# Fluid-dynamics Definition and 4 Discussions

In physics 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 dynamics offers a systematic structure—which underlies these practical disciplines—that embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves the calculation of various properties of the fluid, such as flow velocity, pressure, density, and temperature, as functions of space and time.
Before the twentieth century, hydrodynamics was synonymous with fluid dynamics. This is still reflected in names of some fluid dynamics topics, like magnetohydrodynamics and hydrodynamic stability, both of which can also be applied to gases.

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1. ### HVAC Redirecting airflow

I want to change the direction of airflow from a fan. The fan is covering a window so as to bring fresh air into the workspace, exhausting warmer air through open windows throughout the workspace. It would help cool those in the immediate area of the fan if it were blowing 90 degrees to the...
2. ### How does a Western free reed work? (musical instruments)

In this post, I will describe, as best I have been able to determine, how a Western free reed works. As it is unlikely I will run into a physicist here who specializes in reeds, I will just ask people to speculate on the behavior of a reed given what you know about fluid dynamics or the...
3. ### I General guidelines on the physics of flows at junctions?

Let's start with a configuration in which one tube, A, splits into two, B and C. We can write the relationship $$A_A v_A = A_B v_B + A_C v_C$$ When I first saw this formula (which was very recently), I wanted to solve for ##v_B## and ##v_C## given all other values. I can't of course. There are...
4. ### Clarification on key concepts of string theory

I've been tasked with giving a presentation on any subject i like to my undergraduate physics class. Inspired by a recent lecture i attended by David Tong i have chosen to do a quick (10 minute) overview of the current state of theories beyond the standard model, obviously aimed at being...