What is Fluids: Definition and 518 Discussions

In physics, a fluid is a liquid or gas or other material that continually deforms (flows) under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear force applied to them.
Liquids form a free surface (that is, a surface not created by the container) while gases do not.
Although the term "fluid" generally includes both the liquid and gas phases, its definition varies among branches. Definition of "solid" vary as well, and depending on field, some substances can be both "fluid" and "solid". Viscoelastic fluids like Silly Putty appear to behave similar to a solid when a sudden force is applied. Also substances with a very high viscosity such as pitch appear to behave like a solid (see pitch drop experiment). In particle physics, the concept is extended to include fluidic matters other than liquids or gases. "Fluid" in medicine and biology specifically means any liquid constituent of the body (body fluid), whereas "liquid" is not used in this sense. Sometimes liquids to be taken for fluid replacement, either by drinking or by injection, are also called "fluid" ("drink plenty of fluids"). In hydraulics, "fluid" is a term which refers to liquids of certain properties, and is a broader concept than "(hydraulic) oils".

View More On Wikipedia.org
Recent contents Top users
  1. A

    Understanding pressure in fluids

    Okay so I already asked a bit about this, but I think I'm going to need to post several questions on this to understand it, so here goes: I understand the definition of pressure, just not how it is applied to fluids. How is pressure in a fluid to be interpreted. Is it the force that the...
  2. S

    Continuum hypothesis of fluid mechanics (& relativistic fluids)

    Continuum approximation of fluid mechanics (& relativistic fluids) I have a few 'foundational' questions on fluid mechanics which I haven't been able to find quick answers to, any help would be appreciated. At the start of any course on fluids, one is told of the continuum hypothesis...
  3. X

    What is the density of the bird statue?

    Homework Statement An antique yellow statuette of a bird is suspended from a spring scale. The scale reads 11.81 N when the statuette is suspended in air, and it reads 11.19 N when the statuette is completely submerged in water. a. Find the volume of the statuette b. Is the bird made of gold...
  4. M

    Heat Equation for Compressible Fluids: Valid or Not?

    Hi everyone, I am wondering if the heat equation is valid for compressible fluids like air. This is assuming constant 100% humidity. If it is not then how close is the appoximation. The model assumes that heat moves through an array of air only by conduction. At the moment I use a...
  5. T

    Uncovering the Overshadowed Contributions of Newton to Fluid Mechanics

    Why is Newton's work on fluids rarely cited? And when cited it is not usually credited. Even If they called it a 'Newtonian fluid" they don't bother telling everything Newton did.
  6. G

    Fluids Homework: Density & Velocity Fields with Constants R, L, C, K

    Homework Statement Let R, L, C, K be suitable dimensional constants. In a certain motion of a fluid, the mass density function ρ is given in the Eulerian description by ρ = R*(x1^2+L^2). Is the velocity field v1 = C/(R*(x1^2+L^2)) e1 a possible velocity field? Is v2 = K*exp(-x1/L)...
  7. R

    Question: Does Increasing Fluid Speed Increase Temperature?

    Hi, I have a question about fluid temperature. I have a vague understanding that a fluid's temperature is its average kinetic energy. So, a hotter fluid has faster moving molecules on average. What I'm wondering is, if you force water out of a faucet harder to make the water come out...
  8. B

    Fluids Mechanics, finding height in the piezometric tube

    A large open tank, shown below, contains water at a height H. The water is allowed to flow out through a pipe whose cross-sectional area is A. The pipe has a nozzle at the end, whose area is a. Assuming frictionless flow, determine (i) the height h to which the water rises in the piezometer...
  9. T

    Fluids at Rest: Pressure/Force Problem

    This question has been asked several times, but I don't want the answer (I can see the stupid answer...) I need help with my solution... Homework Statement A large aquarium of height 5.00m is filled with fresh water to a depth of 2.00m. One wall of the aquarium consists of thick...
  10. D

    Fluids design problem - piping layout

    Homework Statement The picture is what the prof. gave us. It isn't the most understandable but I will try my best to describe what's going on. As the picture shows it is a top view of the layout. The big blob on the left is a large reservoir where elevation is not needed. v, v1, v2, v3 are...
  11. S

    How can the required force to open the gate be calculated?

