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-   -   what does this unit,[kg m^-2 s^-2], mean? (https://www.cfd-online.com/Forums/cfx/19675-what-does-unit-kg-m-2-s-2-mean.html)

 Miko June 5, 2003 04:57

what does this unit,[kg m^-2 s^-2], mean?

Hi all! I creat a fluid sub-domain in CFX Build. When I press "Bulk Sources" and enable "Momentum Source", momentum along three direction can be found. I'm confused by the unit of the momentum, [kg m^-2 s^-2]. It also can't be changed into another one. Is anyone kind enough to let me know what it means?

Miko

 bob June 5, 2003 09:41

Re: what does this unit,[kg m^-2 s^-2], mean?

Is it just the momentum per unit volume, as you are applying the source term to a subdomain volume ? Bob

 Miko June 5, 2003 20:04

Re: what does this unit,[kg m^-2 s^-2], mean?

Hi Bob!

But if it means the momentum per unit volume, it should be [kg m^-2 s^-1}, I think.

Miko

 zahid June 6, 2003 08:11

Re: what does this unit,[kg m^-2 s^-2], mean?

Hi Miko It means Force per unit volume.

 Miko June 7, 2003 09:25

Re: what does this unit,[kg m^-2 s^-2], mean?

Thank you all! I think Zahid is right! [kg m^-2 s^-2] means force per uint volume, such as: (density)*(gravitational acceleration), (electric current density)*(magnetic field). Their dimensions are both equal to [kg m^-2 s^-2].

Miko

 Bob June 9, 2003 09:14

Re: what does this unit,[kg m^-2 s^-2], mean?

Hi Miko, yes you are right (or Zahid is), I was missing the seconds out. So would it be the same as saying Momentum per unit volume per second ? Bob

 zahid June 9, 2003 21:43

Re: what does this unit,[kg m^-2 s^-2], mean?

Hi Bob Yes you can say it rate of change of momentum per unit volume, and according to Newton's second law of motion it is equal to force per unit volume. Zahid

 Miko June 12, 2003 04:05

Re: what does this unit,[kg m^-2 s^-2], mean?

Yes, I agree with Zahid. In fact, momentum=force*time

 CFX 4.3 users August 18, 2003 09:19

Re: what does this unit,[kg m^-2 s^-2], mean?

most probably, it can be presure per unit length, cause, if you simplify the unit of pressure [F/A] it becomes kg/(m.s^2). check it out if my suggestion gives sound to what you are doing

bye

 George September 1, 2003 16:29

Re: what does this unit,[kg m^-2 s^-2], mean?

it means temporary change of momentun per unit of volume, analyze it and you'll see.

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