Measure visocity of water by poises

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Discussion Overview

The discussion centers on the measurement of the viscosity of water using the unit of poise, exploring its relationship with other physical quantities and the conceptual understanding of viscosity itself. The scope includes theoretical explanations, unit conversions, and conceptual clarifications regarding viscosity in fluids.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants mention that viscosity is commonly measured in centipoise, providing conversions to other units such as Pa·sec and Lbf·sec/ft².
  • There is a question about the interpretation of Pa·sec, with one participant suggesting it relates to atmospheric pressure over time, prompting further clarification on the definition of viscosity.
  • One participant defines viscosity as resistance to flow and elaborates that it measures a fluid's ability to resist shear stress, cautioning against misinterpretation of the units involved.
  • Another participant references Wikipedia to explain viscosity as a measure of a fluid's internal resistance to flow, noting that solids can exhibit viscosity under certain conditions and clarifying the distinction between kinematic and dynamic viscosity.

Areas of Agreement / Disagreement

Participants express varying interpretations of viscosity and its measurement, with no consensus reached on the best way to explain the concept to a layperson. There are competing views on the relationship between viscosity and pressure, as well as the appropriate units to use.

Contextual Notes

Limitations include potential misunderstandings regarding the nature of shear stress versus atmospheric pressure, as well as the distinction between kinematic and dynamic viscosity, which remains unresolved in the discussion.

MathematicalPhysicist
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i read that you measure visocity of water by poises (sounds like poison :rolleyes: ), how does it equate with the quantities?
i.e, like [N]=[kg*m^2/sec]
 
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For most applications, the standard is in centipoise.

1 cp = .001 Pa*sec or 1.45 x10^-7 Lbf*sec/ft^2 for us non SI'ers.

BTW...a Newton is [tex]\frac{kg*m}{sec^2}[/tex]
 
Pa*sec is pascal times seconds, right?
so visocity of liquids is actually the atmospheric presure against time, or in other words how do you explain to a layperson what visocity of liquids is?
 
In the most basic sense: Viscosity = resistance to flow. If you want to go a bit farther, viscosity is a measure of the ability of a fluid to resist shear stress.

You have to be careful in interpreting the units for viscosity. The pressure is not atmospheric pressure. It is shear stress. The mathematical relation for viscosity is:

[tex]\tau = \mu \frac{du}{dy}[/tex]

Where:
[tex]\tau[/tex] = shear stress
[tex]\mu[/tex] = viscosity
[tex]\frac{du}{dy}[/tex] = velocity distribution
 
http://en.wikipedia.org/wiki/Viscosity
Viscosity is a measure of the resistance of a fluid to deformation under shear stress.
Wikipedia

Viscosity is commonly perceived as "thickness", or resistance to pouring, however it really describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Adapted from Wikipedia.

Solids exhibit viscosity when subject to very high compressive or tensile stresses, e.g. extrusion or other forms of cold or hot working.

The pressure is not necessarily atmospheric pressure, but applied pressure, and this more a case that the term is in units of pressure. This expression refers to kinematic viscosity [itex]\nu[/itex] vs dynamic viscosity [itex]\mu[/itex], which have the following relationship

[itex]\nu[/itex] = [itex]\mu[/itex]/[itex]\rho[/itex]
 

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