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".

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  1. C

    Fluids - A lost shipping container is found resting on the ocean floor

    Homework Statement A lost shipping container is found resting on the ocean floor and completely submerged. The container is 6.3 m long, 2.1 m wide, and 2.6 m high. Salvage experts attach a spherical balloon to the top of the container and inflate it with air pumped down from the surface...
  2. B

    How Is Air Pressure Calculated in a Crushed Can Experiment?

    Homework Statement A rectangular metal can with dimensions of 0.234 meters by 0.194 meters by 0.143 meters is used in a physics demonstration to show the force exerted by air pressure. A small quantity of water is poured into the can and brought to a boil. Then the can is capped and allowed...
  3. A

    Bernoulli's principle- fluids ?

    bernoulli's principle- fluids...? Homework Statement http://img30.imageshack.us/img30/4119/45086777.jpg Homework Equations A1V1=A2V2 P2+1/2pv1^2 = p1+1/2pv2^2 P+1/2mv^2 + pgy = constant The Attempt at a Solution V2=A1*V1/A2 1/2*p*A1^2*V1^2*p*g*h/A2^2=1/2pv1^2 2*g*h*A1^2V1^2/ A2^2=V1^2...
  4. D

    Fluids Question Regarding Density

    Homework Statement A spherically shaped balloon has a radius of 11.5 m, and is filled with helium. How large a cargo can it lift, assuming that the skin and structure of the balloon have a mass of 1200 kg? Neglect the bouyant force on the cargo volume itself. Homework Equations Fb =...
  5. J

    Compressible Fluids: Getting Desired Volume/Mass Flow Rate

    I'm having trouble calculating the required pressure to get the desired volume flow rate (at outlet conditions). I'm no expert at compressible fluid systems, but I ended up being the one to design it... The system must feed helium vertically through 3/8" ID, 112 ft long tubing (ID can vary, I...
  6. R

    Fluids- hydrodynamic interactions

    If we consider a system of N suspended particles diffusing through a narrow channel. What happened if the hydrodynamic interactions are neglected? Is there only flow? How can the particles diffusse without flow?
  7. D

    Why isn't MatPIV fit for non-Newtonian fluids?

    We are using the MatPIV Matlab toolkit: http://www.math.uio.no/~jks/matpiv/ However, we are having trouble using the toolkit with viscoplastic media. It was expected to find a yielded region and a unyielded region, however, from the results of MatPIV it appeared that the whole area was...
  8. G

    Trying to find some rheostatic fluids

    I'm trying to do this demonstration for a high school class: Using different shapes of "boats" I'm going to demonstrate how each boat shape affects the flow of water across it - does the water glide smoothly around the boat or become turbulent? My professor briefly mentioned that "rheostatic...
  9. T

    What Height of Water in a Long Arm Risks Popping the Seal?

    Homework Statement The plastic tube has a cross-sectional area of 5.00 cm². The tube is filled with water until the short arm (of length d = 0.800 m) is full. Then the short arm is sealed and more water is gradually poured into the long arm. If the seal will pop off when the force on it...
  10. N

    Solving Fluids Questions: Helium-Filled Balloon & Sealed Spherical Shell

    Homework Statement A helium-filled balloon is tied to a 2.00-m-long, 0.0500-kg uniform string. The balloon is spherical with a radius of 0.400m. When released, it lifts a length h of string and then remains in equilibrium, as in the figure. Assuming envelope of the balloon has mass 0.250...
  11. P

    How Do I Solve These Challenging Fluid Mechanics Problems?

    I stucked with my hard fluid questions. I don't know what should I do first. So, Please describe detail as much as possible. Thanks for Physics Genious guys. 2. A house at the bottom of a hill is fed by a full tank of water 5.0m deep and connected to the house by a pipe that is 110m long...
  12. F

    Gas compression and Interaction with Fluids

    I have been trying to find out how to calculate a number of things in a system involving liquid and gas. In the attached diagram there is a U-bend with gravity acting down on it. If one side is sealed with a plunger and the other side is filled with a fluid (L) we would end up with the...
  13. P

    How Do You Calculate the Force on Different Faces of an L-Shaped Water Tank?

