| Topic: |
Science > Physics |
| User: |
"" |
| Date: |
26 Jun 2006 08:30:33 AM |
| Object: |
Understanding Bernoulli's Equation |
I am having trouble with pressure in a moving fluid. I understand the
pressure on the walls of a hose. And I understand how the pressure on
the walls of a hose will decrease as the fluid moves faster.
My problem is with the pressure IN the fluid. If I imagine a surface
perpendicular to the direction of flow, the water will be forcefully
pushing that surface. And that's an INCREASE in
pressure. A kite flies in moving air, but not in still air. Again an
increase in pressure with an increase in velocity.
I will be thankful to the person who can clear up my confusion on this
point!
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| User: "Dennis B" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 07:16:04 AM |
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wrote:
I am having trouble with pressure in a moving fluid. I understand the
pressure on the walls of a hose. And I understand how the pressure on
the walls of a hose will decrease as the fluid moves faster.
My problem is with the pressure IN the fluid. If I imagine a surface
perpendicular to the direction of flow, the water will be forcefully
pushing that surface. And that's an INCREASE in
pressure. A kite flies in moving air, but not in still air. Again an
increase in pressure with an increase in velocity.
I will be thankful to the person who can clear up my confusion on this
point!
Pressure does NOT decrease as the fluid velocity increases. You
intuitively know this to be false. Do not allow yourself to be
brainwashed by the cult of insane pseudo-science. The truth is to be
found in the medical community, which correctly explains fluid dynamics
through blood pressure. High blood pressure results from the
constriction or narrowing of blood vessels. When the circumference of
the vessels decreases, the velocity of the blood flow increases and the
pressure rises. Conversely, when the blood vessels dilate, the velocity
of the blood flow decreases and the blood pressure drops. Bernoulli
actually studied the relationship of blood pressure to the velocity of
blood. I'm not sure if he got the facts backwards or if his discoveries
have been corrupted.
-Dennis B
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| User: "tadchem" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 04:28:02 PM |
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Dennis B wrote:
Pressure does NOT decrease as the fluid velocity increases. You
intuitively know this to be false. Do not allow yourself to be
brainwashed by the cult of insane pseudo-science. The truth is to be
found in the medical community, which correctly explains fluid dynamics
through blood pressure. High blood pressure results from the
constriction or narrowing of blood vessels. When the circumference of
the vessels decreases, the velocity of the blood flow increases and the
pressure rises. Conversely, when the blood vessels dilate, the velocity
of the blood flow decreases and the blood pressure drops. Bernoulli
actually studied the relationship of blood pressure to the velocity of
blood. I'm not sure if he got the facts backwards or if his discoveries
have been corrupted.
Dennis, you have been tilting at a straw man.
From:
http://en.wikipedia.org/wiki/Bernoulli%27s_equation
"It is important to note that the only cause of the change in fluid
velocity is the difference in pressures either side of it. It is very
common for the Bernoulli effect to be quoted as if it states that a
change in velocity causes a change in pressure. The Bernoulli principle
does not make this statement and it is not the case."
If you are interested in what is really going on, you will read this
article and maybe even a few of the others to which it links, or
perhaps this will be informative:
http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html
If, however, you are simply filling your sails with the wind you might
take note of the fact that your boat is beached above the high-water
mark, so you aren't going to get anywhere.
Tom Davidson
Richmond, VA
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| User: "Dennis B" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 07:18:44 AM |
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wrote:
I am having trouble with pressure in a moving fluid. I understand the
pressure on the walls of a hose. And I understand how the pressure on
the walls of a hose will decrease as the fluid moves faster.
My problem is with the pressure IN the fluid. If I imagine a surface
perpendicular to the direction of flow, the water will be forcefully
pushing that surface. And that's an INCREASE in
pressure. A kite flies in moving air, but not in still air. Again an
increase in pressure with an increase in velocity.
