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**Isaac Newton's Philosophiae Naturalis Principia Mathematica**

The concept of viscosity is first introduced in Sir Isaac Newton’s *Philosophiae Naturalis Principia Mathematica*. Along with Newton’s primary discussion of natural philosophy and the theory of gravity, he reaches into the realm of fluid mechanics to develop the first mathematical description of viscosity as shear stress divided by the velocity gradient of a flow.

"Principia Philosophiae Naturalis Principia Mathematica, Title page" by CRC, University of Edinburgh is licensed under CC BY-NC-SA 2.0

- The Mathematical Principles of Natural PhilosophyEnglish translation of Philosophiae Naturalis Principia Mathematica

**Daniel Bernoulli's Hydrodynamica**

In Daniel Bernoulli’s *Hydrodynamica *describing--as the name suggests--the mechanics of moving water, he considers the basic properties of fluid flow. The central product of this work is the foundational Bernoulli equation relating pressure, velocity, density, and altitude properties of a flow.

Cover designer: Unknown author; Book author: Creator:Danielis Bernoulli; File edited by 青子守歌, Public domain, via Wikimedia Commons

- Hydrodynamica bookImages of entire book in original Latin

**Osborne Reynolds "An experimental investigation of the circumstances..."**

In Osborne Reynolds’ paper, "An experimental investigation of the circumstances which determine whether the motion of water in parallel channels shall be direct or sinuous and of the law of resistance in parallel channels", he introduces a mathematical value that can be calculated to distinguish laminar and turbulent flow. This “Reynolds number”, as it is now called, is a widely used criterion in modeling fluid flow.

John Collier, Public domain, via Wikimedia Commons

**Lewis Moody’s “Friction Factors for Pipe Flow” **

Lewis Moody’s Friction Factors for Pipe Flow is held as a key paper within the topic of theoretical hydrodynamics. This is not due to any new or groundbreaking information, but from the embodiment of accepted conclusions in convenient charts for engineering use. The most famous of these is deemed the “Moody chart” relating Reynold's numbers and relative roughness values to friction factors.

"File:Moody EN.svg" by Original diagram: S Beck and R Collins, University of Sheffield (Donebythesecondlaw at English Wikipedia) Conversion to SVG: Marc.derumaux is licensed under CC BY-SA 4.0

**Ludwig Prandtl’s “On the motion of fluids with very little friction”**

Ludwig Prandtl’s paper, "On the motion of fluids with very little friction", revolutionized the field of fluid mechanics in its mere eight pages through the first description of the boundary-layer concept in fluid flow. While theorizing that frictional effects were experienced solely in this thin region near the surface of a flow, he additionally proposed the no-slip condition of flow at a surface.

DLR, CC-BY 3.0, CC BY 3.0 DE <https://creativecommons.org/licenses/by/3.0/de/deed.en>, via Wikimedia Commons

**Ira H. Abbott’s “The drag of two streamline bodies as affected by protuberances and appendages”**

Ira H. Abbots N.A.C.A. Report 451 on “The drag of two streamline bodies as affected by protuberances and appendages” provides experimental data on the increase in drag caused by appendages of various size and location attached onto a streamlined body. The qualities (size, geometry, location) of these appendages are assessed regarding their increase in drag coefficient.