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Systolic pressure

Systolic pressure is the maximum blood pressure.

Diastolic pressure

Diastolic pressure is the minimum blood pressure.

U.S. Army Spc. Monica Brown takes a soldier's blood pressure reading at the hospital on Forward Operating Base Salerno, Afghanistan, March 10, 2008.
In routine blood pressure measurements, an inflatable cuff is placed on the upper arm at the same level as the heart. Blood flow is detected just below the cuff, and corresponding pressures are transmitted to a mercury-filled manometer. (credit: U.S. Army photo by Spc. Micah E. Clare\4TH BCT)

Calculating height of iv bag: blood pressure and intravenous infusions

Intravenous infusions are usually made with the help of the gravitational force. Assuming that the density of the fluid being administered is 1.00 g/ml, at what height should the IV bag be placed above the entry point so that the fluid just enters the vein if the blood pressure in the vein is 18 mm Hg above atmospheric pressure? Assume that the IV bag is collapsible.

Strategy for (a)

For the fluid to just enter the vein, its pressure at entry must exceed the blood pressure in the vein (18 mm Hg above atmospheric pressure). We therefore need to find the height of fluid that corresponds to this gauge pressure.


We first need to convert the pressure into SI units. Since 1.0 mm Hg = 133 Pa ,

P = 18 mm Hg × 133 Pa 1.0 mm Hg = 2400 Pa . size 12{P="18"`"mm"`"Hg" times { {"133"`"Pa"} over {1 "." 0`"mm"`"Hg"} } ="2400"`"Pa" "." } {}

Rearranging P g = hρg size 12{P rSub { size 8{g} } =hρg} {} for h size 12{h} {} gives h = P g ρg size 12{h= { {P rSub { size 8{g} } } over {ρg} } } {} . Substituting known values into this equation gives

h = 2400 N /m 2 1 . 0 × 10 3 kg/m 3 9 . 80 m/s 2 = 0.24 m. alignl { stack { size 12{h= { {"2400"`"N/m" rSup { size 8{2} } } over { left (1 "." 0 times "10" rSup { size 8{3} } `"kg/m" rSup { size 8{3} } right ) left (9 "." "80"`"m/s" rSup { size 8{2} } right )} } } {} #" "=" 0" "." "24"`m "." {} } } {}


The IV bag must be placed at 0.24 m above the entry point into the arm for the fluid to just enter the arm. Generally, IV bags are placed higher than this. You may have noticed that the bags used for blood collection are placed below the donor to allow blood to flow easily from the arm to the bag, which is the opposite direction of flow than required in the example presented here.

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A barometer is a device that measures atmospheric pressure. A mercury barometer is shown in [link] . This device measures atmospheric pressure, rather than gauge pressure, because there is a nearly pure vacuum above the mercury in the tube. The height of the mercury is such that hρg = P atm size 12{hρg=P rSub { size 8{"atm"} } } {} . When atmospheric pressure varies, the mercury rises or falls, giving important clues to weather forecasters. The barometer can also be used as an altimeter, since average atmospheric pressure varies with altitude. Mercury barometers and manometers are so common that units of mm Hg are often quoted for atmospheric pressure and blood pressures. [link] gives conversion factors for some of the more commonly used units of pressure.