I will be thankful to the person who can clear up my confusion on this
point!
Pressure does NOT decrease as the fluid velocity increases. You
intuitively know this to be false. Do not allow yourself to be
brainwashed by the cult of insane pseudo-science. The truth is to be
found in the medical community, which correctly explains fluid dynamics
through blood pressure. High blood pressure results from the
constriction or narrowing of blood vessels. When the circumference of
the vessels decreases, the velocity of the blood flow increases and the
pressure rises. Conversely, when the blood vessels dilate, the velocity
of the blood flow decreases and the blood pressure drops. Bernoulli
actually studied the relationship of blood pressure to the velocity of
blood. I'm not sure if he got the facts backwards or if his discoveries
have been corrupted.
-Dennis B
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| User: "Dennis B" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 07:19:21 AM |
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wrote:
I am having trouble with pressure in a moving fluid. I understand the
pressure on the walls of a hose. And I understand how the pressure on
the walls of a hose will decrease as the fluid moves faster.
My problem is with the pressure IN the fluid. If I imagine a surface
perpendicular to the direction of flow, the water will be forcefully
pushing that surface. And that's an INCREASE in
pressure. A kite flies in moving air, but not in still air. Again an
increase in pressure with an increase in velocity.
I will be thankful to the person who can clear up my confusion on this
point!
Pressure does NOT decrease as the fluid velocity increases. You
intuitively know this to be false. Do not allow yourself to be
brainwashed by the cult of insane pseudo-science. The truth is to be
found in the medical community, which correctly explains fluid dynamics
through blood pressure. High blood pressure results from the
constriction or narrowing of blood vessels. When the circumference of
the vessels decreases, the velocity of the blood flow increases and the
pressure rises. Conversely, when the blood vessels dilate, the velocity
of the blood flow decreases and the blood pressure drops. Bernoulli
actually studied the relationship of blood pressure to the velocity of
blood. I'm not sure if he got the facts backwards or if his discoveries
have been corrupted.
-Dennis B
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| User: "PD" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 07:42:54 AM |
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Dennis B wrote:
actionintegral@yahoo.com wrote:
I am having trouble with pressure in a moving fluid. I understand the
pressure on the walls of a hose. And I understand how the pressure on
the walls of a hose will decrease as the fluid moves faster.
My problem is with the pressure IN the fluid. If I imagine a surface
perpendicular to the direction of flow, the water will be forcefully
pushing that surface. And that's an INCREASE in
pressure. A kite flies in moving air, but not in still air. Again an
increase in pressure with an increase in velocity.
I will be thankful to the person who can clear up my confusion on this
point!
Pressure does NOT decrease as the fluid velocity increases. You
intuitively know this to be false. Do not allow yourself to be
brainwashed by the cult of insane pseudo-science. The truth is to be
found in the medical community, which correctly explains fluid dynamics
through blood pressure. High blood pressure results from the
constriction or narrowing of blood vessels. When the circumference of
the vessels decreases, the velocity of the blood flow increases and the
pressure rises. Conversely, when the blood vessels dilate, the velocity
of the blood flow decreases and the blood pressure drops. Bernoulli
actually studied the relationship of blood pressure to the velocity of
blood. I'm not sure if he got the facts backwards or if his discoveries
have been corrupted.
-Dennis B
Repeating your confusion three times does not make your point more
forceful.
High blood pressure refers to a difference between systolic and
diastolic pressures, and this is primarily due to the *viscosity* of
blood being pushed through a set of constricted vessels. Viscous
effects have nothing to do with Bernoulli's principle.
Misapplication of ideas to further your mistakes about Bernoulli's
principle does not help your cause against the "cult of insane
pseudo-science". In fact, you appear to be wearing the wrong coat of
arms in that battle.
PD
PD
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| User: "Dennis B" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 11:57:14 AM |
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PD wrote:
Dennis B wrote:
actionintegral@yahoo.com wrote:
I am having trouble with pressure in a moving fluid. I understand the
pressure on the walls of a hose. And I understand how the pressure on
the walls of a hose will decrease as the fluid moves faster.
