Poiseuille's Law
Poiseuille's Law - Related Videos
01:10
Poiseuille's Law and Reynolds Number
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2025
Any fluid in a horizontal tube can flow due to pressure differences—fluid flows from high to low pressure. The flow rate (Q) is the ratio of pressure difference and resistance through a horizontal tube. The greater the pressure difference, the higher the flow rate. The flow resistance is expressed as: When combined with the flow rate (Q), this relation gives Poiseuille's law for the laminar flow of an incompressible fluid in a tube. All factors that affect the flow rate, except pressure, are...
02:53
Beer's Law - Concepts
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2020
Absorbance and Fluorescence When light hits a substance, it is either absorbed, transmitted, or reflected. Typically, a substance interacts with a range of wavelengths of light, each one interacting with the molecules or atoms differently. A substance may absorb a specific range of wavelengths, reflect another range of wavelengths, and transmit the other wavelengths of light. When a molecule absorbs light, the energy is used in four different ways: (1) translation, which causes the molecule to...
02:38
Third Law of Thermodynamics
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2020
A pure, perfectly crystalline solid possessing no kinetic energy (that is, at a temperature of absolute zero, 0 K) may be described by a single microstate, as its purity, perfect crystallinity,and complete lack of motion means there is but one possible location for each identical atom or molecule comprising the crystal (W = 1). According to the Boltzmann equation, the entropy of this system is zero. This limiting condition for a system’s entropy represents the third law of thermodynamics: the...
02:49
Second Law of Thermodynamics
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2020
In the quest to identify a property that may reliably predict the spontaneity of a process, a promising candidate has been identified: entropy. Processes that involve an increase in entropy of the system (ΔS > 0) are very often spontaneous; however, examples to the contrary are plentiful. By expanding consideration of entropy changes to include the surroundings, a significant conclusion regarding the relation between this property and spontaneity may be reached. In thermodynamic models, the...
10:12
Newton's Laws of Motion
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2023
Source: Andrew Duffy, PhD, Department of Physics, Boston University, Boston, MA This experiment examines at various situations involving two interacting objects. First, the experiment examines the forces that two objects apply to one another while they collide. The objects are wheeled carts that have variable masses. The purpose of this experiment is to discover when the force the first cart exerts on the other is the same magnitude as the force the second cart exerts back on the first, as well...
FAQs
The radius appears to the fourth power, so small changes in a tube’s internal radius can produce much larger changes in volumetric flow than comparable changes in other variables. Increasing the radius therefore sharply lowers flow resistance, whereas narrowing the tube sharply restricts transport. This sensitivity is especially important when analyzing capillary movement or designing microfluidic channels.
Poiseuille's law is appropriate when fluid motion is steady and laminar, the fluid is incompressible, and the fluid behaves as a Newtonian material. These conditions define the situation represented by the relationship among pressure difference, viscosity, tube dimensions, and flow rate. Checking them helps researchers decide whether calculated transport values are meaningful for a chemical system.
A larger pressure difference produces a greater volumetric flow, while a longer tube produces a smaller one. Pressure difference supplies the driving force for transport, whereas tube length contributes to flow resistance. This distinction allows experimentalists to adjust driving conditions or tubing dimensions independently when seeking a desired flow rate in laboratory transport systems.
A calculation requires the pressure difference across the tube, the tube radius, the tube length, and the fluid viscosity. These quantities are combined according to their different effects on transport, with radius receiving particularly strong weight because of its fourth-power dependence. The resulting estimate can guide tubing selection or predict delivery rates in a controlled setup.
Viscosity can be determined by observing flow through a tube whose dimensions are known while controlling or measuring the pressure difference. The measured flow response is then interpreted with Poiseuille's law to obtain the fluid property responsible for resistance to transport. In chemistry, this provides a way to characterize fluids using laboratory tubing rather than relying only on composition.
The relationship supports analysis of capillary transport, flow resistance in laboratory tubing, and controlled movement through microfluidic devices. It also helps researchers design systems for chemical delivery and analysis by connecting geometry and fluid properties with expected flow. These applications make the law useful for planning reproducible transport conditions and interpreting flow-related experimental results.