    Homework Statement The L-shaped tank shown in Fig. 14-33 is filled with water and is open at the top. If d = 3.24 m, what is the force due to the water (a) on face A and (b) on face B? IMAGE: http://edugen.wiley.com/edugen/courses/crs1650/art/qb/qu/c14/fig14_33.gif Homework Equations i...
  14. S

    Calculating Charge Density in Fluids

    How would one determine the charge density of a fluid? I'm using the equation of I = qnvA . Amperes = charge of electron * charge density * velocity * Area. The only thing I'm not sure of is how to determine charge density. I've read several websites and I have a few textbooks here...
  15. K

    Solve 0.3m Diameter Cork Ball Drag Question in River

    Homework Statement A 0.3m diameter cork ball (density 210kg/m^3) is tied to an object on the bottom of a river as is shown in fig B3. The weight of the cable and the drag on it can be neglected. Assume the water viscosity u is 1.12x10^-3 Ns/M^2 and the water density p is 1000kg/m^3, and the...
  16. K

    What is the Gauge Pressure Just Downstream of a Fan in a Duct System?

    Homework Statement A duct system that exhausts air of density 1.2kg/m3 from a building out into the atmosphere is shown in fig. A2 (attachment). The air flow is driven by a fan across which is a monometer that reads 2 cm of water. The cross sectional areas of the upstream and downstream...
  17. Saladsamurai

    How do I incorporate theta into the momentum equation for Fluids homework?

    Homework Statement Homework Equations \sum(\dot{m}\vec{v})_{exit}-\sum(\dot{m}\vec{v})_{inlet}=\sum F_{ext} I only know that this is cons of momentum because my prof told us. I am having a hard time visualizing how to incorporate THETA into the above equation since it is not a...
  18. V

    Why do fluids expand with heat? explaining covection currents

    I'm guessing it has something to do with the fluid gaining thermal energy from the heat, the heat makes the molecules repel each other further so the fluids volume expands? if not why do fluids expand with heat? - the rest is mandatory, after expanding the volume increases, decreasing the...
  19. K

    Calculating Pipe Discharge from Fluid Velocity Diagram | Tips and Tricks

    does anyone know how to go about calculating discharge from a velocity diagram of flow in a pipe? thanks for anyhelp
  20. V

    Fluids Conceptual Questions: Understanding Pressure and Bernoulli's Equation

    Homework Statement 1. Is pressure always force/area? or is it only for static fluids? 2. I read that the equation for hydrostatic pressure is (initial pressure) + density x gravity x height, but How would I know to use that instead of Force/Area? Also is the initial pressure always atmospheric...
  21. M

    Pressure in Fluids: Why Does It Act in All Directions?

    I've read (and experienced!) that pressure in fluids acts in all directions. Why is it so? I understand that if you dive 5 meters down in the water, the water's weight is greater than 1 meter below water surface. So if I'm standing up there under the water, I should feel a greater pressure on...
  22. A

    Hydraulic, Fluids at Rest Problem (barrel)

    Homework Statement In the figure below, an open tube of length L = 1.8 m and cross-sectional area A = 4.6 cm2 is fixed to the top of a cylindrical barrel of diameter D = 1.2 m and height H = 1.8 m. The barrel and tube are filled with water (to the top of the tube). Calculate the ratio of the...
  23. V

    Conceptual Questions Fluids and Simple Harmonic motion

    Homework Statement 1. Do you use the equation of continuity and Bernoulli's equation simultaneously in a question? When do you use them? 2. In simple harmonic motion, why is the velocity shifted to left of the displacement by pi/4? Homework Equations pressure + .5density x velocity...
  24. J

    Need Help with a Basic Fluids Problem - Buoyancy and Archimedes' principle

    Good afternoon, I am having some trouble solving this basic fluids problem, and I am hoping you can look over my work, and offer some assistance. Homework Statement A submarine has a total mass of 2.1 multiplied by 10^6 kg, including crew and equipment. The vessel consists of two parts...
  25. N

    Pressure of Fluids - Questions & Answers

    Hi all. There's a couple of things I have thought about, and I hope you can clarify this for me. 1) In Torricelli's experiment with the tube and mercury, the vacuum-part in the tube has zero pressure (as vacuum always does). Does this mean that it is never possible to "suck" the mercury out of...
  26. M

    Head of fluids & Engine Efficieny.