My problem is with the pressure IN the fluid. If I imagine a surface
perpendicular to the direction of flow, the water will be forcefully
pushing that surface. And that's an INCREASE in
pressure. A kite flies in moving air, but not in still air. Again an
increase in pressure with an increase in velocity.
I will be thankful to the person who can clear up my confusion on this
point!
Pressure does NOT decrease as the fluid velocity increases. You
intuitively know this to be false. Do not allow yourself to be
brainwashed by the cult of insane pseudo-science. The truth is to be
found in the medical community, which correctly explains fluid dynamics
through blood pressure. High blood pressure results from the
constriction or narrowing of blood vessels. When the circumference of
the vessels decreases, the velocity of the blood flow increases and the
pressure rises. Conversely, when the blood vessels dilate, the velocity
of the blood flow decreases and the blood pressure drops. Bernoulli
actually studied the relationship of blood pressure to the velocity of
blood. I'm not sure if he got the facts backwards or if his discoveries
have been corrupted.
-Dennis B
Repeating your confusion three times does not make your point more
forceful.
High blood pressure refers to a difference between systolic and
diastolic pressures, and this is primarily due to the *viscosity* of
blood being pushed through a set of constricted vessels. Viscous
effects have nothing to do with Bernoulli's principle.
Misapplication of ideas to further your mistakes about Bernoulli's
principle does not help your cause against the "cult of insane
pseudo-science". In fact, you appear to be wearing the wrong coat of
arms in that battle.
PD
PD
First of all, when Bernoulli studied the relationship between blood
pressure and the velocity of blood, he didn't cut off the circulation
(like they do today in order to measure the difference between systolic
and diastolic pressure). Rather he simply stuck a glass tube into an
unimpeded vessel. The extent to which the blood flowed up the tube
revealed the pressure. The results of such a test would be related to
the angle of the tube. If the tube was angled such that the opening was
directed into the flow, the blood would flow up the tube further than
if the opening were were oriented away from the blood flow. This
elucidates the difference between ram pressure and static pressure.
Nevertheless, blood will flow further up the tube in any direction when
the blood vessels are constricted than it will when the blood vessels
are dilated. This is because total pressure goes up as the vessels
constrict. There is a fixed amount of fluid within the circulatory
system. If the container of the circulatory system decreases in volume
while the volume of fluid remains the same, then the pressure goes up.
To use an analogy, it is just like squeezing a balloon. As the blood
vessels constrict, thus reducing the circumference of the blood
vessels, the velocity of the blood increases and the blood pressure
goes up. One may be inclined to argue that Bernoulli's equations apply
only if the total pressure remains constant. As I understand, the
reason for such an argument would be based upon the presumption that an
increase of pressure would involve an increase in the volume of fluid
which flows past a point of reference per unit of time (such as per
minute). Yet, although the blood flows through constricted vessels at a
greater velocity and pressure than through dilated vessels, the same
volume of fluid passes through the constricted vessels per unit of time
[i.e., per minute] as through dilated vessels, presuming the heart
continues to pump the same volume of fluid per unit of time [i.e. per
minute])...Thus, proving that the increase of pressure is due solely to
the increase of velocity as a result of the blood vessel constriction,
which is analogous to an increase of velocity due to a decrease of
tubing diameter.
Futhermore, ram pressure and static pressure are actually related. Ram
pressure is merely a manifestation of unrestrained static pressure. For
example, what is the difference between ram pressure and static
pressure in air leaking from a tank of compressed air? Obviously, there
is no real difference. It is merely a matter of whether the pressurised
fluid is restrained (by an external pressure) or not. If not, the fluid
flows and we call it ram pressure (or kinetic energy, because the
kinetic energy of the unrestrained molecules [or particles] is
distributed in the direction of motion). If the fluid is restrained
then we call it static pressure (or potential energy, because the
kinetic energy of the intrinsic molecular vibration is distributed
equally in all directions).