    Hi, I need help with a fluid mechanics question: A 1.5m-diameter floodgate placed vertically is 6m below the water level at it's highest point. The gate is hinged at the top and opens into the reservoir. Calculate the required horizontal force applied at the bottom of the gate in order to...
  12. C

    Fluids, pressure on a wall to determine max depth

    Homework Statement A square pool with 100-m-long sides is created in a concrete parking lot. The walls are concrete 90 cm thick and have a density of 2.5 g/cm3. The coefficient of static friction between the walls and the parking lot is 0.49. What is the maximum possible depth of the pool...
  13. X

    Fluids Problem help invovling floating

    Homework Statement A racquetball with a diameter of 5.6 cm and a mass of 42 g is cut in half to make a boat for American pennies made after 1982. The mass and volume of an American penny made after 1982 are 2.5 g and 0.36 cm3. How many pennies can be placed in the racquetball boat without...
  14. P

    Vacuum and non-vacuum regions, dust and fluids

    In GR there is made a clear distinction between a vacuum region and a non-vacuum region as one is handled by the Ricci tensor and the other by the Weyl tensor. But is reality so black and white? And when do we realistically talk about dust and when about fluid? So the inside of an average...
  15. K

    Understanding Buoyancy: Calculating Mass of a Ship in Different Fluids

    53 ••• [SSM] A ship sails from seawater (specific gravity 1.025) into freshwater, and therefore sinks slightly. When its 600,000-kg load is removed, it returns to its original level. Assuming that the sides of the ship are vertical at the water line, find the mass of the ship before it was...
  16. K

    Calculating Thickness of Copper Cladding on Zinc Pennies | US Mint 1983-Present

    26 ••• Since 1983, the US Mint has coined pennies that are made out of zinc with a copper cladding. The mass of this type of penny is 2.50 g. Model the penny as a uniform cylinder of height 1.23 mm and radius 9.50 mm. Assume the copper cladding is uniformly thick on all surfaces. If the density...
  17. K

    Calculating Volume and Weight of Water in a Cone Jar: Fluids (Pressure)

    The volume of a cone of height h and base radius r is V = πr2h/3. A jar in the shape of a cone of height 25 cm has a base with a radius equal to 15 cm. The jar is filled with water. Then its lid (the base of the cone) is screwed on and the jar is turned over so its lid is horizontal. (a) Find...
  18. K

    Can Fluids Flow from Low Pressure to High Pressure?

    I maintain that not only they can, but that observations illustrating the phenomena are common. To keep the thread from fragmenting too badly, I should like to propose the following rules of discussion: 1) Liquids shall be limited to water and air. 2) Only natural flows may be offered...
  19. N

    Fluids question - Pump flowrate ofdue to elevation head

    Hey guys, I've been strugling with a concept recently and was hoping someone familiar with fluid dynamics could answer. I am trying to calculate the flowrate of a flow circuit with a given pump. I have the pump performance curve (flow vs. head) of the pump and I know all the given pipe...
  20. S

    IB student, Urgently on extended essay(Non Newtonian fluids)

    Hi, guys. I'm doing an extended essay in physics for the IB diploma program. The extended essay is a 4000 word research project on a topic of your choice, and I have opted to do mine in physics. I'm having a lot of trouble narrowing down a suitable research question, and at this point, I have...
  21. I

    Simple fluids pressure question

    Hello friends I am again in need of some asistance, The Question is as follows: The pressure head in a gas main at a point 120 m above sea level is equivalent to 180 mm of water. Assuming that the densities of air and gas remain constant and equal to 1.202 kg m^-3 and 0.561 kg m^-3...
  22. P

    Viscosity of fluids effect on it's splashes?

    Hi all, i'm doing a research essay on how the viscosity of a fluid affects it's splashes. i'm currently stuck and do not know how i should approach this theoretically. i have no problem with the practical (filling up balloons with the fluid and dropping them from a height to see the splash...
  23. T

    Air Compressor + CTIS (Fluids)

    Hi, I have a fluid dynamic question. I need to know the volume airflow rate (cfm) for head loss calculations in my CTIS (central tire inflation system). My goal is to use this info to come up with an analytical model of the system. Our facility has an air compressor that is set to 72 psi...
  24. Femme_physics

    Fluids mechanics is also gas mechanics?

