aUCBLogo Demos and Tests / testplunger

to testplunger
   setUpdateGraph false
   clearScreen
   PenUp
   r=200
   w=360
   a=50
   forever
   [   for [t 0 1 0.001]
      [   clearScreen
         Home
         setHeading w*t
         PenDown
         setPenColor HSB w 1 1
         forward a
         p=Pos
         x0=p.1
         y0=p.2
         y=(sqrt (sqr r)-(sqr x0))+y0
         setXY 0 y
         setHeading 0
         PenUp
         dx0_dt= a*w*cos w*t
         dy0_dt=-a*w*sin w*t
         v=1/(sqrt (sqr r)-(sqr x0))*x0*dx0_dt+dy0_dt
;pr v
         setXY 200 v/100
         updateGraph
         if Key? [break]
      ]
      if Key? [break]
   ]
end