energy, potential energy, and flow energy.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that a non-flowing fluid can have kinetic energy due to the motion of its molecules, even if the fluid itself is not flowing.
  • There is a distinction made between internal kinetic energy, which refers to the motion of particles within the fluid, and the more common understanding of kinetic energy as the motion of the fluid as a whole.
  • One participant references the Bernoulli equation to illustrate the relationship between pressure energy, kinetic energy, and gravitational potential energy in an ideal fluid, questioning the inclusion of additional energy terms.
  • Another participant emphasizes the need to understand internal energy as a concept that encompasses both kinetic and potential energy at the microscopic level.
  • Some participants express uncertainty regarding the classification of flow energy and its relationship to kinetic energy.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definitions and relationships between different types of energy in fluids. Multiple competing views remain regarding the nature of kinetic energy in non-flowing fluids and the interpretation of energy terms in fluid dynamics.

Contextual Notes

Limitations include potential misunderstandings of energy definitions, the dependence on specific interpretations of fluid dynamics equations, and unresolved distinctions between various energy types.

eurekameh
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So a non-flowing fluid has energy that consists of internal energy, potential energy, and kinetic energy. If it is "non-flowing," how is this possible?

A flowing fluid has energy that consists of internal energy, potential energy, kinetic energy, and flow energy Pv. My other question is, shouldn't the flow energy be a part of its kinetic energy as well? Why are they different?
 
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Is this a homework question?
 
Note that in this case, potential energy is gravitational potential energy.

Bernoulli equation with gravitational term, for an ideal fluid with no external forces other than gravity:

pressure + 1/2 ρ v2 + ρ g h = total_energy / unit_volume

If you multiply this by some amount of volume you get energies:

(pressure x volume) + 1/2 m v2 + m g h = total_energy

pressure_energy + kinetic_energy + gravitational_potential_energy = total_energy

I'm not sure where you got the additional term from.
 
Make sure you understand that Internal Energy is not some kind of energy; instead it is a concept that includes kinetic and potential energy internal to the body, substance.

Also, make sure you understand the difference between Internal Kinetic Energy and Kinetic Energy in its more common sense.

Internal kinetic energy refers to the motion of the particles in the object, substance.

Regular kinetic energy, the more common concept as understood by most everybody, refers to the kinetic energy of the body as a whole due to its motion, translation.
 
The molecules of the fluid are moving, but the fluid doesn't necessarily have to flow.
 
Put the liquid in a sealed container wait for it to stop moving from your lifting it and drop it from a height.
 
rcgldr said:
Note that in this case, potential energy is gravitational potential energy.

Bernoulli equation with gravitational term, for an ideal fluid with no external forces other than gravity:

pressure + 1/2 ρ v2 + ρ g h = total_energy / unit_volume

If you multiply this by some amount of volume you get energies:

(pressure x volume) + 1/2 m v2 + m g h = total_energy

pressure_energy + kinetic_energy + gravitational_potential_energy = total_energy

I'm not sure where you got the additional term from.


You mean the internal energy term? Here's the equation from my textbook: http://imageshack.us/photo/my-images/850/unledkzh.png/
I can kinda see where everyone's coming from with the internal kinetic energy. But I would guess that would be a part of its total internal energy, which is already a part of the equation.
 

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