    "Fluids mechanics" is also gas mechanics? This bothers me a bit: Gases? You include in the chapter of "fluid mechanics" gases? These are two different states. Why not have a field called Gas mechanics? And if you want, call the entire field "Fluid-gas mechanics".
  25. S

    How Fast Should Water Flow from a Faucet to Properly Water a Rooftop Lawn?

    Homework Statement A man has a garden on the roof of his building. He has a patio and a small lawn. He wants to water the lawn. He has a sprinkler in the form of a disk with 40 holes of diameter 1 mm. A line drawn tangent to the sprinkler at the location of the outer most holes would make an...
  26. N

    Heat transfer in fluids, Comsol 4.0a

    Homework Statement hi there, I'm working on an annealing furnace. ingots are warmed up in the oven. I'm doing this with a finite elements method called Comsol Multiphysics. This is a pretty complex software program. Can someone please help me with this part of ComsolHomework Equations it is...
  27. B

    Simple Fluids Problem: Cylinder on Oil with Added Weight

    Homework Statement A cylindrical disk of wood weighing 47.0 N and having a diameter of 30 cm floats on a cylinder of oil of density 0.850 g/cm^3 (the figure). The cylinder of oil is 75.0 cm deep and has a diameter the same as that of the wood. a) What is the gauge pressure at the top of the...
  28. B

    Fluids (Through an IV) Question

    Hi everyone, just some background information--I work in an emergency department as a trauma tech. My co-workers and I got into discussion at work about the fastest method of giving a patient fluid via an IV. We had this really sick patient who needed multiple liters of fluid and I was wondering...
  29. L

    (Fluids) Material and local velocity and acceleration fields.

    Homework Statement The streamlines of a fluid are as follows: x = (x0) + 3(y0)t^2 y = (y0)/(1 + 2t) z = (z0) + 5(x0)t Find the velocity and acceleration fields in the Eulerian description (local). Homework Equations Total/material acceleration: Dv/Dt = dv/dt + v.grad(v) The...
  30. A

    Fluids, finding the density of a sphere in oil Please help

    Homework Statement A small sphere (diameter = 10 mm) is left to fall in a fluid (oil, SAEIOW) at 200 degrees with a constant velocity of 50 mm/s.. The Following data is available: - For SAEIOW oil at 20 degrees: p = 920 kg/m3, μ = 0.1 Pa.s a) The drag force on the sphere b) The...
  31. D

    Conceptual Question Regarding Fluids

    Homework Statement A friend and I were arguing about how tension created by a submerged ball affects the total weight of the container. Homework Equations I couldn't find anything similar to the situation, so I drew a quick picture to better illustrate the situation :D A string is...
  32. Telemachus

    Idel van der Waals fluids and Helmholtz potential

    Homework Statement Hi there. I have this problem which I'm trying to solve. Its from callen, it says: Two ideal van der Walls fluids are contained in a cylinder, sparated by an internal moveable piston. There is one mole of each fluid, and the two fluids have the same values of the van der...
  33. A

    Fluids Mechanics, Wall shear stress, Velocity, Fricition Example

    Homework Statement A two-dimensional incompressible flow takes place in the space between two parallel solid plane boundaries, which are a distance 2b apart. The density of the fluid is p, the dynamic viscosity is p. and the velocity distribution in the flow is given by the expression I...
  34. S

    Calculating Resultant Force of 2 Fluids in a Tank

    1. A tank with vertical walls, 2m wide and 2m long and 2.5m high, is filled with 4800 litres of water (density 1000 kg/m3) and 3200 litres of light oil (density 900 kg/m3). Calculate the magnitude and location of the resultant force on each of the vertical walls of the tank. 2. By doing some...
  35. K

    What is the Critical Radius in Fluid Dynamics?

    Homework Statement http://img571.imageshack.us/i/reaction.png/ Homework Equations Velocity = (R^2-r^2) * dP/(4nL) VMax = R^2 * dP/(4nL) Average velocity = R^2 * (dP/(L*8n)) dP= change in pressure n = viscosity The Attempt at a Solution Average velocity = R^2 * (dP/(L*8n))...
  36. F

    How Can Buckingham's Pi Theorem Be Used to Describe Waves Amplitude?

    Homework Statement Use Buckingham's Pi Theorem to describe waves amplitude. The Attempt at a Solution Waves amplitude depends on: Geometric variables: L,A Kinematic variables: g,c (c = waves speed) Dynamic variables: roh (density), sigma (surface tension) Using MLT: L = L, A =...
  37. F

    Can someone explain this fluids formula to me?

