# What is Static Pressure? - Definition & Formula Video

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• 0:03 Definition of Static Pressure
• 1:29 Measuring Static Pressure
• 3:20 Lesson Summary
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Lesson Transcript
Instructor: John Parsons

John has taught physics to both engineers and non-engineers, and has a master's degree in Civil and Environmental Engineering.

Static pressure is the pressure that a fluid exerts when it is not moving. This lesson looks at the definition of static pressure as well as how to compute the pressure.

## Definition of Static Pressure

Static pressure, or hydrostatic pressure as it is sometimes called, is the pressure exerted by a fluid at rest. A fluid is any substance that does not conform to a fixed shape. This can be a liquid or a gas. Since the fluid is not moving, static pressure is the result of the fluid's weight or the force of gravity acting on the particles in the fluid.

There are two different ways to measure static pressure. The first (and most common) measure is to take the force exerted by the fluid and divide it by the area over which it is acting. A second common method for computing static pressure is to compute the pressure head, which is sometimes called the head, and what you can see in the image.

The pressure head is how high the fluid will go up if the forces confining the fluid are removed. Therefore, it has units usually associated with length. Pressure and pressure head are mathematically related. That relationship is shown by these equations:

Dividing the pressure by the unit weight of the fluid gives us the pressure head associated with that pressure. Unit weight (also known as specific weight) is the weight per unit volume of fluid. This is a constant unique for each individual fluid.

## Measuring Static Pressure

Static pressure is the weight of the fluid above the point that is being examined. To compute the pressure, use this equation (which is a rearrangement of the pressure head equation):

The figure and the equation show that the further you look below the surface of the fluid the greater the hydrostatic pressure. It's important to note that this equation only works for noncompressible fluids, or fluids whose density does not change with time. This equation will work for compressible fluids (fluids whose density change with time), but only over short distances.

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