Bernoulli equation and velocity problem

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Discussion Overview

The discussion revolves around the Bernoulli equation, specifically focusing on the calculation of the pressure energy term within the equation. Participants explore the relationship between velocity, mass, and pressure in the context of energy calculations, seeking clarity on how to derive pressure energy from given values.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that velocity is measured in m/s and mass in N, leading to energy expressed in joules, but seeks clarification on the formula for calculating pressure energy in the Bernoulli equation.
  • Another participant references a Wikipedia page on Bernoulli's principle, possibly suggesting it as a resource for understanding the topic.
  • A participant explains that the terms in Bernoulli's equation represent energy per unit volume and that density is mass per unit volume, indicating a need to multiply by volume to convert to energy terms.
  • Several participants express confusion about how to calculate the pressure energy term, specifically asking for guidance on substituting pressure values, such as 100 kPa, into the equation.
  • One participant clarifies that the standard form of Bernoulli's equation includes a pressure term rather than a pressure energy term, and provides an example calculation for potential pressure energy based on volume and pressure values.
  • Another participant reiterates the need for clarity on calculating pressure energy, emphasizing the importance of using appropriate units for pressure.

Areas of Agreement / Disagreement

Participants generally agree on the need to understand how to calculate pressure energy, but there is no consensus on the specific formula or approach to use. Multiple competing views and interpretations of the Bernoulli equation remain present in the discussion.

Contextual Notes

Some participants express uncertainty regarding the conversion of pressure terms to energy and the appropriate values to substitute in calculations. There are also unresolved questions about the relationship between pressure, volume, and energy in the context of the Bernoulli equation.

malikengg
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In the Bernoulli equation, i know that velocity is in m/s and mass in N which gives energy in joules. Likewise potential energy id also in joules being mgh. In pressure energy what are the variants? i.e what is formula for calcualting the pressure energy term in the equation? If we compute everything in joules, then how the pressure energy would be calculated? i want to know formula for calculating the pressure energy term in the equation.
 
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malikengg said:
In the Bernoulli equation, i know that velocity is in m/s and mass in N which gives energy in joules. ...
The terms in Bernoulli's equation are stated as energy per unit volume. (Note that density is mass per unit volume). To convert these terms to energy terms, you need to multply by some amount of volume.
 
yeah, okay..but i wanted to know how to calculate the pressure energy term in the equation. e.g to calculate the kinetic energy, we used mass and velocity (m*v^2/2). Likewise how the pressure energy would be calculated. If we are given an initial value of pressure, say 100kPa (N/m^2), in some problem, what value to substitute in the equation?
 
malikengg said:
yeah, okay..but i wanted to know how to calculate the pressure energy term in the equation. e.g to calculate the kinetic energy, we used mass and velocity (m*v^2/2). Likewise how the pressure energy would be calculated. If we are given an initial value of pressure, say 100kPa (N/m^2), in some problem, what value to substitute in the equation?
The standard form of Bernoulli's equation includes a pressure term, not a pressure energy term. The velocity term is 1/2 density velocity2 (density as opposed to mass). You need to multiply the terms by some amount of volume to get energies.

So if there was 1 meter3 of gas at 1 Pa, then the potential pressure energy would be 1 (N/m2) (m3) = 1 N m = 1 joule. If there was 1 meter3 at 100 kPa, the potential pressure energy would be 100 kilo-joules.
 
malikengg said:
yeah, okay..but i wanted to know how to calculate the pressure energy term in the equation. e.g to calculate the kinetic energy, we used mass and velocity (m*v^2/2). Likewise how the pressure energy would be calculated. If we are given an initial value of pressure, say 100kPa (N/m^2), in some problem, what value to substitute in the equation?
Welcome to Physics Forums.

People seem to be missing what you are asking. If you are using kg, m, and s units, then use units of N/m^2 for pressure -- which is equivalent to 1 Pa.
 

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