    Homework Statement A pump delivers water at a rate of 60L/s with a head of 65m. It runs for 8 hours per day. The efficiency of the pump is 75%. The efficiency of the electric motor driving the pump is 80%. i) What is the value of the head in kPa ii) Calculate the input power kW that is...
  27. J

    Fluid Dynamics: Calculating Force on Hemisphere in Uniform Flow

    Homework Statement A sphere of radius a is surrounded by a fluid, flowing with a uniform velocity U far from the sphere. Imagine the sphere divided into two hemispheres by a plane perpendicular to the direction of flow. Calculate the force on each hemisphere, assuming the pressure far from...
  28. M

    Confusion about relativistic fluids

    According to Schutz book, in special relativity general fluids in the MCRF (Momentarily Commoving Reference Frame) are characterized by no bulk flow of the fluid element and no spatial momentum in the particles. The energy-momentum tensor elements T0i (flux of energy across i-surface) are not...
  29. W

    What is the Relationship Between Shear Stress and Density for Fluids?

    Homework Statement I have an empirically-derived equation for the shear stress of a fluid on a surface, given by the equation below. I am supposed to take the derivative of density with respect to distance, and I must use this equation to find an expression for density. Delta = Boundary...
  30. P

    Regarding Fluids and hydrostatic force ratios

    http://img255.imageshack.us/img255/7909/hrw71431.gif http://g.imageshack.us/img255/hrw71431.gif/1/ An open tube of length L = 1.8 m and cross-sectional area A = 4.6 cm^2 is fixed to the top of a cylindrical barrel of diameter D= 1.2m and height H=1.8 m The barrel and the tube are filled with...
  31. L

    Calculate Shear Stress on a Plate Moving Through Oil | Fluid Mechanics Homework

    Homework Statement A plate sitting on the surface of oil with thickness (y) and viscosity (u) moves with speed (Vo). The velocity profile is a parabola with oil at the plates having the same velocity as the plates. Find the shear stress on the plate from the oil. Repeat problem but with a...
  32. 4

    How Is Stagnation Pressure Calculated for an Airplane Wing at Altitude?

    Homework Statement When an airplane is flying 200mph at 5000-ft altitude in a standard atmosphere, the air velocity at a certain point on the wing is 273 mph relative to the airplane. What suction pressure is developed on the wing at that point? What is the pressure at the leading edge ( a...
  33. D

    Pressure and Forces within Fluids

    Tank A |...| |..h2o...| |..h2o...| |_h2o__| Tank B \.../ .\..h2o../ ..\.h2o./ ...\h2o/ Tank C .../...\ ../.h2o.\ ./..h2o..\ /__h2o__\ The three tanks shown above are filled with water to an equal...
  34. J

    Calculating Forces on a Tank with Flat Ends Using Integration

    I am working on the problem below that is confusing me. I am not sure of how to approach the center of pressure and resultant force. I attempted the problem using the formulas for a rectangular wall but I am not sure if its right. The problem asks for the pressure acting against the FLAT ends...
  35. C

    How Do You Calculate the Density of a Mud Mixture?

    Homework Statement A typical mud is compsed of 76 wt% sand and 24 wt% water. What is the density? Homework Equations No relevant equations but density of sand is 951 kg/m^3 and 1 kg/m^3 for water. The Attempt at a Solution Just multiplied the density by the percentage and added...
  36. S

    Electrical Conductivity of Fluids

    So it has always been my understanding that in order for something to electrically conductive it has to have more electrons than it needs. If the electrons can be easily shaken from their atoms, then it's conductive. The easier it is for the electron to move to the next atom the more conductive...
  37. D

    Calculate Force on Submarine Hatch due to Seawater Pressure

    Homework Statement A submarine is at a depth of 500 m under the water. The force on a circular hatch of 1.00 m in diameter due to the seawater (density = 1,025 kg/m3) pressure from outside the submarine is: Homework Equations F=PA P2-P1=pgd The Attempt at a Solution F=(pgd+P1)A...
  38. S

    Is It True That Ideal Fluids Always Flow from High Pressure to Low Pressure?

