B Fluid Continuity Equation in different reference frame

Click For Summary
The discussion centers on the application of the continuity equation in fluid dynamics, specifically regarding changes in fluid velocity and cross-sectional area. When fluid velocity increases, the area must decrease to maintain continuity, but switching to a different reference frame complicates this relationship. The key point is that the area constriction is relative to the tube's reference frame, not an arbitrary frame of reference. Understanding this is crucial for correctly applying the continuity equation. The derivation of the continuity equation clarifies these relationships and resolves the apparent violation.
versine
Messages
24
Reaction score
5
If I have fluid with area 10 and velocity 10, if the velocity increases to 20 the area will become 5. But if we switch to a reference frame moving at velocity 1 opposite this motion, then it would be 10 and 11 to 5 and 21, violating the continuity equation. What is wrong?
 
Physics news on Phys.org
If I understand what you ask correctly, the area is constricted because the fluid is moving through some tube. If that's the case, it's the velocity relative to the tube's reference frame that counts. You will see why if you follow the derivation of the continuity equation.
 
Reply
  • Like
Likes vanhees71 and versine
Thread 'Why higher speeds need more power if backward force is the same?'

Thread 'Why higher speeds need more power if backward force is the same?'

Power = Force v Speed Power of my horse = 104kgx9.81m/s^2 x 0.732m/s = 1HP =746W Force/tension in rope stay the same if horse run at 0.73m/s or at 15m/s, so why then horse need to be more powerfull to pull at higher speed even if backward force at him(rope tension) stay the same? I understand that if I increase weight, it is hrader for horse to pull at higher speed because now is backward force increased, but don't understand why is harder to pull at higher speed if weight(backward force)...
View full post »

Similar threads

A Steady state confined flow field: Is it cyclic?
  • · Replies 9 ·
Replies
9
Views
2K
I Work - Energy Principle Application to Fluid Flow
  • · Replies 35 ·
2
Replies
35
Views
4K
I Work - Energy Principle Application to Fluid Flow
  • · Replies 48 ·
2
Replies
48
Views
5K
A Why are the Navier-Stokes equations inconsistent in this case?
  • · Replies 18 ·
Replies
18
Views
2K
A Conservation Laws from Continuity Equations in Fluid Flow
  • · Replies 2 ·
Replies
2
Views
2K
I Reference Frame, Difference in Kinetic Energy, Fuel Consumed
  • · Replies 19 ·
Replies
19
Views
2K
I Question about the velocity of the center of mass reference frame
  • · Replies 21 ·
Replies
21
Views
2K
B What Is Mass and How Is It Defined in Physics?
  • · Replies 23 ·
Replies
23
Views
2K
Doublet flow in Fluid Dynamics between two spheres or cylinders
  • · Replies 0 ·
Replies
0
Views
2K
I Laminar-turbulent transition and Reynolds number
  • · Replies 5 ·
Replies
5
Views
2K