Ultimately, the fact is that particles continue to collide with the
surface of a body, even the surface is parallel to the axis of
(relative) motion (such as the inner walls of blood vessels),
regardless of velocity or any possible constrained motion. And the
particles collide into the surface with greater force as velocity
increases. This is what causes friction and explains why friction
increases as velocity increases. Although the force of collision may be
oriented primarily in the direction of flow (as opposed to being
distributed equally in all directions)...the force of such collisions
still exert an outward force on the inside surface of the fluid
channel. Total (scalar) pressure remains constant since momentum is
conserved, because any increase of force in the direction of motion is
counterbalanced by an equivalent decrease of force opposite the
direction of motion.
-Dennis B
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| User: "" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 10:30:43 AM |
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Dennis B wrote:
Pressure does NOT decrease as the fluid velocity increases.
You are confusing pressure measured parallel to the direction of motion
with pressure measured transverse to the direction of motion. Like I
was before I asked the question.
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| User: "Dennis B" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 12:07:31 PM |
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wrote:
Dennis B wrote:
Pressure does NOT decrease as the fluid velocity increases.
You are confusing pressure measured parallel to the direction of motion
with pressure measured transverse to the direction of motion. Like I
was before I asked the question.
Actually, I'm not. Read my last post. It thoroughly explains why force
increases both parallel and perpendicular to the direction of motion as
velocity increases. To summarise, in the case of fluid flowing through
a tube, it is because particles continue to collide with the inner
walls of the tubing regardless of velocity...the greater the velocity
the greater the force of collision and therefore the greater the
outward pressure. Although I question whether force increases perfectly
perpendicular to the direction of motion, there is definitely an
increase of force between the two axis as velocity increases.
-Dennis B
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| User: "" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 02:44:57 PM |
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it is because particles continue to collide with the inner
walls of the tubing regardless of velocity...the greater the velocity
the greater the force of collision and therefore the greater the
outward pressure. Although I question whether force increases perfectly
perpendicular to the direction of motion, there is definitely an
increase of force between the two axis as velocity increases.
The context of the notion that "pressure decreases as velocity
increases" is understood to be idealized. It is easy to imagine that a
viscosity in the fluid will cause a "bulging" in the hose or vein and a
resultant increase in the pressure perpendicular to the net direction
of flow.
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| User: "Dennis B" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 10:18:08 PM |
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wrote:
it is because particles continue to collide with the inner
walls of the tubing regardless of velocity...the greater the velocity
the greater the force of collision and therefore the greater the
outward pressure. Although I question whether force increases perfectly
perpendicular to the direction of motion, there is definitely an
increase of force between the two axis as velocity increases.
The context of the notion that "pressure decreases as velocity
increases" is understood to be idealized. It is easy to imagine that a
viscosity in the fluid will cause a "bulging" in the hose or vein and a
resultant increase in the pressure perpendicular to the net direction
of flow.
Yes! Precisely. The Bernoulli principle equation applies only to
frictionless non-viscous fluids and is therefore a myth (with a seed of
truth in it, due to the very real existence of frictionless inviscid
super-fluids).
Furthermore, as I said previously, there is no real distinction between
ram pressure and static pressure. Ram pressure is merely an
"unbalanced" static pressure, whereas static pressure is balanced,
since the forces of all the molecular vibrations are distributed
equally in all directions. It may appear that there is a difference
because one would expect that the energy of a fluid's velocity to be
independent of it's static pressure. For example, one could pulse the
pressure so as to create oscillating ram pressures. Yet, the
oscillating ram pressures are created from oscillating static
pressures. And in order to measure "ram pressure", one must obstruct
the flow so as to convert the ram pressure into "static pressure".
Thus, what you are measuring is actually static pressure and not "ram
pressure"!
