;;;;; SUMMARY
;; A single table-tennis ball drops.
;;;; 
;;  Copyright (C) 2005 James Steiner
;;  License: Creative Commons 2.0 at-sa-nc
;;
;;
;;;;
globals
[ ticks
  friction ;; portion of x-velocity that is lost at impact
  elastic  ;; portion of y-velocity that is retained at impact
  
]
breeds
[ balls
]
balls-own
[ xx yy xv yv
]
patches-own
[ ref-angle 
]

to startup
   setup
end

to setup
   ca
   let threedshapes [ "default" "circle" "dot" "square" "triangle" "cylinder" "line" "line-half" "car" ]
   set-default-shape balls "circle"
   set ticks 0
   ask patches [ set pcolor 1 + random-float 1 ]
   ask patches with [ pycor = (- screen-edge-y ) ] [ set pcolor blue - 4 + random-float 2 ]

   cct-balls 1
   [ set color white 
     set xx sex-1/2 * drop-point
     set yy ( sey-1/2 * fall-height )
     set xv initial-x-velocity * movement-scale
     set yv 0
     setxy xx yy
     ifelse show-path? [ pd ] [ pu ]
     if stop-motion? [ stamp ]
    ]
    set friction .05
    set elastic .8
end

to drop
   let stop? false
   set ticks ticks + 1
   ask balls
   [
     set yv yv - gravity * movement-scale
     ;; still on screen, or need to bounce?
     set yy yy + yv * movement-scale
     if yy < (-sey+1/2)
     [ ;; bounce
       set yy yy - yv
       let above-surface (sey-1/2 + yy) ;; 7 + -5  = 2
       let intercept-ratio -1 * above-surface / yv ;; -1 * 2 / (- 4) = .5
       let y-intercept xx + (intercept-ratio * xv)
       setxy y-intercept -sey+1/2
       set yv yv * elastic  * -1
       set xv xv * (1 - friction)
       set yy -sey+1/2 + yv * intercept-ratio * movement-scale
     ]
     ;; bounce (or roll) off screen?
     ifelse abs(xx + xv) > sex-1/2
     [ set xv (- xv) ]
     [ set xx xx + xv ]
     setxy xx yy
     if xv != 0 or yv != 0 [ set heading atan xv (-1 * abs yv) ]
     if stop-motion? and (ticks mod shutter-delay = 0 ) [ stamp ]
   ]
   if stop? [ stop ]
end

to-report sex-1/2 report screen-edge-x - .5 end
to-report sey-1/2 report screen-edge-y - .5 end
to-report -sex+1/2 report (- screen-edge-x) + .5 end
to-report -sey+1/2 report (- screen-edge-y) + .5 end
@#$#@#$#@
GRAPHICS-WINDOW
260
12
690
463
17
17
12.0
1
10
1
1
1
0
1
1
1

CC-WINDOW
5
477
699
572
Command Center
0

BUTTON
42
335
105
368
NIL
setup
NIL
1
T
OBSERVER
T
NIL

BUTTON
133
335
196
368
NIL
drop
T
1
T
OBSERVER
T
NIL

SLIDER
16
86
188
119
fall-height
fall-height
0
1
1.0
0.01
1
NIL

SLIDER
16
52
188
85
initial-x-velocity
initial-x-velocity
0
1
1.0
0.01
1
NIL

SWITCH
17
239
128
272
show-path?
show-path?
0
1
-1000

SWITCH
17
274
128
307
stop-motion?
stop-motion?
0
1
-1000

SLIDER
130
274
234
307
shutter-delay
shutter-delay
1
200
30
1
1
NIL

SLIDER
16
131
188
164
gravity
gravity
0.01
1
0.96
0.01
1
NIL

SLIDER
16
16
218
49
drop-point
drop-point
-1
1
-1.0
0.5
1
* screen-edge-x

BUTTON
194
131
249
164
earth
set gravity .96
NIL
1
T
OBSERVER
T
NIL

SLIDER
16
182
188
215
movement-scale
movement-scale
0.01
1
0.05
0.01
1
NIL

@#$#@#$#@
Gravity Demo by James Steiner
This model demonstrates some of the new features in NetLogo 3.
@#$#@#$#@
default
true
0
Polygon -7500403 true true 150 5 40 250 150 205 260 250

circle
false
0
Circle -7500403 true true -1 -1 301

line
true
0
Rectangle -7500403 true true 180 0 210 315
Rectangle -1 true false 150 -150 165 150
Rectangle -1 true false 150 150 165 450

mirror
true
0
Rectangle -7500403 true true 180 0 210 315
Rectangle -1 true false 150 -150 165 150
Rectangle -1 true false 150 150 165 450

@#$#@#$#@
NetLogo 3.0.2
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