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Related Concept Videos

Viscosity of Fluid01:19

Viscosity of Fluid

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Viscosity measures the resistance a fluid offers to flow and deformation. It results from internal friction between layers of fluid moving relative to one another. Dynamic viscosity, denoted by the Greek letter mu (μ), quantifies the force needed to move one fluid layer over another. For Newtonian fluids like water and air, the relationship between the shearing stress and the rate of shearing strain is linear, meaning their viscosity remains constant regardless of the applied stress.
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Newtonian Fluid: Problem Solving01:18

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Newtonian fluids exhibit a constant viscosity, meaning their shear stress and shear strain rate are directly proportional. This property ensures a predictable and stable response to applied forces, maintaining a linear relationship between force and flow. Examples include water, air, and light oils, consistently demonstrating this proportional behavior regardless of external conditions.
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When water is poured into a glass, it falls freely and quickly, whereas if honey or maple syrup is poured over a pancake, it flows slowly and sticks to the surface of the container. This difference in the flow of different kinds of liquids arises due to the fluid friction between the liquid layers and the liquid and the surrounding material. This property of fluids is called fluid viscosity. In this example, water has a lower viscosity than honey and maple syrup.
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Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...
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Viscous forces, like friction, are intermolecular forces that resist the relative motion of molecules over each other. When a solid body moves through a liquid, viscous forces drag it in the opposite direction. The force's magnitude depends on the solid's shape and size, as well as its speed and the liquid's coefficient of viscosity, density and temperature.
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Dimensionless groups in fluid mechanics provide simplified ratios that help analyze fluid behavior without relying on specific units. The Reynolds number (Re), which represents the ratio of inertial to viscous forces, distinguishes between laminar and turbulent flows, making it essential in the design of pipelines and aerodynamic surfaces. The Froude number (Fr), the ratio of inertial to gravitational forces, is particularly useful in predicting wave formation and hydraulic jumps in...
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Minimal quantum viscosity from fundamental physical constants.

K Trachenko1, V V Brazhkin2

  • 1School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, UK.

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Researchers discovered a new fundamental lower limit for fluid viscosity, termed elementary viscosity. This viscosity is defined by fundamental physical constants and the proton-to-electron mass ratio, offering new insights into fluid dynamics.

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Area of Science:

  • Fluid Dynamics and Condensed Matter Physics

Background:

  • Fluid viscosity is highly system-dependent, spans many orders of magnitude, and is complexly related to molecular interactions and structure.
  • Existing first-principles theories struggle to accurately predict viscosity due to these complexities.

Purpose of the Study:

  • To identify a new fundamental quantity that sets the minimal kinematic viscosity of fluids.
  • To introduce and define a new property, "elementary" viscosity, with a lower bound determined by fundamental physical constants.

Main Methods:

  • Derivation of a new quantity representing the minimal kinematic viscosity based on electron and molecule masses.
  • Introduction of the "elementary" viscosity (ι) defined by fundamental physical constants, including the proton-to-electron mass ratio.
  • Comparison of the derived results with existing bounds in strongly interacting field theories.

Main Results:

  • A novel quantity is identified that establishes the minimal kinematic viscosity of fluids.
  • The "elementary" viscosity (ι) is introduced, with its lower bound determined by fundamental constants and the proton-to-electron mass ratio.
  • A connection is established between these findings and the Kovtun, Son, and Starinets bound in field theories.

Conclusions:

  • A universal lower bound for fluid viscosity, based on fundamental physical constants, has been established.
  • The concept of "elementary" viscosity provides a new theoretical framework for understanding viscosity limits across different systems.
  • The findings offer new perspectives on the behavior of matter at fundamental levels and in extreme conditions.