-Dennis B
Beware the cult of insane pseudo-science!
Destroy the cult of insane pseudoscience!
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| User: "Dennis B" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 10:51:11 PM |
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Dennis B wrote:
actionintegral@yahoo.com wrote:
it is because particles continue to collide with the inner
walls of the tubing regardless of velocity...the greater the velocity
the greater the force of collision and therefore the greater the
outward pressure. Although I question whether force increases perfectly
perpendicular to the direction of motion, there is definitely an
increase of force between the two axis as velocity increases.
The context of the notion that "pressure decreases as velocity
increases" is understood to be idealized. It is easy to imagine that a
viscosity in the fluid will cause a "bulging" in the hose or vein and a
resultant increase in the pressure perpendicular to the net direction
of flow.
Yes! Precisely. The Bernoulli principle equation applies only to
frictionless non-viscous fluids and is therefore a myth (with a seed of
truth in it, due to the very real existence of frictionless inviscid
super-fluids).
Furthermore, as I said previously, there is no real distinction between
ram pressure and static pressure. Ram pressure is merely an
"unbalanced" static pressure, whereas static pressure is balanced,
since the forces of all the molecular vibrations are distributed
equally in all directions. It may appear that there is a difference
because one would expect that the energy of a fluid's velocity to be
independent of it's static pressure. For example, one could pulse the
pressure so as to create oscillating ram pressures. Yet, the
oscillating ram pressures are created from oscillating static
pressures. And in order to measure "ram pressure", one must obstruct
the flow so as to convert the ram pressure into "static pressure".
Thus, what you are measuring is actually static pressure and not "ram
pressure"!
-Dennis B
Beware the cult of insane pseudo-science!
Destroy the cult of insane pseudoscience!
To simplify:
As I said previously, there is no real distinction between ram pressure
and static pressure. Ram pressure is merely an "unbalanced" static
pressure (whereas static pressure is balanced, since the forces of all
the molecular vibrations are distributed equally in all directions).
It may appear that there is a difference between static pressure and
ram because one would expect the energy of a fluid's velocity to be
independent of it's static pressure. For example, one could apply an
external force so as to increase ram pressure. Yet, the ram pressure is
created from an increased, yet unrestrained, static pressure. This fact
is made evident by measuring the ram pressure: In order to measure "ram
pressure", one must obstruct the flow so as to convert the ram pressure
into "static pressure". Thus, what you are measuring is actually static
pressure and not "ram pressure"!
-Dennis B
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| User: "Dennis B" |
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| Title: Re: Understanding Bernoulli's Equation |
29 Jun 2006 11:31:20 PM |
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Dennis B wrote:
Dennis B wrote:
actionintegral@yahoo.com wrote:
it is because particles continue to collide with the inner
walls of the tubing regardless of velocity...the greater the velocity
the greater the force of collision and therefore the greater the
outward pressure. Although I question whether force increases perfectly
perpendicular to the direction of motion, there is definitely an
increase of force between the two axis as velocity increases.
The context of the notion that "pressure decreases as velocity
increases" is understood to be idealized. It is easy to imagine that a
viscosity in the fluid will cause a "bulging" in the hose or vein and a
resultant increase in the pressure perpendicular to the net direction
of flow.
Yes! Precisely. The Bernoulli principle equation applies only to
frictionless non-viscous fluids and is therefore a myth (with a seed of
truth in it, due to the very real existence of frictionless inviscid
super-fluids).
Furthermore, as I said previously, there is no real distinction between
ram pressure and static pressure. Ram pressure is merely an
"unbalanced" static pressure, whereas static pressure is balanced,
since the forces of all the molecular vibrations are distributed
equally in all directions. It may appear that there is a difference
because one would expect that the energy of a fluid's velocity to be
independent of it's static pressure. For example, one could pulse the
pressure so as to create oscillating ram pressures. Yet, the
oscillating ram pressures are created from oscillating static
pressures. And in order to measure "ram pressure", one must obstruct
the flow so as to convert the ram pressure into "static pressure".
