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Name: Colin
Status: Student
Grade: Other
Location: VA
Country: United States
Date: June 2006

Hi, am doing a science project on how the velocity of the flow of water through a pipe is affected by the pipe's inclination to the horizontal. Can you please tell me how the angle of inclination affects the velocity of the water and how to calculate this velocity?


The answer to your question can be extremely complicated indeed, depending on a number of things you have not made clear about the experiment. Without knowing the full details, it is really not possible to begin to answer this question.

As a general statement, water entering from (for example) a large tank into a pipe that is open at the lower end, will flow increasingly fast as you tilt the pipe more downward. This results from what is called the "pressure head" caused by the weight of the vertical component of the column of water. Greater pressure (caused by a greater inclination, and hence a greater vertical drop) causes the water to flow faster.

But how much faster? There is no simple formula for this, and in fact, most common way to solve this these days involves using extremely expensive Computational Fluid Dynamics analysis software. Some things that we need to know, are:

- How is the water entering the pipe? Gravity or pump?
- If it is being pumped, what is the pressure/volume characteristics of the pump?
- What is the diameter of the pipe?
- What is the surface roughness of the pipe?
- What is the length of the pipe?
- Which direction is the pipe inclined ("up" or "down"?)

Sorry to answer your question with more questions, but this is actually something that university physics students scratch their heads on. There is unfortunately no simple formula for velocity of water in a pipe!


Bob Wilson

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