PRESSURE

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Pressure Terminology 
P=ρgh
There are three different kinds of pressure reported in the literature, and it is important to know the terminology:
1.      Absolute pressure is measured relative to absolute zero on the pressure scale, which is a perfect vacuum. (Absolute pressure can never be negative.) Absolute pressure is indicated by P and is identical to the familiar thermodynamic pressure.

2.      Gage pressure (sometimes written as "gauge pressure") is measured relative to the local atmospheric pressure. Gage pressure is thus zero when the pressure is the same as atmospheric pressure. (It is possible to have negative gage pressure.) Gage pressure is indicated by Pg and is related to absolute pressure as follows: Pg = P - Pa, where pa is the local atmospheric pressure.

3.      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.) Vacuum pressure is indicated by Pvacuum and is related to absolute pressure as follows: Pvacuum = Pa - P, where pa is the local atmospheric pressure.

Ptotal​=ρgh+Patm​


EXAMPLE
1.      Pressure acting in water at depth 1 m. The density of water at 4oC is 1000 kg/m3. The pressure acting in water at 1 m can be calculated as
Solution:
p = ρ g h 
   = (1000 kg/m3) (9.81 m/s2) (1 m) 
   = 9810 Pa


2.      Pressure acting in water at depth 3 ft. The density of water at 32oF is 1.940 slugs/ft3. The pressure acting in water at 3 ft can be calculated as
Solution:
p = ρ g h
   = (1.940 slugs/ft3) (32.17405 ft/s2) (3 ft) 
   = 187.3 lbf/ft2 (psf)
   = 1.3 lbf/in2 (psi)

ABOUT US

We are students of Bachelor Degree of Civil Engineering Technology (Environmental) with Honours from University Tun Hussein Onn Malaysia. Our teammates are:

1. MUHAMMAD AFIQ BIN ZABIDI (AN170093)

2. MUHAMMAD ARIF RIDZUAN BIN MD KHALIL (AN170061)

3. NUR IZZAH BINTI MOHAMAD KETAR @ MOKHTAR (AN170125)

4. NUR LAILA BINTI OSMAN (AN170083)

5. NUR IZZMIRZA BINTI MOHSIN (CN170013)

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