Mercury barometer has an evacuated glass tube inverted and placed in the mercury container. The height of the mercury column in the inverted tube is determined by the atmospheric pressure.
A mercury barometer measures atmospheric pressure. The pressure due to the mercury’s weight, hρg size 12{hρg} {} , equals atmospheric pressure. The atmosphere is able to force mercury in the tube to a height h size 12{h} {} because the pressure above the mercury is zero.
Conversion factors for various pressure units
Conversion to N/m 2 (Pa) Conversion from atm
1.0 atm = 1 . 013 × 10 5 N/m 2 size 12{1 "." 0`"atm"=1 "." "013" times "10" rSup { size 8{5} } `"N/m" rSup { size 8{2} } } {} 1.0 atm = 1 . 013 × 10 5 N/m 2 size 12{1 "." 0`"atm"=1 "." "013" times "10" rSup { size 8{5} } `"N/m" rSup { size 8{2} } } {}
1.0 dyne/cm 2 = 0 . 10 N/m 2 size 12{1 "." 0`"dyne/cm" rSup { size 8{2} } =0 "." "10"`"N/m" rSup { size 8{2} } } {} 1 . 0 atm = 1 . 013 × 10 6 dyne/cm 2 size 12{1 "." 0`"atm"=1 "." "013" times "10" rSup { size 8{6} } `"dyne/cm" rSup { size 8{2} } } {}
1 . 0 kg/cm 2 = 9 . 8 × 10 4 N/m 2 size 12{1 "." 0`"kg/cm" rSup { size 8{2} } =9 "." 8 times "10" rSup { size 8{4} } `"N/m" rSup { size 8{2} } } {} 1 . 0 atm = 1 . 013 kg/cm 2 size 12{1 "." 0`"atm"=1 "." "013"`"kg/cm" rSup { size 8{2} } } {}
1 . 0 lb/in . 2 = 6 . 90 × 10 3 N/m 2 size 12{1 "." 0`"lb/in" "." rSup { size 8{2} } =6 "." "90" times "10" rSup { size 8{3} } `"N/m" rSup { size 8{2} } } {} 1 . 0 atm = 14 . 7 lb/in . 2 size 12{1 "." 0`"atm"="14" "." 7`"lb/in" "." rSup { size 8{2} } } {}
1.0 mm Hg = 133 N/m 2 size 12{1 "." 0`"mm"`"Hg"="133"`"N/m" rSup { size 8{2} } } {} 1 . 0 atm = 760 mm Hg size 12{1 "." 0`"atm"="760"`"mm"`"Hg"} {}
1 . 0 cm Hg = 1 . 33 × 10 3 N/m 2 size 12{1 "." 0`"cm"`"Hg"=1 "." "33" times "10" rSup { size 8{3} } `"N/m" rSup { size 8{2} } } {} 1 . 0 atm = 76 . 0 cm Hg size 12{1 "." 0`"atm"="76" "." 0`"cm"`"Hg"} {}
1 . 0 cm water = 98 . 1 N/m 2 size 12{1 "." 0`"cm"`"water"="98" "." 1`"N/m" rSup { size 8{2} } } {} 1 . 0 atm = 1 . 03 × 10 3 cm water size 12{1 "." 0`"atm"=1 "." "03" times "10" rSup { size 8{3} } `"cm"`"water"} {}
1.0 bar = 1 . 000 × 10 5 N/m 2 size 12{1 "." 0`"bar"=1 "." "000" times "10" rSup { size 8{5} } `"N/m" rSup { size 8{2} } } {} 1 . 0 atm = 1.013 bar size 12{1 "." 0`"atm"=1 "." "013"`"bar"} {}
1.0 millibar = 1 . 000 × 10 2 N/m 2 size 12{1 "." 0`"millibar"=1 "." "000" times "10" rSup { size 8{2} } `"N/m" rSup { size 8{2} } } {} 1.0 atm = 1013 millibar

Section summary

  • Gauge pressure is the pressure relative to atmospheric pressure.
  • Absolute pressure is the sum of gauge pressure and atmospheric pressure.
  • Aneroid gauge measures pressure using a bellows-and-spring arrangement connected to the pointer of a calibrated scale.
  • Open-tube manometers have U-shaped tubes and one end is always open. It is used to measure pressure.
  • A mercury barometer is a device that measures atmospheric pressure.

Conceptual questions

Explain why the fluid reaches equal levels on either side of a manometer if both sides are open to the atmosphere, even if the tubes are of different diameters.

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[link] shows how a common measurement of arterial blood pressure is made. Is there any effect on the measured pressure if the manometer is lowered? What is the effect of raising the arm above the shoulder? What is the effect of placing the cuff on the upper leg with the person standing? Explain your answers in terms of pressure created by the weight of a fluid.

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Considering the magnitude of typical arterial blood pressures, why are mercury rather than water manometers used for these measurements?

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Find the gauge and absolute pressures in the balloon and peanut jar shown in [link] , assuming the manometer connected to the balloon uses water whereas the manometer connected to the jar contains mercury. Express in units of centimeters of water for the balloon and millimeters of mercury for the jar, taking h = 0 . 0500 m size 12{h=0 "." "0500"`m} {} for each.


