A centimetre or millimetre of water (US spelling ''centimeter'' or ''millimeter of water'') are less commonly used measures of

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

derived from

pressure head In fluid mechanics, pressure head is the height of a liquid column that corresponds to a particular pressure exerted by the liquid column on the base of its container. It may also be called static pressure head or simply static head (but not ''sta ...

Centimetre of water

A ''centimetre of water'' (US spelling ''centimeter of water'')NOTE: A centimetre of water is abbreviated as ''cm'' or ''cm H₂O''. is a unit of pressure. It may be defined as the pressure exerted by a column of

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

of 1 cm in

height Height is measure of vertical distance, either vertical extent (how "tall" something or someone is) or vertical position (how "high" a point is). For example, "The height of that building is 50 m" or "The height of an airplane in-flight is abou ...

at 4

°C The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The ...

(temperature of maximum density) at the standard acceleration of gravity, so that = × × 1 cm = ≈ , but conventionally a nominal maximum water density of is used, giving . The centimetre of water unit is frequently used to measure the

central venous pressure Central venous pressure (CVP) is the blood pressure in the venae cavae, near the right atrium of the heart. CVP reflects the amount of blood returning to the heart and the ability of the heart to pump the blood back into the arterial system. CVP ...

, the

intracranial pressure Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury (mmHg) and at rest, is normally 7–15 Millimeter of mercury, mmHg ...

while sampling

cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the bra ...

, as well as determining pressures during

mechanical ventilation Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (IMV), is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move a ...

or in

water supply network A water supply network or water supply system is a system of engineered hydrologic and hydraulic components that provide water supply. A water supply system typically includes the following: # A drainage basin (see water purification – source ...

s (then usually in

metre The metre (British spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its pref ...

s water column). It is also a common unit of pressure in the

speech science Speech science refers to the study of production, transmission and perception of speech. Speech science involves anatomy, in particular the anatomy of the oro-facial region and neuroanatomy, physiology, and acoustics. Speech production The pro ...

s. This unit is commonly used to specify the pressure to which a

CPAP Continuous positive airway pressure (CPAP) is a form of positive airway pressure (PAP) ventilation in which a constant level of pressure greater than atmospheric pressure is continuously applied to the upper respiratory tract of a person. The ap ...

machine is set after a

polysomnogram Polysomnography (PSG), a type of sleep study, is a multi-parameter study of sleep and a diagnostic tool in sleep medicine. The test result is called a polysomnogram, also abbreviated PSG. The name is derived from Greek and Latin roots: the Gree ...

. :

Millimetre of water

''Millimetre of water'' (US spelling ''millimeter of water'')NOTE: Millimetre of water is also sometimes addressed as : ''millimetres water column'', abbreviated as ''mmwg'', ''mmH₂O'', or ''mmwc''. is a unit of pressure. It may be defined as the pressure exerted by a column of

of 1 mm in

at 4

(temperature of maximum density) at the standard acceleration of gravity, so that = × × 1 mm = ≈ , but conventionally a nominal maximum water density of is used, giving . : In limited and largely historic contexts it may vary with

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

, using the equation: : ''P'' = ''ρ''·''g''·''h''/1000, : where : ''P'': pressure in Pa : ''ρ'': density of water (conventionally 1000 kg/m³ at 4 °C) : ''g'': acceleration due to gravity (conventionally 9.80665 m/s² but sometimes locally determined) : ''h'': water height in millimetres. The unit is often used to describe how much water rainwear or other

outerwear Outerwear is clothing and accessories worn outdoors, or clothing designed to be worn outside other garments, as opposed to underwear. It can be worn for formal or casual occasions, or as warm clothing during winter. List of outerwear * Academic ...

can take or how much water a

tent A tent () is a shelter consisting of sheets of fabric or other material draped over, attached to a frame of poles or a supporting rope. While smaller tents may be free-standing or attached to the ground, large tents are usually anchored using gu ...

can resist without leaking.

References

{{reflist

External links

Pressure conversion calculator
at

Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teach an ...

website Units of pressure

Centimetre of water

Millimetre of water

See also

References

External links