# Pressure length relationship

### fluid dynamics - Does length of a hosepipe affect pressure/flow - Physics Stack Exchange

In fluid dynamics, the Darcy–Weisbach equation is an empirical equation, which relates the head loss, or pressure loss, due to friction along a given length of. Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit The force given by the previous relationship to the quantity has a direction, but the pressure does not. Note that the pressure conversion from msw to fsw is different from the length conversion: 10 msw = fsw, while [The volume, volume extensibility and the pressure-length relationship of the total aortic expansion chamber in relation to age, hypertension and arteriosclerosis].

Pressure Change due to Velocity Change Fluid velocity will change if the internal flow area changes. For example, if the pipe size is reduced, the velocity will increase and act to decrease the static pressure.

If the flow area increases through an expansion or diffuser, the velocity will decrease and result in an increase in the static pressure. If the pipe diameter is constant, the velocity will be constant and there will be no change in pressure due to a change in velocity.

As an example, if an expansion fitting increases a 4 inch schedule 40 pipe to a 6 inch schedule 40 pipe, the inside diameter increases from 4.

If the flow rate through the expansion is gpm, the velocity goes from 9. The change in static pressure across the expansion due to the change in velocity is: In other words, pressure has increased by almost 0. Pressure Change due to Head Loss Since head loss is a reduction in the total energy of the fluid, it represents a reduction in the capability of the fluid to do work. Head loss does not reduce the fluid velocity consider a constant diameter pipe with a constant mass flow rateand it will not be effect the elevation head of the fluid consider a horizontal pipe with no elevation change from inlet to outlet.

**Poiseuille's Law - Pressure Difference, Volume Flow Rate, Fluid Power Physics Problems**

Therefore, head loss will always act to reduce the pressure head, or static pressure, of the fluid. There are several ways to calculate the amount of energy lost due to fluid flow through a pipe. The negative gradient of pressure is called the force density.

Another example is a knife. If we try to cut a fruit with the flat side, the force is distributed over a large area, and it will not cut. But if we use the edge, it will cut smoothly.

### Darcy–Weisbach equation - Wikipedia

The reason is that the flat side has a greater surface area less pressureand so it does not cut the fruit. When we take the thin side, the surface area is reduced, and so it cuts the fruit easily and quickly. This is one example of a practical application of pressure.

For gases, pressure is sometimes measured not as an absolute pressure, but relative to atmospheric pressure ; such measurements are called gauge pressure. Where space is limited, such as on pressure gaugesname platesgraph labels, and table headings, the use of a modifier in parentheses, such as "kPa gauge " or "kPa absolute ", is permitted.

## Darcy–Weisbach equation

However, whenever equation-of-state properties, such as densities or changes in densities, must be calculated, pressures must be expressed in terms of their absolute values. Focusing on gauge values, one might erroneously conclude the first sample had twice the density of the second one.

Scalar nature[ edit ] In a static gasthe gas as a whole does not appear to move.