NOTES.txt

Run the file in python console with:

import bpy  
import os  
  
filename = os.path.join(os.path.dirname(bpy.data.filepath), "CalculateMomentumPaths.py")  
exec(compile(open(filename).read(), filename, 'exec'))

Panel is on the 'Tools Misc' tab.

Setup
    Create a system of objects (Could be a mixture of armature bones and regular objects)
    Add a mass object to represent the center of mass for each of these objects. Place the
    mass object at the center of mass of each bone/object and parent it to that object.
    Give each mass object a custom property ("mass")
    Put the objects in a group
    Groups will be listed on misc panel
    For groups that are systems of masses check the "isSystem" box
    Click enable momentum trail button
    Set the range "before" and "after"
    Click "Update Step 1"
    Click "OK" on the dialog that pops up
    Click "Update Step 2"
    Momentum paths should be visible in the scene