Thus, what you are measuring is actually static pressure and not "ram
pressure"!
-Dennis B
Beware the cult of insane pseudo-science!
Destroy the cult of insane pseudoscience!
To simplify:
As I said previously, there is no real distinction between ram pressure
and static pressure. Ram pressure is merely an "unbalanced" static
pressure (whereas static pressure is balanced, since the forces of all
the molecular vibrations are distributed equally in all directions).
It may appear that there is a difference between static pressure and
ram because one would expect the energy of a fluid's velocity to be
independent of it's static pressure. For example, one could apply an
external force so as to increase ram pressure. Yet, the ram pressure is
created from an increased, yet unrestrained, static pressure. This fact
is made evident by measuring the ram pressure: In order to measure "ram
pressure", one must obstruct the flow so as to convert the ram pressure
into "static pressure". Thus, what you are measuring is actually static
pressure and not "ram pressure"!
-Dennis B
To elaborate:
The ram pressure of blood flow created by the heart is due to a
localised increase in the energy of the static pressure created by the
constriction of vessels (in the case of high blood pressure, for
example). When determining ram pressure, one is actually measuring the
sum of the energy added (such as by the pulsing of the heart) to the
intrinsic energy of static pressure due to constriction of the vessels.
In order to measure the ram pressure, it must be fully obstructed in
order to transfer it's force, which then converts it into static
pressure. Imagine if the heart were to clench and not relax. This would
cause a localised increase in pressure, which if unrestrained, would
flow in the form of ram pressure throughout the circulatory system as a
pulse of increased pressure. Yet, the energy of the pulse would
eventually be dissipated throughout the circuluatory system which,
being a closed system, ultimately restrains the increase of pressure
created by the heart. When the energy is dissipated equally throughout
the circulatory system, it then contributes to the static pressure of
the entire circulatory system. The heart therefore like a hand
squeezing a balloon, whereas the ciculatory system is akin to the
ballon. Ram pressure can therfore be defined as an imbalance of static
pressure in a fluid.
-Dennis B
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| User: "Phineas T Puddleduck" |
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| Title: Re: Understanding Bernoulli's Equation |
26 Jun 2006 08:40:42 AM |
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In article <1151328633.327475.108410@b68g2000cwa.googlegroups.com>,
<actionintegral@yahoo.com> wrote:
I am having trouble with pressure in a moving fluid. I understand the
pressure on the walls of a hose. And I understand how the pressure on
the walls of a hose will decrease as the fluid moves faster.
My problem is with the pressure IN the fluid. If I imagine a surface
perpendicular to the direction of flow, the water will be forcefully
pushing that surface. And that's an INCREASE in
pressure. A kite flies in moving air, but not in still air. Again an
increase in pressure with an increase in velocity.
I will be thankful to the person who can clear up my confusion on this
point!
Are you perhaps confusing ram pressure with static pressure?
http://en.wikipedia.org/wiki/Ram_pressure
http://en.wikipedia.org/wiki/Static_pressure
I believe that's the source of confusion.
--
The greatest enemy of science is pseudoscience.
Jaffa cakes. Sweet delicious orangey jaffa goodness, and an abject lesson why
parroting information from the web will not teach you cosmology.
Official emperor of sci.physics, head mumbler of the "Cult of INSANE SCIENCE".
Please pay no attention to my butt poking forward, it is expanding.
Relf's Law?
"***** repeated to the limit of infinity asymptotically approaches
the odour of roses."
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| User: "" |
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| Title: Re: Understanding Bernoulli's Equation |
26 Jun 2006 08:50:20 AM |
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Phineas T Puddleduck wrote:
Are you perhaps confusing ram pressure with static pressure?
Yes, I was! Thank you very much.
