# What is Fluid motion: Definition and 15 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. ### Hydrostatic pressure distribution despite fluid motion

Hello, in some exam questions I've looked at it is stated that the pressure distribution is hydrostatic, even though there is fluid motion. (In these cases the velocity has been constant over the section where the pressure is said to be hydrostatic). Is it really possible to assume that the...
2. ### Calculating CO2 expansion time and generated suction

I need help with figuring out how to devise an equation that I'm going to plug into an algorithm for my software. These are the components: CO2 cartridge pressure regulator output should be around 200 psi. Tank #1 has a volume of 800 mL, pressure is around 15 psi. There are no valves between...
3. ### Force Produced from Fluid Motion

Dear all, I have a question that has eluded explanation in fluid mechanics textbooks and even some of my colleagues. Suppose we have a general control volume. The application of linear momentum conservation will yield an equation of the form, \frac{\partial}{\partial t} \int_{V\llap{-}} \rho...
4. ### Fluid Flow Equations With Real Values

Hi, all I am working on a project that involves analyzing fluid flow behavior in oil & gas pipelines. I am interested in calculating and plotting the velocity profile, and also(pressure distribution, temp distribution) Having studies fluid mechanics last year I am aware of the EOS for fluid...
5. ### Lagrangian description of fluid motion

Homework Statement Find velocity, acceleration, stream function and vorticity. Prove that velocity is equal to the acceleration. Functions given: X_1(t,e_1,e_2)= (e^\lambda)^t[e_1cos\omega t+e_2sin(\omega t)] X_2(t,e_1,e_2)= (e^-\lambda)^t[-e_1sin\omega t+e_2cos(\omega t)] Homework Equations...
6. ### Verifying Stokes' Flow for Fluid Motion Around a Sphere

Homework Statement Let a spherical object move through a fluid in R3. For slow velocities, assume Stokes’ equations apply. Take the point of view that the object is stationary and the fluid streams by. The setup for the boundary value problem is as follows: given U = (U, 0, 0), U constant, find...
7. ### Modeling Deceleration of Object Towed in Water

So this is about a modelling project I'm doing. If you have an object that was being towed in water and the towing force is suddenly removed. There is a force F=1/2(density of fluid)(C constant)(A)V^2 that acts on the object. I am trying to find the distance X it will take for the object to...
8. ### Fluid Mechanics - Resistance to fluid motion using Chezy's formula

Homework Statement The quantity of water delivered through a buried pipe line that is 2 000 m long and has an inside diameter of 200 mm has over the years steadily decreased to 80 % of its original flow. This is due to encrustation inside the pipe. It was then decided to have the pipe...
9. ### Understanding bulk fluid motion under Lorentz force

I am trying to understand how the Lorentz force affects bulk fluid motion when I have an applied electric field (y-axis), applied magnetic field (x-axis) and bulk fluid velocity (z-axis), all orthogonal to each other. I understand that if the fluid was at rest, an electrostatic force would...
10. ### Derivations for Continuity equation of Fluid & Euler's Equation of Fluid Motion

Will anyone give me the derivations for continuty equation of fluid and euler's equation of fluid motion .
11. ### How to predict the volume of a tank of water at any time? (fluid motion)

We have a cylindrical tank of known dimensions. Attached at the bottom is a pipe perpendicular to the tank of known dimensions. We fill the tank with a liquid and let it drain out through the pipe. What formula will predict the volume of the tank at any time t? I believe the Hagen–Poiseuille...
12. ### Solving Smoke Ring Mysteries: Exploring Fluid Motion

Hi all, I'm trying to answer the following questions related to a project on smoke rings. We are in an introductory class, so this project is more for fun and just applying the little we have learned about point, rigid body, and fluid motion to something less understood like vortex rings...
13. ### Fluid motion in venturi flowmeter

Homework Statement The venturi flowmeter is used to measure the flow rate of water in a solar collector system. The flowmeter is inserted in a pipe with diameter 1.9cm; at the venturi of the flowmeter the diameter is reduced to 0.64cm. The manometer tube contains oil with density 0.82 times...
14. ### Calculate Pressure in Fluid Motion Pipe with Bernoulli's Principle

hi, I am just assumin this is the right place for bernoulli stuff pressure 1 and 2 are both static pressures, and the arrow shows fluid motion is it possible to calculate them directly from an equation? or is it simply P1 and P2? and also, since the diameter decreases for P2, the...
15. ### Torque in circular fluid motion

I'm reading a book (intro to, by Davidson) about MHD now, but found I'm a bit rusty on tensors and curvilinear coordinates. It is written that for a circular flow the azimuthal component of the NS equations in the steady state gives (with F some body force) \tau _{r \theta} r^2 =-\int _0 ^r...