# The Motion of a Fluid Affects Many Different Factors

Mastering Fluid Dynamics is the study of liquid or gas movement, and it's a subject that physicists take seriously. The motion of a fluid affects many different factors, so understanding the concepts that are relevant to this field is crucial for success in this discipline. Among the most fundamental of these concepts is fluid viscosity.

Viscosity is the internal frictional resistance that a fluid has to shear stress. In other words, it is the force required to shear a sheet of paper, but at a much lower magnitude than if you were to push on it with your finger.

All liquids have this natural internal friction, which physicists quantify using the term dynamic viscosity. It is important to understand viscosity, because it relates directly to the flow of layers with different velocities within a fluid. This is a basic principle that physicists have dubbed Bernoulli's law, named after Daniel Bernoulli in 1738.

The dynamic viscosity of a liquid depends on the temperature of the fluid and the speed of its flow. The higher the velocity, the greater the dynamic viscosity. However, this is also why fluids with higher viscosities are able to withstand more pressure than liquids with lower viscosities.

Dynamic viscosity quantifies a fluid's resistance to deformation under shear stress, which is another way of saying how gooey or sticky it feels. This is an essential factor when it comes to predicting and controlling the behavior of fluids in many practical applications, such as manufacturing pharmaceutical syrups and paint.

In order to determine the dynamic viscosity of a fluid, physicists use a tool called a rheometer. This device measures the shear stress required to break down a sample of the fluid, taking into account its viscosity and temperature. This information is then used to model and predict the behavior of the fluid in its surroundings.

Understanding how the dynamic viscosity of a substance is affected by its temperature opens up a reservoir of knowledge that boosts your ability to manage fluid behaviors in a variety of settings. This includes everything from managing pipe flows in chemical engineering processes to designing a drug delivery system for a hospital.

The unit of measurement for dynamic viscosity is the centipoise (abbreviated cP), which represents 1/100 of a poise. One poise equals 10 cP, so 1 cP is equivalent to 1000 poise-seconds (Pa s). This unit of measure is more common than the SI unit pascal second, which is often abbreviated as Pa s. The SI unit for absolute viscosity is the stoke, which is named after the Irish mathematician George Gabriel Stokes who helped develop the Navier-Stokes equation. This is a common unit of measurement in the petroleum industry and is equivalent to 0.01 poise. However, the stoke is rarely used outside of these contexts, as it is not as familiar to non-physicists. A stoke is also equal to the density of a fluid in g/cm3. The tenth part of a poise-second is often left unwritten because it is not considered important in most applications.