'Parabola.bas       2 Jun 2007
'par65100.bas  12 Jun 2007
'Robert Fritzius
'Shade Tree Physics
'This program calculates x any y positions for two gravitationally
'interacting bodies. Its arbitrary constants have been adjusted to
'produce a parabola-like curve for each interacting body.

    G=.004   'Gravitational Constant
    Xp=0     'X position object(1)
    Yp=0     'Y position object(1)
    Xc=1     'X position object(2)
    Yc=0     'Y position object(2)
    Mp=1     'Mass object(1)
    Mc=1     'Mass object(2)
    Vpx=0    'Vx object(1)
    Vpy=-.06 'Vy object(1)
    Vcx=0    'Vx object(2)
    Vcy=.06  'Vy object(2)
    t=0      'time
    dx=0     'delta x
    dy=0     'delty y
    Rsq=0    'Distance squared object(1) to (2)
    R=0      'Distance object(1) to (2)
    F=0      'Gravitational force 
    A$="##.##  ##.###  ###.###   ##.###  ###.###"

     LPrint "  t       Xp      Yp        Xc     Yc"
     lprint using A$;t;Xp;Yp;Xc;Yc

     for t=.1 to 6 step .1
      dx=Xc-Xp
      dy=Yc-Yp
      Rsq=(dx^2+dy^2)
      R=(Rsq)^.5
      F=G*Mc*Mp/Rsq
      Vpx=Vpx+F*dx/R
      Vpy=Vpy+F*dy/R
      Vcx=Vcx-F*dx/R
      Vcy=Vcy-F*dy/R
      Xp=Xp+Vpx
      Yp=Yp+Vpy
      Xc=Xc+Vcx
      Yc=Yc+Vcy
      lprint using A$;t;Xp;Yp;Xc;Yc
     next t
      lprint chr$(12)