# 1.5 Gauge pressure, absolute pressure, and pressure measurement  (Page 2/7)

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An entire class of gauges uses the property that pressure due to the weight of a fluid is given by $P=\mathrm{h\rho g}\text{.}$ Consider the U-shaped tube shown in [link] , for example. This simple tube is called a manometer . In [link] (a), both sides of the tube are open to the atmosphere. Atmospheric pressure therefore pushes down on each side equally so its effect cancels. If the fluid is deeper on one side, there is a greater pressure on the deeper side, and the fluid flows away from that side until the depths are equal.

Let us examine how a manometer is used to measure pressure. Suppose one side of the U-tube is connected to some source of pressure ${P}_{\text{abs}}$ such as the toy balloon in [link] (b) or the vacuum-packed peanut jar shown in [link] (c). Pressure is transmitted undiminished to the manometer, and the fluid levels are no longer equal. In [link] (b), ${P}_{\text{abs}}$ is greater than atmospheric pressure, whereas in [link] (c), ${P}_{\text{abs}}$ is less than atmospheric pressure. In both cases, ${P}_{\text{abs}}$ differs from atmospheric pressure by an amount $\mathrm{h\rho g}$ , where $\rho$ is the density of the fluid in the manometer. In [link] (b), ${P}_{\text{abs}}$ can support a column of fluid of height $h$ , and so it must exert a pressure $\mathrm{h\rho g}$ greater than atmospheric pressure (the gauge pressure ${P}_{\text{g}}$ is positive). In [link] (c), atmospheric pressure can support a column of fluid of height $h$ , and so ${P}_{\text{abs}}$ is less than atmospheric pressure by an amount $\mathrm{h\rho g}$ (the gauge pressure ${P}_{\text{g}}$ is negative). A manometer with one side open to the atmosphere is an ideal device for measuring gauge pressures. The gauge pressure is ${P}_{\text{g}}=\mathrm{h\rho g}$ and is found by measuring $h$ .

Mercury manometers are often used to measure arterial blood pressure. An inflatable cuff is placed on the upper arm as shown in [link] . By squeezing the bulb, the person making the measurement exerts pressure, which is transmitted undiminished to both the main artery in the arm and the manometer. When this applied pressure exceeds blood pressure, blood flow below the cuff is cut off. The person making the measurement then slowly lowers the applied pressure and listens for blood flow to resume. Blood pressure pulsates because of the pumping action of the heart, reaching a maximum, called systolic pressure    , and a minimum, called diastolic pressure    , with each heartbeat. Systolic pressure is measured by noting the value of $h$ when blood flow first begins as cuff pressure is lowered. Diastolic pressure is measured by noting $h$ when blood flows without interruption. The typical blood pressure of a young adult raises the mercury to a height of 120 mm at systolic and 80 mm at diastolic. This is commonly quoted as 120 over 80, or 120/80. The first pressure is representative of the maximum output of the heart; the second is due to the elasticity of the arteries in maintaining the pressure between beats. The density of the mercury fluid in the manometer is 13.6 times greater than water, so the height of the fluid will be 1/13.6 of that in a water manometer. This reduced height can make measurements difficult, so mercury manometers are used to measure larger pressures, such as blood pressure. The density of mercury is such that $1.0 mm Hg=133\phantom{\rule{0.25em}{0ex}}\text{Pa}$ .

where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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