Unit of Pressure

Pressure

The force per unit area is known as pressure. For many natural and man-made events, pressure is the primary driving force. Pressure is what causes cyclones and storms to form, and it’s also the basis for many modern inventions like hydraulic power jacks and rocket propulsion systems.

Stress is a term that is occasionally used to describe pressure. In terms of material science, stress is the applied pressure. As a result, pressure is a physical quantity with numerous applications in various domains. Throughout history, several pressure measurement systems have been used. Some of the units are still in use today, despite the fact that the systems were standardised.

The region on which the force is acting determines a substantial percentage of the pressure applied to the object. For example, if you hold a knife by the blade and use the handle to flatten an object (such a vegetable), the knife will not cut through it. If the sharp edge of the knife is placed on the object and the same force is applied, the knife will easily cut through it.

This is because, despite the same applied force, when the knife’s sharp edge is used, the area of the knife in contact with the object is smaller. This concentrates the force applied over a smaller area, delivering more impact and cutting through the object.

Formula of Pressure

P = FA 

Here,

P= pressure on the body

F= force applied on the body

A= area on which the pressure is applied

Pressure is a scalar quantity since it can only be measured in terms of magnitude and has no direction. Even if the object’s orientation is altered, just the direction in which the force exerts on it is altered, but the pressure stays unchanged. Pressure has the dimension [M L-1 T-2], and it is a physical quantity.

SI unit of Pressure

Internal pressure in a container, stress experienced by an object, Young’s modulus of an object or material, and ultimate tensile strength of a material are all measured using the SI unit of pressure, pascal (Pa). Blaire Pascal, a French physicist, inspired the unit’s name.

1 Pa = 1 N/ m2 = 1 kg/ ms2

CGS Unit Of Pressure

The CGS unit of pressure is the barye (Ba). It goes by a variety of names around the world, including baryd, baryed, barad, barrie, barie, and bary.

It is expressed as 

1 Ba=1 dyn/cm2 

The force required to accelerate a mass of 1gm to a speed of 1 cm per second is referred to as dyne.

Also, 

1 Pa = 0.1 Ba

Some other units of Pressure

Pound force per square inch: It’s the amount of force applied to a one-square-inch area when one pound of force is applied. It’s written as psi. Psi is divided into multiples that are utilized in various fields.

1ksi=6.895MPa 

1 MPa = 0.145 ksi 

1Mpsi=6.895GPa 

1 GPa = 0.145 Mpsi 

Here,

• ksi = kilo pound per square inch 

• MPa = mega pascal

• Mpsi = mega pound per square inch

• GPa = giga pascal

Standard Atmospheres (atm): Standard atmospheres (atm) are used to measure atmospheric pressure. Despite the fact that atmospheric pressure is measured in pascals (Pa), standard atmosphere (atm) is used for convenience and clarity. For example, it is more logical to say that a container has 100 atm (100 times the air pressure of the present atmospheric pressure) rather than 100 pascals of pressure.

In terms of pascals, a standard environment is expressed as:

1 atm = 101,325 Pa

Originally, this number was calculated for air pressure at sea level at 0°C.

When a precise measurement of pressure is not required, atmospheres are commonly employed. It’s a primitive and inefficient unit of measurement.

Bar (bar): The bar is a metric unit that has long been used in meteorology. It comes from the Greek word ‘baros,’ which means “weight.” Because 1 mbar equals 100 pascals, the unit mbar may simply be converted to pascals. Some vacuum equipment that operates under pressure uses mbar as a unit of measurement.

In terms of pascals, bars can be written as:

1 bar = 100,000 Pa

Torr: The Torr is a pressure measuring unit named after Evangelista Torricelli, the inventor of the barometer (device to measure air pressure). It’s most commonly used to measure low-pressure readings in milli-torrs (mTorr).

1 Torr is about equivalent to 1 mm Hg (mercury rise when unit pressure acts on it)

As a result, Torr can be written as:

1 atm = 760 Torr

1 Pa = 0.00750062 Torr

Pièze (pz): It’s an antique measurement method that’s been used since the early 1800s, mainly in France. 1 sthène per square metre (sn/m2) is the pièze’s definition.

In pascals, it’s written as:

1 pz = 1kPa.

Technical Atmosphere: These are non-SI unit systems that are no longer in use. These are the international equivalents of the American pressure measurement system (psi). The kilogram-force per square centimetre is the unit of measurement.

The technical atmosphere can be described as follows:

 1 at = 0.97 atm

Manometric Units

Manometric units are those that are calculated by measuring how much a liquid rises when pressure is applied to it. It’s measured in millimetres. Mercury (Hg) was employed as a liquid medium in the past. Manometer units are not particularly accurate because the temperature and density of liquid fluctuate from place to place.

Conclusion

In physics, pressure refers to the amount of force exerted to an object’s surface area in a normal direction. To put it another way, it’s the force delivered per unit of area. As a result, it differs from the total force acting on a surface. Single point stress can also be applied to a solid and maintained.

Nonetheless, only pressure can overcome the surface of a sealed substance, such as a fluid or gas. As a result, it is more appropriate to characterise the forces that work on and within the fluids in terms of pressure.