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| User: "Phineas T Puddleduck" |
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| Title: Re: Understanding Bernoulli's Equation |
26 Jun 2006 08:53:14 AM |
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In article <1151329820.802283.226150@b68g2000cwa.googlegroups.com>,
<actionintegral@yahoo.com> wrote:
Phineas T Puddleduck wrote:
Are you perhaps confusing ram pressure with static pressure?
Yes, I was! Thank you very much.
No problem. The distinction seems subtle, and not well explained in
some resources ;-) Once you think of it in the two cases (1) static
w.r.t the fluid and (2) moving w.r.t. the fluid - you can begin to see
why this is the case. The one website has a nice java application that
shows it graphically.
--
The greatest enemy of science is pseudoscience.
Jaffa cakes. Sweet delicious orangey jaffa goodness, and an abject lesson why
parroting information from the web will not teach you cosmology.
Official emperor of sci.physics, head mumbler of the "Cult of INSANE SCIENCE".
Please pay no attention to my butt poking forward, it is expanding.
Relf's Law?
"***** repeated to the limit of infinity asymptotically approaches
the odour of roses."
.
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| User: "Phineas T Puddleduck" |
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| Title: Re: Understanding Bernoulli's Equation |
26 Jun 2006 08:42:55 AM |
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In article <1151328633.327475.108410@b68g2000cwa.googlegroups.com>,
<actionintegral@yahoo.com> wrote:
I am having trouble with pressure in a moving fluid. I understand the
pressure on the walls of a hose. And I understand how the pressure on
the walls of a hose will decrease as the fluid moves faster.
My problem is with the pressure IN the fluid. If I imagine a surface
perpendicular to the direction of flow, the water will be forcefully
pushing that surface. And that's an INCREASE in
pressure. A kite flies in moving air, but not in still air. Again an
increase in pressure with an increase in velocity.
I will be thankful to the person who can clear up my confusion on this
point!
I think you are confusing Ra, with Static...
This help?
http://home.earthlink.net/~mmc1919/venturi_discuss_nomath.html
"Ram Pressure and Static Pressure
The demo and the other sections in this web page refer to the pressure.
More specifically, they are referring to static pressure, which is the
pressure felt by an object or person suspended in the fluid and moving
with it. This pressure is static because the suspended object or person
is not moving relative to the fluid. In this section only we will
discuss another other type of pressure: ram pressure.
Static pressure should not be confused with ram pressure, which is the
pressure felt by an object because it is moving relative to the fluid.
Basically, the fluid is ramming into the moving object, or vice versa.
The ram pressure increases when the speed increases. This explains the
stronger force felt by your hand when it is held a fast moving current.
In the faster current, your hand is deflecting more flowing fluid from
its original path.
As you wade across a rushing stream, the force against your legs is
from the ram pressure, and it is directed downstream.
The static pressure decreases when the speed increases, as explained in
the Background Theory section above. This explains why the water stream
coming out of a firefighter's hose gets narrower a short distance past
the nozzle - the stronger atmospheric pressure overwhelms the weaker
static pressure in the quickly flowing water and compresses the water
stream.
At the bottom of a swimming pool, the force on your body is from the
static pressure of the water, and it is directed inwards.
During the moving part of the jostling demo above, static pressure
would correspond to the jostling felt by a teacher running along in the
center of the children. That pressure would be slight. Ram pressure
would correspond to the body blows experienced by an unsuspecting
teacher standing in the path of the oncoming crowd (big ouch!)."
--
The greatest enemy of science is pseudoscience.
Jaffa cakes. Sweet delicious orangey jaffa goodness, and an abject lesson why
parroting information from the web will not teach you cosmology.
Official emperor of sci.physics, head mumbler of the "Cult of INSANE SCIENCE".
Please pay no attention to my butt poking forward, it is expanding.
Relf's Law?
"***** repeated to the limit of infinity asymptotically approaches
the odour of roses."
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