Why am I getting negative pressures when calculating Bernoulli's equation?

  • Context: Undergrad 
  • Thread starter Thread starter 71GA
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Discussion Overview

The discussion revolves around the application of Bernoulli's equation, specifically addressing the issue of obtaining negative pressures in calculations. Participants explore the derivation and potential errors in the application of the equation, with some contributions in Slovenian.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant reports obtaining negative pressures when calculating Bernoulli's equation and seeks assistance in identifying the error.
  • Another participant suggests that the derivation may be correct but indicates a possible sign error in the equation, specifically mentioning that the left side should be -(p_2-p_1).
  • There is a mention of the language barrier, as the original post was written in Slovenian, which may complicate understanding for some participants.
  • A participant expresses appreciation for the community's response and mentions their positive experience with the forum.
  • Another participant offers a suggestion for using translation tools to facilitate communication in different languages.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the cause of the negative pressures, as there are differing views on the correctness of the derivation and the interpretation of the signs in the equation.

Contextual Notes

The discussion includes references to language barriers and potential misinterpretations due to translation issues, which may affect the clarity of the technical arguments presented.

71GA
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Hello i tried to calculate Bernulli's equation myself and i get negative pressures on both sides of equation. What am i doing wrong? It is all in a document.

Ty
 

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71GA said:
Hello i tried to calculate Bernulli's equation myself and i get negative pressures on both sides of equation. What am i doing wrong? It is all in a document.

Ty
First of all you are writing it out in Slovenian. That makes it a little difficult for most people to follow.

But it appears that you have done the derivation correctly except you have a sign switched. The left side of your equation third from the bottom of page 1 should be [itex]-(p_2-p_1)[/itex]. This is because the change in PV is equal and opposite to the changes in kinetic and potential energy: eg. A decrease in PV energy must be equal to the increase in the sum of changes in kinetic and potential energies.

oh, in mimogrede, dobrodošli v fiziki forumih

AM
 
Nice to see someone here also talks Slovenian :) And thank you. This was my first thread on this forum and i got a nice reply. That is why i now like this forum :)
 

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