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

[71GA]

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

 

[Andrew Mason]

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 $-(p_2-p_1)$. 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

 

[71GA]

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 :)

 

[lalbatros]

Ni treba, da rodil slovenski pisati v slovenščini, lahko samo uporabo Google prevod orodje.
See: http://translate.google.com/?hl=fr&ie=UTF8&text=&langpair=fr|en#en|sl|

 

[PJC01]

for reaching out! It's great that you're attempting to calculate Bernoulli's equation on your own. Negative pressures in Bernoulli's equation can be a bit confusing, but there are a few reasons why you may be getting them.

First, make sure that you are using the correct units for your calculations. Bernoulli's equation requires consistent units of pressure, velocity, and density. If your units are not consistent, you may end up with negative pressures.

Another common mistake is not taking into account the direction of the flow. Bernoulli's equation assumes that the flow is in the same direction throughout the entire system. If your calculations involve changes in flow direction, you may end up with negative pressures.

Additionally, negative pressures can also occur when there are losses or inefficiencies in the system. These losses can be caused by friction, turbulence, or other factors that decrease the energy of the fluid. In these cases, the pressure may become negative in order to balance out the energy loss.

I would recommend double-checking your calculations and units, as well as considering any changes in flow direction or potential losses in the system. If you're still getting negative pressures, it may be helpful to consult with a colleague or a textbook to ensure that your calculations are correct.

Keep up the good work and don't be discouraged by negative pressures. They can be a valuable indicator of potential issues in a system and can help guide further analysis and improvements. Good luck!