Solving Pipe Flow: Understanding Why $\tau =\mu(-dV/dR)$

AI Thread Summary
The discussion centers on the shear stress formula τ = μ(-dV/dR) in pipe flow, emphasizing the role of the negative sign. This sign indicates that velocity is measured as a function of distance from the centerline of the pipe, rather than the wall. When considering velocity from the wall, the distance can be treated as positive, leading to confusion about the sign. Participants clarify that the negative sign is necessary to maintain consistency in the direction of velocity gradient. Understanding this concept is crucial for accurately analyzing fluid flow in pipes.
foo9008
Messages
676
Reaction score
4

Homework Statement


why the shaer stress ( tau) formula is given by μ(dv/ dy ) = μ(-dV / dR) , why there is a negative sign there ?

Homework Equations

The Attempt at a Solution

 

Attachments

  • IMG_20160421_125023[1].jpg
    IMG_20160421_125023[1].jpg
    32.8 KB · Views: 462
Physics news on Phys.org
The negative sign is included because you are considering the velocity as a function of the distance from the center line of the pipe, not from the wall.
 
  • Like
Likes foo9008
mfig said:
The negative sign is included because you are considering the velocity as a function of the distance from the center line of the pipe, not from the wall.
why when we are considering the velocity as a function of the distance from the the wall , it's positive ? or we can also consider the distance from the wall as positive ?
 
mfig said:
The negative sign is included because you are considering the velocity as a function of the distance from the center line of the pipe, not from the wall.
can we consider the distance from the centerline of pipe to wall as positive ?
 

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
View full post »

Similar threads

Reynold's Number: Understanding Laminar Flow in Smooth Pipes
Replies
1
Views
1K
Laminar Flow : shear force on walls
Replies
1
Views
1K
Calculating Oil Flow Rate in Cast Iron Pipe
Replies
5
Views
1K
Flow Velocity- Guranteed to be Laminar
Replies
2
Views
2K
Is the Flow Laminar or Turbulent? Determining with Reynolds Number
Replies
1
Views
3K
Power required to rotate a disc in a fluid
Replies
2
Views
2K
Kinematic viscosity depends on pressure
Replies
3
Views
2K
What Exhaust Pipe Diameter is Needed for a Given Exhaust Speed?
Replies
1
Views
2K
Pressure and Flow Rate in a Tank
Replies
10
Views
3K
How Does Bernoulli's Principle Apply to Varying Pipe Diameters and Water Flow?
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top