Pressure in Fluids PDF

Pressure in Fluids Pressure(P) is defined as the force per unit area. The units of pressure in the SI system are pascal (Pa) When the body is submerged, the Pressure is the same in every direction in a fluid at a given depth;...

Pressure in Fluids Pressure(P) is defined as the force per unit area. The units of pressure in the SI system are pascal (Pa) When the body is submerged, the Pressure is the same in every direction in a fluid at a given depth; if it were not, the fluid would flow. 20 The pressure at a depth h below the surface of the liquid is due to the weight of the liquid above it. We can quickly calculate pressure ‘P’ as Force m  g g  ρ × Volume P   ρ×g×h×A Area A A P= A Therefore, Pressure, P = ρgh The change in pressure ∆P due to change in depth ∆h, ∆P = ρg∆h Therefore, the pressure (P) on an object at a depth h below the surface in a liquid of density (ρ) is called ‘Guage pressure’given by 21 Dr. Syed Ismail Ahmad. PhD Atmospheric Pressure and Gauge Pressure At sea level the Atmospheric pressure (PA) or (1atm) is about Another unit of pressure is the bar: Standard atmospheric pressure is just over 1 bar. 1 atm = 𝟏. 𝟎𝟏𝟑 × 𝟏𝟎𝟓 𝐏𝐚 = 𝟕𝟔𝟎 𝐭𝐨𝐫𝐫 = 𝟏𝟒. 𝟕 𝐥𝐛/𝐢𝐧𝟐 This pressure does not crush us, as our cells which maintains an internal pressure that balances it. The absolute pressure (P) is the sum of the atmospheric pressure (PA) and the gauge pressure (PG). P=P +P 22 A G  Barometer This is a mercury barometer, developed by Torricelli to measure atmospheric pressure. The height of the column of mercury is such that the pressure in the tube at the surface level is 1 atm. Therefore, pressure is often quoted in millimeters (or inches) of mercury. Sphygmomanometer To measure the blood pressure 23  Measurement of Pressure; Gauges There are a number of different types of Atmospheric pressure gauges. pressure This one is an open-tube manometer. The pressure in the open end is atmospheric pressure(PA); the pressure being measured (P) called Absolute pressure will cause the fluid to rise until the pressures on both sides at the same height are equal. (P = PA + ρg∆h ) DR. S I AHMAD Absolute pressure, P = Atmospheric pressure PA+ Gauge pressure P (P = ρ g∆h) 24