    Homework Statement The question pertains to hydrostatic lifts. So, assuming you have a lift and you're applying pressure to one side and the other side is rising: P0 + P1 = P0 + P2 + (rho)gh Now, when we look at the equation, why is it (rho)gh? I'm thinking it's something like mgh, so to...
  38. ?

    Acceleration of magnetic fluids

    Is it possible to use a linear accelerator to fire a magnetic fluid. I have this idea for a science fiction story that uses a coil gun and liquid oxygen for rocket propulsion. Is this feasible? As always thank you for your input.
  39. F

    How High Will the Ball Shoot Above the Water?

    Homework Statement A 1.06 kg hollow ball with a radius of 0.113 m, filled with air, is released from rest at the bottom of a 1.94 m deep pool of water. How high above the water does the ball shoot upward? Neglect all frictional effects, and neglect the ball's motion when it is only partially...
  40. E

    "Calculate Resultant Force on Vertical Dam Wall

    Homework Statement Pressure_2.jpg: http://www.imageupload.org/thumb/thumb_8609.jpg A vertical dam wall has a width w. Water is filled to a height H behind the dam. Calculate the resultant force on the dam wall. Homework Equations P=F/A P= Pa + p*g*h The Attempt at a...
  41. S

    Fluids - Conical vs Cylindrical Water Clock

    I am researching water clocks through history. At some point, it was realized that for the container the water drips from, a conical container with the hole at its point was superior to a cylindrical container with the hole in its side. Could someone explain to me why conical containers are...
  42. D

    Does Fluid Near Solid Interfaces Move Faster Due to Viscosity Differences?

    Hi all, This is my first post and my background is in Computer Science, so pardon me if my terminology is not correct or even I sound ignorant Physics-wise :) Anyways, I implemented a semi-Lagrangian based Navier-Stokes (NS) solver and it's running smoothly on a CUDA-capable GPU and I...
  43. C

    Pressures on fluids of mercury and water

    Homework Statement Can someone please explain to me why P3-P1=Pb-Pa? [PLAIN]http://img694.imageshack.us/img694/8123/45074508.jpg thank you
  44. S

    Pressure & Fluids: Questions Answered!

    Homework Statement Hi, this morning in the school lab we did experiments about pressure and I've some questions., could you help me? thanks! If I fill a glass with water the atmospherical pressure press on water on top of glass because it is in contact with air, but does atmospherical...
  45. M

    Weighing fluids with immersed objects

    So imagine that in an open room you have a big scale and on it you have a jar and a lid sitting next to each other. Imagine a butterfly floating into the jar but not touching the bottom. I wouldn't think this would increase the reading on the scale. But if you put the lid on the jar, closing the...
  46. P

    Simple fluids but is the application correct

    Homework Statement problem states that ... there is a u tube and filled with liquid of densities ρ and 2ρ. the base length of the tube is 'l'. now it is accelerated towards right with accl.=a. if the HEIGHT DIFFERENCE AFTER ACCELERATING THE SYSTEM IS '0'. then what was the height difference...
  47. D

    Fluids Book: Find Upper Level Undergrad Resource

    Hi, I'm taking an upper level ungergrad fluids class and am struggling with it, does anyone know a good book or other resource to help get a better understanding of the subject (one with lots of examples and problems preferably). Needs to cover topics like dimensional analysis, Stokes flow...
  48. D

    Fluids - boundary conditions for rotating sphere

    Homework Statement A sphere under uniform rotation R, in a simple shear flow, given at infinity by ui = G(x2 + c)deltai1 The centre of sphere is fixed at x2 Boundary conditions are ui = EijkRjxk on sphere, and ui = G(x2 + c) at...
  49. H

    Non Newtonian Fluids: Why & How Do They Respond to Stress?

    Why do non Newtonian fluids such as the cornstarch and water mixture respond to stress the way they do? What prompts the atoms to come together to resist the force?
  50. A

    I with questions on using energy, thermal properties and fluids and density

    Im working on test corrections that are due tomorrow, and I was out sick for around a month and a half or so. I have been trying to find these in our book, however, our book is pretty much a big hunk of annoying weight that should be used for a campfire. Anyway, I am looking for some help with...
Back
Top