P g = 5.00 cm H 2 O, P abs = 1.035 × 10 3 cm H 2 O. alignl { stack { size 12{P rSub { size 8{g} } =5 "." "00"`"cm"`H rSub { size 8{2} } "O,"} {} #P rSub { size 8{"abs"} } =1 "." "035" times "10" rSup { size 8{3} } `"cm"`H rSub { size 8{2} } O "." {} } } {}


P g = 50.0 mm Hg , P abs = 710 mm Hg. alignl { stack { size 12{P rSub { size 8{g} } = - "50" "." 0`"mm"`"Hg,"} {} #P rSub { size 8{"abs"} } ="710"`"mm"`"Hg" "." {} } } {}

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(a) Convert normal blood pressure readings of 120 over 80 mm Hg to newtons per meter squared using the relationship for pressure due to the weight of a fluid ( P = hρg ) size 12{ \( P=hρg \) } {} rather than a conversion factor. (b) Discuss why blood pressures for an infant could be smaller than those for an adult. Specifically, consider the smaller height to which blood must be pumped.

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How tall must a water-filled manometer be to measure blood pressures as high as 300 mm Hg?

4.08 m

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Pressure cookers have been around for more than 300 years, although their use has strongly declined in recent years (early models had a nasty habit of exploding). How much force must the latches holding the lid onto a pressure cooker be able to withstand if the circular lid is 25.0 cm size 12{"25" "." 0`"cm"} {} in diameter and the gauge pressure inside is 300 atm? Neglect the weight of the lid.

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Suppose you measure a standing person’s blood pressure by placing the cuff on his leg 0.500 m below the heart. Calculate the pressure you would observe (in units of mm Hg) if the pressure at the heart were 120 over 80 mm Hg. Assume that there is no loss of pressure due to resistance in the circulatory system (a reasonable assumption, since major arteries are large).

Δ P = 38.7 mm Hg, Leg blood pressure = 159 119 . alignl { stack { size 12{ΔP="38" "." 7`"mm"`"Hg,"} {} #size 12{"Leg"`"blood"`"pressure"= { {"159"} over {"119"} } "." } {} } } {}

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A submarine is stranded on the bottom of the ocean with its hatch 25.0 m below the surface. Calculate the force needed to open the hatch from the inside, given it is circular and 0.450 m in diameter. Air pressure inside the submarine is 1.00 atm.

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Assuming bicycle tires are perfectly flexible and support the weight of bicycle and rider by pressure alone, calculate the total area of the tires in contact with the ground. The bicycle plus rider has a mass of 80.0 kg, and the gauge pressure in the tires is 3 . 50 × 10 5 Pa size 12{3 "." "50" times "10" rSup { size 8{5} } `"Pa"} {} .

