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

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Old   June 5, 2003, 04:57
Default what does this unit,[kg m^-2 s^-2], mean?
  #1
Miko
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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
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Old   June 5, 2003, 09:41
Default Re: what does this unit,[kg m^-2 s^-2], mean?
  #2
bob
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Is it just the momentum per unit volume, as you are applying the source term to a subdomain volume ? Bob
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Old   June 5, 2003, 20:04
Default Re: what does this unit,[kg m^-2 s^-2], mean?
  #3
Miko
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Hi Bob!

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

Miko
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Old   June 6, 2003, 08:11
Default Re: what does this unit,[kg m^-2 s^-2], mean?
  #4
zahid
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Hi Miko It means Force per unit volume.
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Old   June 7, 2003, 09:25
Default Re: what does this unit,[kg m^-2 s^-2], mean?
  #5
Miko
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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
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Old   June 9, 2003, 09:14
Default Re: what does this unit,[kg m^-2 s^-2], mean?
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Bob
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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
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Old   June 9, 2003, 21:43
Default Re: what does this unit,[kg m^-2 s^-2], mean?
  #7
zahid
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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
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Old   June 12, 2003, 04:05
Default Re: what does this unit,[kg m^-2 s^-2], mean?
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Miko
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Yes, I agree with Zahid. In fact, momentum=force*time
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Old   August 18, 2003, 09:19
Default Re: what does this unit,[kg m^-2 s^-2], mean?
  #9
CFX 4.3 users
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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

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Old   September 1, 2003, 16:29
Default Re: what does this unit,[kg m^-2 s^-2], mean?
  #10
George
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it means temporary change of momentun per unit of volume, analyze it and you'll see.
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