Science Forums Biology Forum Molecular Biology Forum Physics Chemistry Forum N-body problem

 Physics Forum Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

# N-body problem

## N-body problem - Physics Forum

### N-body problem - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

#1
12-01-2003, 04:33 AM
 Torstein Raanes Guest Posts: n/a
N-body problem

Hello

Abstract:
The N-body problem looks into solving the gravity effect on all
bodies in a system most effectively.

My problem:
To get to the solution, I have to calculate the center of gravity
in a given section of the problem area that will represent all
bodies as one. This will be solved in two dimensions. All
bodies have a mass, and a position with x, y coordinates.
Could someone help me with the formula to find this point? Also
the gravity force for this point would help (and I would imagine
it is necessary to find the solution.)

Regards,
Torstein Raanes
#2
12-01-2003, 10:31 AM
N-body problem

"Torstein Raanes" <[Only registered users see links. ].uit.no> wrote in message
news:bqega8\$2p5f\$[Only registered users see links. ].no...

In a Cartesian coordinate system, the coordinates of the center of mass of a
group of point masses is the *weighted* average of the coordinates of the
individual masses. In two dimensions:

X-bar = Sum[m(i)*x(i)]/Sum[m(i)]

and

Y-bar = Sum[m(i)*y(i)]/Sum[m(i)]

Again, outside the circumscribing sphere, the collection can be treated as a
single body with

m(tot) = Sum[m(i)]

The difficulty with the N-body problem is that there are more momenta to be
conserved than there are degrees of geometric freedom, so separation of
variables into orthonormal coordinates is not possible in general. In the
two-body problem we get a solution by transforming the x, y, and z
coordinates of two bodies into six *new* coordinates with orthogonal
momenta: the x, y, and z momenta of the center of mass and the r, theta, and
z momenta (cylindrical coordinates) of the rotating binary. With only three
bodies you get nine momenta to be conserved, and it is not easy to find
places in 3 dimensions to put 9 orthogonal momenta.

Sometimes a three body problem can "rearrange" itself into two two-body
problems by "ejecting" one body leaving the other two as a binary. Then the
ejected body and the binary become an effectively independent two-body
problem.

Tom Davidson
Richmond, VA

 Tags nbody , problem

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home General Science Forums     Biology Forum     New Member Introductions Forum     Chemistry Forum         Organic Chemistry Forum     Physics Forum     General Science Questions and Layperson Board         Science and Religion Forum         Zoology Forum     Environmental Sciences and Issues General Forum     Chit Chat         Science and Lab Jokes     Article Discussion     Molecular Biology News and Announcements         Conferences , Symposiums and Meetings         Molecular Station Suggestion Forum         Instructions for Posting, Help, and Frequently Asked Questions     Science News and Views         Molecular Biology Lectures and Videos     Science Careers         Post-doctoral         Medical School         Ph.D Doctor of Philosophy         Science Jobs Forum Molecular Research Topics Forum     PCR - Polymerase Chain Reaction Forum         Real-Time PCR and Quantitative PCR Forum     Bioinformatics         BioStatistics Forum     Molecular Biology Techniques         Molecular Cloning Forum         Electrophoretic Mobility Shift Assay Forum         Agarose Gel Electrophoresis Forum         BioPhysics Forum         Gene Therapy     Cell Biology and Cell Culture         Apoptosis, Autophagy, and Necrosis Forum         Flow Cytometry Forum         Transfection Forum         Confocal - Microscopy Imaging Techniques         Immunology and Host-Pathogen Interactions         Signalling Biology         Stem Cell Forum     Basic Lab Protocols and Techniques         SDS-PAGE Gel Electrophoresis Forum     DNA Techniques         DNA Extraction Forum         cDNA Forum     Epigenetics Forum: DNA Methylation, Histone and Chromatin Study         ChIP Chromatin Immunoprecipitation Forum     Protein Science         Antibody Forum             Immunoprecipitation Forum         Western Blot Forum         Protein Crystallography Forum         Recombinant Protein Forum         ELISA Assay Forum         Protein Forum     Proteomics Forum         Peptide Forum         Mass Spectrometry Forum         2-D Gel Electrophoresis Forum     Omics and Genomics Forum         Microarrays Forum         Genomics Forum     RNA Techniques Forum         RNAi and SiRNA Forum     Histology Forum         Immunohistochemistry Forum         Immunocytochemistry Forum         Electron Microscopy Forum         Immunofluorescence Forum     Protocols and Methods Forum     Molecular Biology Articles and Protocols     Animal and Molecular Model Systems         Drosophila Forum         Yeast Forum         Zebrafish Forum         Botany Forum         C Elegans Forum         Arabidopsis and Plant Biology         Microbiology Forum         Knockout Mouse Forum     Chromatography Forum Products and Vendor Discussion     Molecular Biology Products and Vendors         Bad Product/Service? Post Here         Lab Equipment Discussion and Reviews Regional Molecular Biology Discussion     Forum Chemie     Forum Biologie     Forum Biologia     Forum Chimica     Forum Physik     Forum De Chimie     Forum De Physique     Forum Chemia     中国人分子的生物学论坛 Chinese     Greek Molecular Biology Forums     分子生物学のフォーラム Japanese     ميدان فارسى. Persian Molecular Biology     [أربيك] علم ساحة- Arabic     Forum de Biologie Moleculaire     Forum Biologia Molecolare     Forum die Molekularbiologie     Foro Biologia Molecular

 Similar Threads Thread Thread Starter Forum Replies Last Post Steve Nothwehr Protocols and Methods Forum 2 10-16-2009 08:59 AM ggerard Western Blot Forum 3 12-22-2008 05:52 PM DougC Physics Forum 0 07-03-2008 08:49 PM Jan Gooral Physics Forum 0 05-22-2008 02:53 PM

All times are GMT. The time now is 06:40 PM.

 Contact Us - Molecular Biology - Archive - Privacy Statement - Top