    What's wrong with this statement: 'Ideal fluids always flow from high pressure to low pressure'? Could someone give me an example of where this is not true?
  39. T

    Fluids at rest: two connected cylinders

    Homework Statement [This probably seems really easy to the physics whizzes out there but...*blushes*] Two identical cylindrical vessels with their bases at the same level each contain a liquid of density 1.30x103 kg/m3. The area of each base is 4.00cm2, but in one vessel the liquid height is...
  40. R

    What is the minimum force needed for a syringe to deliver serum into a patient?

    Homework Statement I'll just post the question given: You are at the clinic getting your flu shot. The syringe that is being used to deliver the vaccine has a volume of 2.0 mL, an inner diameter of 6.0 mm, and the needle has an inner diameter of 0.25 mm. The plunger on which the nurse has...
  41. L

    Did I do this fluids problem right? A find the gallons/min gushed by a fountain

    1. A fountain sends a stream of water straight up into the air to a maximum height of 4.23 m. The effective area of the pipe feeding the fountain is 5.38 x 10^-4 m^2. Neglecting air resistance and any viscous effects, determine how many gallons per minute are being used by the fountain. (1 gal =...
  42. fsteveb

    Researching ball falling into fluids

    I want to write a opengl (graphical) representation of a non-deformable ball or other shape in general being dropped onto a liquid surface. The surface will consist of a grid with surface maps. So I need to calculate I assume the wave equation in response to the object impact. Once I get the...
  43. N

    Explaining Low Frequency and Longitudinal Waves in Fluids

    seeking help..please why do low frequency contributes a low pitch?how?& why only longitudinal in fluids?can any1 please explain to me,tq please..:smile:
  44. J

    Heights of fluids in a u-tube?

    Homework Statement Glycerin is poured into an open U-shaped tube until the height in both sides is 36 cm. Ethyl alcohol is then poured into one arm until the height of the alcohol column is 30 cm. The two liquids do not mix. What is the difference in height between the top surface of the...
  45. D

    Flow of fluids through an infinitely thin hole

    Every student knows the flow through a long tube ignoring end effects but my "A" level son has asked if there is a formula for the flow of a fluid through a this hole (or out of a bucket with a hole at the bottom). I think such a formula would include surface tension, viscosity and other...
  46. M

    Solving Blood Pressure Problem with Fluids: Pressure

    Fluids -- pressure Blood plasma flows from a bag through a tube into a patient's vein, where the blood pressure is 10 mmHg. The specific gravity of blood plasma at 37°C is 1.03. What is the minimum elevation the bag must have so the plasma flows into the vein? Prof gave this problem for us...
  47. O

    What Are Some Optimal Pipe Diameter Solutions for a Dual-Valve Fluid System?

    Hey guys, I am studying in heriot watt university Dubai. I would like to be a Fluids expert. I have been doing well in my course-works and my professor usually helps me around to get a few extra info. However recently due to a tight schedule he is unable to help me out. I have managed to...
  48. J

    What is the profile of the second fluid in laminar flow with two fluids?

    Hi I am working in an application where we pump a fluid in a water -filled tube, where the second fluid has a viscosity of 3-4 times the viscosity of water. We have laminar flow (Re around 20). If the fluids were 100% compatible (e.g. colored water vs clear water) I have determined that...
  49. S

    . Air and water in a cross flow heat exchanger. The fluids do not come

    Hi, I am trying to do a cross flow analysis in FLUENT. Air and water in a cross flow heat exchanger. The fluids do not come in contact. I have modeled and meshed the geometry in GAMBIT. Could someone pls help me with the steps in FLUENT as to how to assign different fluid properties for...
  50. Y

    How do I solve for w and p in an incompressible flow using Euler's equation?

    I'm stumped on a HW question that I just can't seem to proceed on. Homework Statement An incompressible ( rho = constant ) flow in 2 dimensions [x = (x,z)], with F = (0,-g), satisfies Euler's equation. For this flow, the velocity is u = (u0,w(x)), where u0 is a constant, with w = 0 on x...
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