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Related Concept Videos

Viscosity01:17

Viscosity

7.1K
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.
The SI unit of viscosity is...
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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

Newtonian Fluid: Problem Solving

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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.
A velocity gradient forms within the fluid when a Newtonian fluid is placed between two parallel plates, with...
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Stokes' Law01:20

Stokes' Law

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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.
The expression for the force on a solid spherical object in a fluid is called Stokes' law. Stokes' law is valid only...
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Laminar and Turbulent Flow01:07

Laminar and Turbulent Flow

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Fluid dynamics is the study of fluids in motion. Velocity vectors are often used to illustrate fluid motion in applications like meteorology. For example, wind—the fluid motion of air in the atmosphere—can be represented by vectors indicating the speed and direction of the wind at any given point on a map. Another method for representing fluid motion is a streamline. A streamline represents the path of a small volume of fluid as it flows. When the flow pattern changes with time, the...
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Surface Tension, Capillary Action, and Viscosity02:57

Surface Tension, Capillary Action, and Viscosity

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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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Updated: Jan 4, 2026

Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions
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Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions

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Active Particles in Viscosity Gradients.

Charu Datt1, Gwynn J Elfring1

  • 1Department of Mechanical Engineering and Institute of Applied Mathematics, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada.

Physical Review Letters
|November 9, 2019
PubMed
Summary
This summary is machine-generated.

Microswimmers exhibit viscotaxis in viscosity gradients, moving towards or away from areas with different fluid thickness. This behavior depends on their swimming style and can be used for particle control and sorting.

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Area of Science:

  • Physics
  • Fluid Dynamics
  • Biophysics

Background:

  • Microswimmers, such as bacteria or artificial micro-robots, operate in complex fluid environments.
  • Natural environments often feature spatial gradients in fluid viscosity, impacting microswimmer dynamics.

Purpose of the Study:

  • To theoretically investigate the dynamics of active particles in viscosity gradients.
  • To understand how viscosity gradients influence microswimmer behavior and explore potential applications.

Main Methods:

  • Utilizing the squirmer model to represent active microswimmers.
  • Developing theoretical results for particle dynamics in non-uniform viscosity fields.

Main Results:

  • Demonstrated that viscosity gradients induce viscotaxis in squirmers.
  • Showed that the effect of viscosity gradients is dependent on the microswimmer's specific swimming gait.
  • Identified that viscosity gradients can be leveraged for active particle manipulation.

Conclusions:

  • Viscosity gradients are a significant factor in microswimmer navigation and behavior.
  • Microswimmer swimming style dictates their response to viscosity gradients.
  • This phenomenon offers a method for controlling and sorting microswimmers based on their locomotion strategy.