Lecture

Life at Low Reynolds Number: Flagella Hydrodynamics and Blood Flow

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In course

BIO-244: Physics of the cell

Living organisms evolve in a physical world: their cells respond to mechanics, electricity and light. In this course, we will describe the behavior and function of cells using physical principles. ...

Description

This lecture delves into the hydrodynamics of flagella, modeling them as chains of small rods to understand how they propel cells forward. It explores the consequences of low Reynolds number flows and the drag forces involved in propulsion. Additionally, a simple model for blood flow in vessels is presented, considering factors like pressure difference and viscosity. The lecture also covers the concept of hydrodynamic resistance and how vessel dimensions affect the flow rate to maintain oxygen flux to organs.

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Instructor

Alexandre Louis André Persat

Expertise bacterial biophysics and bioengineeringmicrofluidicscellular biomechanics Teaching & PhD PhD Students Jann Lukas Ledergerber, Dea Mariette Müller, Marin Paul Geoffroy Marie Ollagnon, Han-Yi Huang, Alice Pellegrino, Shiro Otaki, Chia-Ni Tsai, Po-Long Hsiao Past EPFL PhD Students Lorenzo Anton-Louis Talà, Xavier Pierrat, Tamara Rossy, Alice Cont, Jeremy Wong, Sourabh Monnappa Kuppanda Jafri, Tania Distler Past EPFL PhD Students as codirector Gabriele Gambardella Courses Fluid mechanics (for SV)

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Physics

Mechanics: Fluid mechanics

Related concepts (29)

Fluid dynamics

In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and modelling fission weapon detonation.

Fluid mechanics

Fluid mechanics is the branch of physics concerned with the mechanics of fluids (liquids, gases, and plasmas) and the forces on them. It has applications in a wide range of disciplines, including mechanical, aerospace, civil, chemical, and biomedical engineering, as well as geophysics, oceanography, meteorology, astrophysics, and biology. It can be divided into fluid statics, the study of fluids at rest; and fluid dynamics, the study of the effect of forces on fluid motion.

Reynolds number

In fluid mechanics, the Reynolds number (Re) is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers, flows tend to be turbulent. The turbulence results from differences in the fluid's speed and direction, which may sometimes intersect or even move counter to the overall direction of the flow (eddy currents).

Drag (physics)

In fluid dynamics, drag (sometimes called fluid resistance) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or between a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, the drag force depends on velocity. Drag force is proportional to the velocity for low-speed flow and the squared velocity for high speed flow, where the distinction between low and high speed is measured by the Reynolds number.

Viscosity

The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity is defined scientifically as a force multiplied by a time divided by an area. Thus its SI units are newton-seconds per square metre, or pascal-seconds. Viscosity quantifies the internal frictional force between adjacent layers of fluid that are in relative motion.

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