Bernoulli equation and velocity problem

[malikengg]

Main Question or Discussion Point

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.

 

[voko]

Have you seen this: http://en.wikipedia.org/wiki/Bernoulli's_principle ?

 

[rcgldr]

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.

 

[malikengg]

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?

 

[rcgldr]

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.

 

[Redbelly98]

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.