22 . 4 cm 2 size 12{"22" "." 4`"cm" rSup { size 8{2} } } {}

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Questions & Answers

how does sound affect temperature
Clement Reply
sound is directly proportional to the temperature.
how to solve wave question
Wisdom Reply
I would like to know how I am not at all smart when it comes to math. please explain so I can understand. sincerly
Just know d relationship btw 1)wave length 2)frequency and velocity
First of all, you are smart and you will get it👍🏽... v = f × wavelength see my youtube channel: "mathwithmrv" if you want to know how to rearrange equations using the balance method
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hi pls help me with this question A ball is projected vertically upwards from the top of a tower 60m high with a velocity of 30ms1.what is the maximum height above the ground level?how long does it take to reach the ground level?
please guys help, what is the difference between concave lens and convex lens
Vincent Reply
convex lens brings rays of light to a focus while concave diverges rays of light
for mmHg to kPa yes
it depends on the size
Matthew Reply
please what is concave lens
a lens which diverge the ray of light
concave diverges light
thank you guys
A diverging lens
What is isotope
each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element. "some elements have only one stable isotope
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I would like to know this too
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Calculate . ..
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What is wave
What is light
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Great science students
A wave is a disturbance which travels through the medium transferring energy from one form to another without causing any permanent displacement of d medium itself
Light is a form o wave
Neurons communicate by sending message through nerves in coordination
What are petrochemicals, give two examples
light has dual nature, particle as well as wave. when we want to explain phenomena like Interference of light, then we consider light as wave.
what is it as in the form of it or how to visualize it or what it contains
particles of light are like small packets of energy called photons, and flow or motion of photons is wave like
light is just the energy of which photons emit
the wave is how they travel
photons do not emitt energy, they are energy. They are massless particles.
a wave is a disturbance through the medium. Have you ever thrown a stone in still water? the disturbance produced travels in form of wave, the wave produced by throwing stone in still water are circular in nature.
a photon does contain mass when in motion. it doesnt contain mass when at rest
when would it ever be at rest
a wave is a disturbance of which energy travels
that's darkness. darkness has no mass because the photons within in aren't moving or producing energy
Hi guys. Please I've been trying to understand the concept of SHM, but it's not been really easy, could someone please explain it to me or suggest a site I could visit? Thank you.
effective mass of photons only comes into picture when we consider it accelerating in gravitational field, mass of photon has no meaning as it is always travelling with speed of light and is never at rest. with that high speed, Energy and momentum are equivalent. and darkness is absense of photons.
darkness is absense of light. not the presence of 'resting photons'. photons are never at rest.
photons are present in darkness but don't give off any light because they are stationary with no mass or energy. once a force makes them move again they will gain mass and give off light
this theory is presented in Einsteins theory of special relativity
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Matthew, photons ARE light. there is no such thing as a photon that isn't moving. in fact the speed they move at is called C (for constant) in physics. through a vacuum they always travel at this speed no matter what. they can not slow down; except in another medium.
The reason why a photon can go at this speed is BECAUSE it had no mass. nothing can go this speed or faster because it needs to have no mass or negative mass. that's why it's called the constant.
when a photon hits something that is opaque, this is the only way to "stop"it. it isn't merely stopped but absorbed and turned into heat energy, then the remaining energy is reflected in different wavelengths. that reflection is what we call color. the darker something is, the less photons are ther
e. complete blackness is the absolute absence of photons altogether. I believe what you're referring to is not speed, but wavelength, which is indirectly proportional to the amount of energy a particular photon is made up of.
in order for a photon to have zero wavelength, it must (at least theoretically) have infinite energy.
about mass: you may have photons confused with electrons. elections have a mass so small that people say they are without mass, but they do. it is called electron mass or Me-.
you may also be getting electrons and photons confused because of the cherenkov effect. that is what happens when a particle travels faster than light IN THAT PARTICULAR MEDIUM. I emphasize that because no other particle besides photons can go the speed of c.
when a particle goes faster than light in a particular medium, a blue light is emitted, called cherenkov radiation. this is why nuclear reactors glow blue.
nuclear reactors release so much energy that when they emit electrons, those electrons are given enough energy to go faster than light in that medium (in this case water), releasing blue light. if you put the reactor in air or a vacuum, this effect wouldn't happen because the speed of light in air
is very close to c, which is the universal speed limit. I'd you did go faster than c, time would go backwards and you would have infinite theoretical mass and probably spagghettify, like with a black hole.
light waves can travel through a vacuum, and do not require a medium. In empty space, the wave does not dissipate (grow smaller) no matter how far it travels, because the wave is not interacting with anything else.
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pls he do we find for tension
Belinda Reply
tension is equal to the weight of the object. so for example if something weighs 45 Newtons then the tension in the Rope holding it is 45 Newtons. and because it is in equilibrium if the object is 45N and there are three ropes holding it there would be 15 N of tension in each to equal the weight
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very correct
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Aliyu Reply
the quantity of matter that a body contains, as measured by its acceleration under a given force or by the force exerted on it by a gravitational field.
I agree wth aliyu shuwa
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your mass never changes but your weight changes based on the gravitational pull of a system or planet. your mass is just the amount of matter with a certain object
please can someone help, why a bats can fly in the night without heating anything, how does he managed an see in darkness?
...hit an obstacle and has bounced back.
Hi Vincent. From what I can remember and what I've learnt, bats do not have a good eye sight and so they make use of waves, when they send out waves and they do not return back to them, they realise that the site is free of obstacles but if it sends a wave and it returns back, it means it hit an
obstacle and bounced back
So bats make use of waves in place of eye sight. I think but confirm from a few sites .
they us echolocation to make a sort of mental map. many sea animals use the same method. this can also be compared to sonar which works in the same way
y is atom d smallest particle
its a question Lajpat Rai
Google Quantum Physics or refer to the text
atoms are considered the smallest unit of matter. it is further divided into three subatomic particles: protons, neutrons, and electrons.
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Practice Key Terms 4

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