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Static Pressure Head The formula for the pressure exerted is: Where D is the density of the fluid, h is the height, and g = 9.8 m/s 2.
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Measuring PressureMeasuring PressureSPH4C
Static Pressure HeadStatic Pressure HeadFor any point in a static fluid, the
height of the column above that point is called the static pressure head.
A dam must be thicker or stronger at greater depths to withstand the increased pressure.
Static Pressure HeadStatic Pressure HeadThe formula for the pressure
exerted is:
Where D is the density of the fluid,h is the height, and g = 9.8 m/s2.
DhgA
ghADAgVD
Amg
AFp
BarometersBarometersIn mercury barometers, it is the
static pressure head that indicates the external air pressure.
The higher the atmospheric pressure, the higher the static pressure head.
BarometersBarometersIn mercury barometers, it is the
static pressure head that indicates the external air pressure.
The higher the atmospheric pressure, the higher the static pressure head.
Question: Why do we use mercury in barometers instead of water?
Water LevelWater LevelLiquid in connected containers
exposed to the same air pressure will be at the same height.
The shape and orientation of the containers makes no difference to the height.
SiphonsSiphonsThis is often phrased as “water
seeks its own level,” and is why water will even flow uphill in a siphon if it can reach a lower point at the end of the siphon.
Note that the siphon needs to be full of liquid to connect the two containers.
ManometersManometersManometers can be used to
measure variations in pressure.
When more pressure is applied to the left side of the tube, there will be a difference in the heights of the liquid.
Gauge pressureGauge pressureThis variation in pressure from
atmospheric pressure is called the gauge pressure:
atmabsg ppppressurecatmospheripressureabsolutepressuregauge
Tire pressure gauges measure gauge pressure: the pressure over and above atmospheric pressure.
Gauge pressure exampleGauge pressure examplePressure is applied to one end of a
water manometer so that the difference between the two heights is 10 cm.
(a) What is the gauge pressure applied?
(b) What is the absolute pressure applied?
Gauge pressure exampleGauge pressure example(a) What is the gauge pressure
applied?
2
3
8.910.0
1000
sm
mkg
gmh
D
Gauge pressure exampleGauge pressure example(a) What is the gauge pressure
applied?
2
3
8.910.0
1000
sm
mkg
gmh
D
Gauge pressure exampleGauge pressure example(a) What is the gauge pressure
applied?
2
3
8.910.0
1000
sm
mkg
gmh
D
kPaor
PamDhgpsm
mkg
980.0
980)8.9)(10.0)(1000( 23
Gauge pressure exampleGauge pressure example(b) What is the absolute pressure
applied?
kPakPakPa
ppp atmgabs
28.1023.101980.0