Calculating Water Pressure from Speed: A Scientific Approach

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Discussion Overview

The discussion revolves around calculating the pressure exerted by water based on its speed, exploring both theoretical and practical aspects. Participants seek methods to derive pressure from water velocity, with references to relevant principles and equations.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant inquires about calculating water pressure from speed, indicating a need for a method similar to one used for wind speed.
  • Another suggests using Bernoulli's principle as a potential approach, although they note the need for additional information.
  • A participant proposes the dynamic pressure equation P = 1/2ρv² for incompressible fluids, emphasizing its applicability to water.
  • Concerns are raised regarding unit consistency, particularly when converting water speed from knots to feet per second for accurate pressure calculations.
  • One participant expresses confusion about the variables in the equation, specifically distinguishing between pressure (P) and density (ρ), indicating a need for clarification on the formula's components.
  • Another participant acknowledges their misunderstanding and thanks the contributor for the clarification regarding the Greek letter rho.

Areas of Agreement / Disagreement

Participants generally agree on the use of the dynamic pressure equation for calculating pressure from water speed, but there is some confusion regarding unit conversions and the interpretation of variables in the equation. The discussion remains somewhat unresolved as participants express differing levels of understanding.

Contextual Notes

Limitations include the need for consistent units and the potential misunderstanding of variables in the pressure equation. The discussion does not resolve these issues fully.

Who May Find This Useful

This discussion may be useful for individuals interested in fluid dynamics, engineering applications involving water pressure, or those seeking to understand the relationship between fluid speed and pressure calculations.

zeroonezero
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How do you calculate the pressure exerted by water if you know the speed?
 
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Its difficult to say without knowing more, but you might try

http://en.wikipedia.org/wiki/Bernoulli%27s_principle"
 
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What I really should have asked was: Since I calculate the pressure applied by a given wind speed by the following simple method:- Mph^2 * 0.0027 = psf so, is there a simple method to calculate the pressure applied by a given water speed? Thanks
 
If all you want to know is the dynamic pressure, then you can find it for any incompressible fluid (which includes most gases, so long as the speed in question is below about mach 0.3) by simply using the equation P = 1/2ρv2.
 
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Pardon my ignorance...the only thing I know is the speed of the water...6 knots...I have a plate 3ft sq facing that flow...How do I calculate the pressure on that plate, or any plate, in terms of psi or psf? P=1/2pv2 does not make sense to me since P, p is pressure
 
cjl said:
If all you want to know is the dynamic pressure, then you can find it for any incompressible fluid (which includes most gases, so long as the speed in question is below about mach 0.3) by simply using the equation P = 1/2ρv2.

In the formula above, the stagnation pressure P is a function of the density of the water (little p) and the velocity of the water. What you have to do is convert the velocity of the water from knots to units you can use with density in order to calculate the pressure P. If you use velocity in feet per second, for example, the density of the water must be in slugs per cubic foot. The resulting pressure will be in pounds per square foot.
 
zeroonezero said:
Pardon my ignorance...the only thing I know is the speed of the water...6 knots...I have a plate 3ft sq facing that flow...How do I calculate the pressure on that plate, or any plate, in terms of psi or psf? P=1/2pv2 does not make sense to me since P, p is pressure

In the equation P = 1/2ρv2, the ρ is not a p (see the difference?). It's a greek letter rho, which is the density of the fluid. As SteamKing said, you'll need to use consistent units in order for the answer to be correct.
 
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Oops! Did not catch that...Thanks...
 

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