# What is Viscosity: Definition and 251 Discussions

The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.Viscosity can be conceptualized as quantifying the internal frictional force that arises between adjacent layers of fluid that are in relative motion. For instance, when a viscous fluid is forced through a tube, it flows more quickly near the tube's axis than near its walls. In such a case, experiments show that some stress (such as a pressure difference between the two ends of the tube) is needed to sustain the flow through the tube. This is because a force is required to overcome the friction between the layers of the fluid which are in relative motion. So for a tube with a constant rate of flow, the strength of the compensating force is proportional to the fluid's viscosity.
A fluid that has no resistance to shear stress is known as an ideal or inviscid fluid. Zero viscosity is observed only at very low temperatures in superfluids. Otherwise, the second law of thermodynamics requires all fluids to have positive viscosity; such fluids are technically said to be viscous or viscid. A fluid with a high viscosity, such as pitch, may appear to be a solid.

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1. ### A Navier-Stokes solutions: Beltrami flow

There are some known solutions for 3D Navier-Stokes such as Beltrami flow. In the literature these Beltrami flow solutions are said to not take into account viscosity, however when I read the information on Beltrami flow, they do seem to involve (kinematic) viscosity: From incompressible...
2. ### Viscosity by Falling Sphere Equations

I have recently conducted an experiment to measure the viscosity of some liquids using the falling sphere method and a high-speed camera. I used different diameters of sphere starting from 2.5, 5, 10, 15 and 20 mm. What I want to prove using stokes law equation is that diameter of sphere doesn't...
3. ### Understanding CVT Fluid Viscosity and When to Replace: Expert Insights

I went to Subaru for period maintenance checkup. They told me the car was due for CVT fluid replacement which was done every 5 years or 40,000 miles. It's already 7 years even if the mileage is only below 20,000 miles so I let them go ahead. The service advisor told me as time passes, the...

Hi Physics Forums, I'm wondering why Newton's Law of Viscosity sometimes has a negative sign in front of the viscosity and sometimes it doesn't? Thanks for your help!
5. ### B Does the density of a liquid affect the braking of an object in free fall when it lands?

In mine hypothesis I want to slow down free fall for diffrent density objects in liqudies. I have a stone wich i roughly a denisty of 2,7 g/ml and gold with 19,7 g/ml. They have the same size. Liquied glucose has the density of roughly 1,5 g/ml. In my example, I drop at the same time in a 1...
6. ### Viscosity and resonant frequency?

AP french's formula -> https://docs.google.com/document/d/13j2bIFgifZFLm65f4j6Wg9CI4sFxqEoDSIMCgCrWr9o/edit?usp=sharing Temperature relation that i couldnt understand ->...
7. ### A Can you help to solve this integral? (resin viscosity research)

I have tried WolfarmAlpha but it could help me. Please note this is not a homework exercise. I am a researcher and I am looking to model viscosity development of resin. there I came across with this express :) $$\int{\frac{1}{a\cdot e^{bx}+c\cdot e^{kx}}dx}$$
8. ### I Relationship between viscosity and velocity in fluid mechanics

hello, I read in a lecture paper about fluid mechanics that velocity is not related to viscosity, i found this odd and i think it is an error , can someone confirm that?
9. ### Viscosity in lubricating fluid in the bench-guide of a machine

Figure: bench (bancada), guide (guide), oil (aceite). My attempt at a solution: $$\textrm{extension } L=0,6\, \textrm{m}$$ $$F=1500\, \textrm{N},\,\, c=0,1\, \textrm{m}/\textrm{s},\,\, h=0,0001\, \textrm{m}$$ $$v=5\, \textrm{stoke}=0,0005\, \textrm{m}^2/\textrm{s},\,\, \rho_r=0,9$$ a)...
10. ### Inconsistent flow rate measurements of an engine diesel fuel

I am measuring the volumetric flow rate of a diesel fuel using "Turbines" flow meter, both in the supply and return fuel lines of an industrial diesel engine (https://www.cat.com/en_US/products/new/power-systems/industrial/industrial-diesel-engines/18398034.html – coupled with a generator for...
11. ### Calculating force on a syringe plunger for a viscous fluid?

I'm currently working on a precise glue/resin dispenser, and I'm trying to derive an equation for the force one must exert on a syringe plunger as a function of the desired flow rate Q, and also accounting for the fluid viscosity and the syringe barrel and needle geometry. I've attached a scan...
12. ### I Analytically Solving the Magnus Effect with Viscosity in Ball Flight Simulation

I am trying to add to a problem of mine the viscosity parameter, simulating the fly of a ball. However I obtain the following equations d^2V_z/dt^2 = WdV_z/dt - dV_x/dt and d^2V_x/dt^2 = WdV_x/dt - dV_z/dt where W is a function linearly dependant to t. Any ideas how I could analytically solve...
13. ### B Terminal Velocity Equation in vertical cylinder with some fluid

I just have a question that could you guys make an equation that expresses the terminal velocity based on followed condition? - When diameter increase, velocity decrease - velocity should change depending on both cylinder and sphere's diameter - We know every variable - The sphere is in...
14. ### I Fluid Viscosity & Viscous Friction Between Plates

When fluid is placed between two parallel plates such that one plate is moving and other is stationary, fluid will start flowing. Between plate and the fluid there is viscous friction given by equation: $$F = -\eta A \frac {dv} {dy}$$ where $\eta$ is fluid viscosity, $A$ is area of a plate...
15. ### B How Does Viscosity and Turbulence Affect Fluid Flow Between Plates?

https://openstax.org/books/university-physics-volume-1/pages/14-7-viscosity-and-turbulence I am trying to understand the derivation from Figure 14.36 which starts with " The fluid to be measured is placed between two parallel plates. The bottom plate is held fixed, while the top plate is moved...
16. ### Can turbulence help measure liquid viscosity more accurately?

Hi, all. Recently I plan to participate in an physics competition which focuses on viscosity measurements of liquid~I’ve investigted some kinds of methods such as capillary viscometers, Rotational viscometers, Vibrating Viscometers, co-flowing laminar viscometers and so on. I hope to find a...
17. ### How do I get the viscosity of a mash mixture in brewing?

Hi, I am designing a mash tun to produce beer. I have 1300kg of malted barley (at a known density) and 3250kg of water. Please could someone outline a method I could use as I am really struggling. One of the main problems I am having is accounting for the density change of the malt when it...
18. ### Finding the coefficient of viscosity

"Calculate the gradient (or slope) of the line and use this and the equation above to calculate the value for the viscosity, η. You MUST use the gradient to calculate the viscosity." here are the results: I'm not sure if it's just me who finds this confusing

49. ### B What property of a fluid determinates rising and sinking Velocities

If we have a bottle with a fluid A of X density, and in the bottom of this bottle it magically spawns the same amount of fluid B with X/2 density, fluid B should rise in fluid A until they both change positions and fluid B floats in A. Wich property of the fluids are the ones that determinates...
50. ### How sodium alginate changes the viscosity in water?

Hello everyone. I have a question about the sodium alginate (NaC6H7O6)n. Recently, sodium alginate is widely used for fabricating edible bottle. And I also try to utilize sodium alginate for controlling the viscosity of water. I found that with small amount of sodium alginate powder in DI water...