- #1
seratia
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From reading textbooks, we just know that there is a pressure difference because the fluid speeds up. But WHY is there a pressure difference, why does the pressure decrease?
Why does the pressure change at the narrowing of a tube
In summary, Bernoulli's principle states that the pressure in an artery is constant, regardless of the flow of blood.
- #2
russ_watters
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Welcome to PF!
Though it isn't always a popular view, I think it is easiest to understand the issue by recognizing that pressure doesn't change in a constriction, but rather only shifts between different types of pressure (static and dynamic/velocity pressure).
The opposing school of thought holds that "pressure" only refers to static pressure and velocity pressure isn't really pressure, but is kinetic energy per unit volume (which still has units of pressure). In this way you can say that "pressure" is converted to something like motion.
In either case, it is important to recognise that this situation (Bernoulli's principle) is a conservation of energy statement. The conversion maintains a constant total system energy.
Though it isn't always a popular view, I think it is easiest to understand the issue by recognizing that pressure doesn't change in a constriction, but rather only shifts between different types of pressure (static and dynamic/velocity pressure).
The opposing school of thought holds that "pressure" only refers to static pressure and velocity pressure isn't really pressure, but is kinetic energy per unit volume (which still has units of pressure). In this way you can say that "pressure" is converted to something like motion.
In either case, it is important to recognise that this situation (Bernoulli's principle) is a conservation of energy statement. The conversion maintains a constant total system energy.
- #3
seratia
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Hi, thank you for the welcome.
Actually, I am in the medical field. The concept of blood pressure does not make sense tome at all. When I talk to other students about it they look at me like I am crazy. But honestly, "blood pressure" REALLY doesn't make sense. There are so many questions that I can ask about it.
I just decided to read physics textbooks and work my way from the ground up.
As a medical professional, I feel uncomfortable discussing blood pressure with patients when I don't fully understand it myself.
Actually, I am in the medical field. The concept of blood pressure does not make sense tome at all. When I talk to other students about it they look at me like I am crazy. But honestly, "blood pressure" REALLY doesn't make sense. There are so many questions that I can ask about it.
I just decided to read physics textbooks and work my way from the ground up.
As a medical professional, I feel uncomfortable discussing blood pressure with patients when I don't fully understand it myself.
- #4
russ_watters
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We actually get blood pressure questions a lot. One thing to remember about how Bernoulli's principle applies to blood pressure is that Bernoulli's principle applies to only one flow situation at a time, along a streamline. So, for example, if your vessels dilate, your system has been changed and you can't compare it to the previous condition via Bernoulli's.
- #5
sophiecentaur
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I can sympathise with that because Physics often seems to present descriptions 'the wrong way round' for the uninitiated. You worry about the word "pressure", but the word "gradient" needs to be added in order to account for the flow. Firstly, you know that you can 'feel' the pressure in an artery because it pushes against your finger and the pressurised air in the 'cuff' can stop the flow. Some pressure gradient is needed all the way round the circuit to move the blood in the right direction all the way round and back into the Atria. In a single tube circuit with a uniform diameter tube, the pressure would drop steadily, being highest on the way out of the heart and lowest inside the Atria. In a real body, the capillaries account for a lot of the pressure drop and you can't easily get a useful measure of the veinous pressure (it's different for different heights in the body. Experience (I guess) has shown that the pressure on the way into the pump is low enough not to affect things and that the 'excess' pressure in the arteries gives a good enough idea of the pressure drop across the capilliaries.seratia said:
So. your measurement of 'Pressure' near to the elbow is near enough to the 'Pressure Difference' around the circuit. Makes sense?
Related to Why does the pressure change at the narrowing of a tube
1. Why does pressure increase at the narrowing of a tube?
Pressure increases at the narrowing of a tube because the same amount of fluid is moving through a smaller area, resulting in a higher force per unit area.
2. What causes the pressure to decrease at the narrowing of a tube?
The pressure decreases at the narrowing of a tube because the same amount of fluid is now spread out over a larger area, resulting in a lower force per unit area.
3. Why is there a change in pressure at the narrowing of a tube?
The change in pressure at the narrowing of a tube is due to the Bernoulli's principle, which states that as the speed of a fluid increases, its pressure decreases.
4. How does the shape of the tube affect the pressure change at the narrowing?
The shape of the tube can affect the pressure change at the narrowing because it can alter the flow of the fluid and potentially cause more or less resistance, resulting in a different pressure change.
5. Can the pressure change at the narrowing of a tube be manipulated?
Yes, the pressure change at the narrowing of a tube can be manipulated by adjusting the shape, size, and fluid flow through the tube. This is often used in engineering and design to control the pressure and flow of fluids in various systems.
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