# Thread: Bernoulli's principle

1. I have a doubt regarding Bernoulli's principle. It says the pressure of a static fluid is greater than the moving one.Can anybody tell me why?Because I feel like the moving fluid should have the more pressure.I know it is wrong.But how???? :?  2.

3. Bernoulli's is a conservation of energy equation for a fluid. so a given fluid has a certain amount of energy which is the same at any given time (its conserved). so for a given fluid, as it travels through whatever system you are analyzing, its energy will transfer between static pressure, kinetic energy and potential energy (of course there are also frictional and other losses to be considered if you are not assuming ideal conditions). so to answer your question, for a given fluid, if it is moving that means some of its energy that would be giving it larger static pressure is now going towards making it move thus it has lower static pressure ( I am of course assuming there is no change in height (potential energy) or any external non-conservative forces (like a pump) acting on the fluid). note that the kinetic energy term in the bernoulli equation is often called dynamic pressure so be sure when you are referring to pressure you are careful about this point.  4. Originally Posted by lance
Bernoulli's is a conservation of energy equation for a fluid. so a given fluid has a certain amount of energy which is the same at any given time (its conserved). so for a given fluid, as it travels through whatever system you are analyzing, its energy will transfer between static pressure, kinetic energy and potential energy (of course there are also frictional and other losses to be considered if you are not assuming ideal conditions). so to answer your question, for a given fluid, if it is moving that means some of its energy that would be giving it larger static pressure is now going towards making it move thus it has lower static pressure ( I am of course assuming there is no change in height (potential energy) or any external non-conservative forces (like a pump) acting on the fluid). note that the kinetic energy term in the bernoulli equation is often called dynamic pressure so be sure when you are referring to pressure you are careful about this point.
Lance,thanks for your reply.But without any external forces can a fluid flow?  5. :-D [i] 8) look at bernoulli's eqn.-------
[ P+dgh+1/2dv^2]=constant
P is pressure of fluid
d is density of fluid
v is velocityof fluid

for liquid flowing at reference level i.e.at ground level h=0;
hence eqn. reduces to [ P+1/2dv^2]=constant
here ----d is constant for a fluid;
SO, when v increaces
P decreases 8)

i think this will make u understand [/b]  6. yes...Thank you :-D Originally Posted by bittu
:-D [i] 8) look at bernoulli's eqn.-------
[ P+dgh+1/2dv^2]=constant
P is pressure of fluid
d is density of fluid
v is velocityof fluid

for liquid flowing at reference level i.e.at ground level h=0;
hence eqn. reduces to [ P+1/2dv^2]=constant
here ----d is constant for a fluid;
SO, when v increaces
P decreases 8)

i think this will make u understand [/b]  Bookmarks
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