# 11.9 Pressures in the body  (Page 2/11)

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Standing a long time can lead to an accumulation of blood in the legs and swelling. This is the reason why soldiers who are required to stand still for long periods of time have been known to faint. Elastic bandages around the calf can help prevent this accumulation and can also help provide increased pressure to enable the veins to send blood back up to the heart. For similar reasons, doctors recommend tight stockings for long-haul flights.

Blood pressure may also be measured in the major veins, the heart chambers, arteries to the brain, and the lungs. But these pressures are usually only monitored during surgery or for patients in intensive care since the measurements are invasive. To obtain these pressure measurements, qualified health care workers thread thin tubes, called catheters, into appropriate locations to transmit pressures to external measuring devices.

The heart consists of two pumps—the right side forcing blood through the lungs and the left causing blood to flow through the rest of the body ( [link] ). Right-heart failure, for example, results in a rise in the pressure in the vena cavae and a drop in pressure in the arteries to the lungs. Left-heart failure results in a rise in the pressure entering the left side of the heart and a drop in aortal pressure. Implications of these and other pressures on flow in the circulatory system will be discussed in more detail in Fluid Dynamics and Its Biological and Medical Applications .

## Two pumps of the heart

The heart consists of two pumps—the right side forcing blood through the lungs and the left causing blood to flow through the rest of the body.

## Pressure in the eye

The shape of the eye is maintained by fluid pressure, called intraocular pressure    , which is normally in the range of 12.0 to 24.0 mm Hg. When the circulation of fluid in the eye is blocked, it can lead to a buildup in pressure, a condition called glaucoma    . The net pressure can become as great as 85.0 mm Hg, an abnormally large pressure that can permanently damage the optic nerve. To get an idea of the force involved, suppose the back of the eye has an area of $6\text{.}0\phantom{\rule{0.25em}{0ex}}{\text{cm}}^{2}$ , and the net pressure is 85.0 mm Hg. Force is given by $F=\text{PA}$ . To get $F$ in newtons, we convert the area to ${\text{m}}^{2}$ ( ${\text{1 m}}^{2}={\text{10}}^{4}\phantom{\rule{0.25em}{0ex}}{\text{cm}}^{2}$ ). Then we calculate as follows:

$F=\mathrm{h\rho }\text{gA}=\left(\text{85}\text{.}0×{\text{10}}^{-3}\phantom{\rule{0.25em}{0ex}}\text{m}\right)\left(\text{13}\text{.}6×{\text{10}}^{3}\phantom{\rule{0.25em}{0ex}}{\text{kg/m}}^{3}\right)\left(9\text{.}\text{80}\phantom{\rule{0.25em}{0ex}}{\text{m/s}}^{2}\right)\left(6\text{.}0×{\text{10}}^{-4}\phantom{\rule{0.25em}{0ex}}{\text{m}}^{2}\right)=6.8 N.$

## Eye pressure

The shape of the eye is maintained by fluid pressure, called intraocular pressure. When the circulation of fluid in the eye is blocked, it can lead to a buildup in pressure, a condition called glaucoma. The force is calculated as

$F=\mathrm{h\rho }\text{gA}=\left(\text{85}\text{.}0×{\text{10}}^{-3}\phantom{\rule{0.25em}{0ex}}\text{m}\right)\left(\text{13}\text{.}6×{\text{10}}^{3}\phantom{\rule{0.25em}{0ex}}{\text{kg/m}}^{3}\right)\left(9\text{.}\text{80}\phantom{\rule{0.25em}{0ex}}{\text{m/s}}^{2}\right)\left(6.0×{\text{10}}^{-4}\phantom{\rule{0.25em}{0ex}}{\text{m}}^{2}\right)=6.8 N.$

A body travelling at a velocity of 30ms^-1 in a straight line is brought to rest by application of brakes. if it covers a distance of 100m during this period, find the retardation.
what's acceleration
The change in position of an object with respect to time
Mfizi
Acceleration is velocity all over time
Pamilerin
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Stephen
It's not It's the change of velocity relative to time
Laura
Velocity is the change of position relative to time
Laura
acceleration it is the rate of change in velocity with time
Stephen
acceleration is change in velocity per rate of time
Noara
what is ohm's law
Stephen
Ohm's law is related to resistance by which volatge is the multiplication of current and resistance ( U=RI)
Laura
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How do you determine the magnitude of force
mass × acceleration OR Work done ÷ distance
Seema
Which eye defect is corrected by a lens having different curvatures in two perpendicular directions?
acute astigmatism?
the difference between virtual work and virtual displacement
How do you calculate uncertainties
What is Elasticity
using a micro-screw gauge,the thickness of a piece of a A4 white paper is measured to be 0.5+or-0.05 mm. If the length of the A4 paper is 26+or-0.2 cm, determine the volume of the A4 paper in: a). Cubic centimeters b). Cubic meters
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why it is possible for an object(man) to stay on air without falling down?
its impossible, what do you mean exactly?
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it's impossible
Your
Why is it not possible to stand in air?
bikko
the air molecules are very light enough to oppose the gravitational pull of the earth on the man..... hence, freefall occurs
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because of gravitational forces
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this mostly occur in space
Stephen
what is physics
no life without physics ....that should tell you something
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E=MC^2
study of matter and energy and an inter-relation between them.
Minahil
that's how the mass and energy are related in stationery frame
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Kinetic energy is the energy due to montion of waves,electrons,atoms, molecule,substances an object s.
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meteor are the glowy (i.e. heated when the enter into our atmosphere) parts of meteoroids. now, meteoroids are the debris resulting from the collision of asteroids or comets. yes, it occurs in daytime too, but due to the daylight, we cant observe it as clearly as in night
Arzail
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wich method we use to find the potential on a grounded sphere
Noman
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Pamilerin
Physics is the science that studies everything around us from the smallest things like quarks to the biggest things like galaxies. It's simply everything.
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Divine
It talks mainly about matter with related topics such as forces energy gravity and time. It's amazing
Laura
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Alpha
Physics generally is the study of everything around us.
Steven
physics is the branch of sceince
shafiu
physics is the branch of sceince that deal with motion
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physics is the branch of sceince that deal with motion &energy
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Emmanuella
the study of all the natural events occuring around us..... this is Physics (until those events obey the laws of physics)
Arzail
Conservation of energy😰
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Energy, it always remains there in a physical system. it can only take the form either in motion (kinetic energy) or in rest (potential energy)
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In nature organisms feed on one another in an orderly way.
Emmanuella
that describes the food chain, in which we humans are at the top
Arzail
The energy that came initially from the sun 🌞is converted into a form in which it can be stored in green plant.
Emmanuella
Therefore, there is conservation of energy.
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