**Pressure**is typically

**measured**in units of force per unit of surface area. Instruments used to

**measure**and display

**pressure**in an integral unit are called

**pressure**gauges or vacuum gauges. A manometer is a good example as it uses a column of liquid to both

**measure**and indicate

**pressure**.

1

## How do you measure the pressure?

The SI unit for

**pressure**is the Pascal (N/m2), but other common units of**pressure**include pounds per square inch (PSI), atmospheres (atm), bars, inches of mercury (in Hg), and millimeters of mercury (mm Hg). A**pressure measurement**can be described as either static or dynamic.2

## How do you measure air pressure?

An instrument that measures

**air pressure**is called a barometer. One of the first barometers was developed in the 1600s. The original instrument had mercury in the small basin, with an upside down glass tube placed in the mercury. As**air pressure**increased, the**pressure**would force more mercury in the tube.3

## How do you measure pressure?

The standard SI unit for

**pressure measurement**is the Pascal (Pa) which is equivalent to one Newton per square meter (N/m2) or the KiloPascal (kPa) where 1 kPa = 1000 Pa. In the English system,**pressure**is usually expressed in pounds per square inch (psi).5

## How do you measure the pressure of gas?

If it

**measures pressure**exerted upon a column of liquid, it is called a manostat, or manometer. Atmospheric**pressure**is often**measured**in millibars. Thus, the gauge used to**measure**atmospheric**pressure**is a form of manometer called a barometer.6

## What is the cause of pressure in fluids?

**Fluid pressure**is a measurement of the force per unit area.

**Fluid pressure**can be caused by gravity, acceleration, or forces in a closed container. Since a

**fluid**has no definite shape, its

**pressure**applies in all directions.

7

## What is manometer used to measure?

**Manometers**are devices in which columns of a suitable liquid are used to

**measure**the difference in pressure between two points or between a certain point and the atmosphere.

**Manometer**is needed for

**measuring**large gauge pressures. It is basically the modified form of the piezometric tube.

8

## What is the unit of absolute pressure?

An example of this is the air

**pressure**in an automobile tire, which might be said to be "220 kPa (32 psi)", but is actually 220 kPa (32 psi) above atmospheric**pressure**. Since atmospheric**pressure**at sea level is about 100 kPa (14.7 psi), the**absolute pressure**in the tire is therefore about 320 kPa (46.7 psi).9

## How do you find the atmospheric pressure?

**Measurements**from a mercury barometer are usually made in inches of Mercury (in Hg). An aneroid barometer can be used in place of a mercury barometer. It is easier to move and is often easier to read. This instrument contains sealed wafers that shrink or spread out depending on changes of

**atmospheric pressure**.

10

## How much is atmospheric pressure?

Standard sea-level pressure, by definition, equals 760 mm (29.92 inches) of mercury,

**14.70 pounds**per square inch, 1,013.25 × 10^{3}dynes per square centimetre, 1,013.25 millibars, one standard atmosphere, or 101.325 kilopascals.11

## What is the difference between absolute pressure and gauge pressure?

**Absolute pressure is**zero-referenced against a perfect vacuum, so it

**is equal**to

**gauge pressure**plus atmospheric

**pressure**.

**Gauge pressure is**zero-referenced against ambient air

**pressure**, so it

**is equal**to

**absolute pressure**minus atmospheric

**pressure**. Negative signs

**are**usually omitted.

12

## What is air pressure and how is it measured?

(atm) unit of measurement equal to air pressure at sea level, about

**14.7 pounds per square inch**. Also called standard atmospheric pressure. force per unit area exerted by the mass of the atmosphere as gravity pulls it to Earth.13

## What is the gauge pressure?

**Gauge pressure**is a relative

**pressure**measurement which measures

**pressure**relative to atmospheric

**pressure**and is defined as the absolute

**pressure**minus the atmospheric

**pressure**. Most

**pressure**measuring equipment give the

**pressure**of a system in terms of

**gauge pressure**as opposed to absolute

**pressure**.

14

## What is the formula for absolute pressure?

Any

**pressure**measured above the**absolute**zero of**pressure**is called as**absolute pressure**.The**absolute pressure**is equal to gauge**pressure**plus the atmospheric**pressure**. It is measured using barometer.**Absolute pressure formula**(P abs) is. P abs = P atm+ P gauge.15

## What is the difference between gauge pressure and atmospheric pressure?

Absolute

**pressure**is zero-referenced against a perfect vacuum, so it is equal to**gauge pressure**plus**atmospheric pressure**.**Gauge pressure**is zero-referenced against**ambient**air**pressure**, so it is equal to absolute**pressure**minus**atmospheric pressure**. Negative signs are usually omitted.16

## What is not a unit of pressure?

**Pressure**—the effect of a force applied to a surface—is a derived

**unit**, obtained from combining base

**units**. The

**unit of pressure**in the SI system is the pascal (Pa), defined as a force of one Newton per square meter. The conversion between atm, Pa, and torr is as follows: 1 atm = 101325 Pa = 760 torr.

17

## What does it mean to have negative gauge pressure?

Vacuum

**pressure**is also measured relative to the local atmospheric**pressure**, but is used when the**gage pressure**is**negative**, i.e. when the absolute**pressure**falls below the local atmospheric**pressure**. (Positive vacuum**pressure means**that the**gage pressure**is**negative**.)18

## What is the value of absolute zero pressure?

It appeared that an “ideal gas” at constant

**pressure**would reach**zero**volume at what is now called the**absolute zero**of temperature. Any real gas actually condenses to a liquid or a solid at some temperature higher than**absolute zero**; therefore, the ideal gas law is only an approximation to real gas behaviour.