Note that pressure is directly proportional to force and inversely proportional to area.Thus, pressure can be increased either by increasing the amount of force or by decreasing the area over which it is applied; pressure can be decreased by decreasing the force or increasing the area.
Let’s apply this concept to determine which would be more likely to fall through thin ice in Figure 2—the elephant or the figure skater?
A large African elephant can weigh 7 tons, supported on four feet, each with a diameter of about 1.5 ft (footprint area of 250 in Even though the elephant is more than one hundred-times heavier than the skater, it exerts less than one-half of the pressure and would therefore be less likely to fall though thin ice.
One of the most common is the water filled u-tube manometer used to measure pressure difference in pitot or orifices located in the airflow in air handling or ventilation system.
In the figure bellow illustrates the water levels in an u-tube where the left tube is connected to a point with higher pressure than the right tube - example: the left tube may be connected to a pressurized air duct when the right tube is open to the ambient air.
The difference height in the water column is 10 mm.
The pressure difference head can calculated from (1) as A common problem when measuring the pressure difference in low velocity systems - or systems with low density fluids - like air ventilation systems - are low column heights and accuracy.
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Manometers measure a pressure difference by balancing the weight of a fluid column between the two pressures of interest.
Large pressure differences are measured with heavy fluids, such as mercury (e.g. Small pressure differences, such as those experienced in experimental wind tunnels or venturi flowmeters, are measured by lighter fluids such as water (27.7 inch HO = 98.1 Pa).