Demo/turtle/tdemo_planet_and_moon.py

   1 #!/usr/bin/env python
   2 """       turtle-example-suite:
   3
   4         tdemo_planets_and_moon.py
   5
   6 Gravitational system simulation using the
   7 approximation method from Feynman-lectures,
   8 p.9-8, using turtlegraphics.
   9
  10 Example: heavy central body, light planet,
  11 very light moon!
  12 Planet has a circular orbit, moon a stable
  13 orbit around the planet.
  14
  15 You can hold the movement temporarily by pressing
  16 the left mouse button with mouse over the
  17 scrollbar of the canvas.
  18
  19 """
  20 from turtle import Shape, Turtle, mainloop, Vec2D as Vec
  21 from time import sleep
  22
  23 G = 8
  24
  25 class GravSys(object):
  26     def __init__(self):
  27         self.planets = []
  28         self.t = 0
  29         self.dt = 0.01
  30     def init(self):
  31         for p in self.planets:
  32             p.init()
  33     def start(self):
  34         for i in range(10000):
  35             self.t += self.dt
  36             for p in self.planets:
  37                 p.step()
  38
  39 class Star(Turtle):
  40     def __init__(self, m, x, v, gravSys, shape):
  41         Turtle.__init__(self, shape=shape)
  42         self.penup()
  43         self.m = m
  44         self.setpos(x)
  45         self.v = v
  46         gravSys.planets.append(self)
  47         self.gravSys = gravSys
  48         self.resizemode("user")
  49         self.pendown()
  50     def init(self):
  51         dt = self.gravSys.dt
  52         self.a = self.acc()
  53         self.v = self.v + 0.5*dt*self.a
  54     def acc(self):
  55         a = Vec(0,0)
  56         for planet in self.gravSys.planets:
  57             if planet != self:
  58                 v = planet.pos()-self.pos()
  59                 a += (G*planet.m/abs(v)**3)*v
  60         return a
  61     def step(self):
  62         dt = self.gravSys.dt
  63         self.setpos(self.pos() + dt*self.v)
  64         if self.gravSys.planets.index(self) != 0:
  65             self.setheading(self.towards(self.gravSys.planets[0]))
  66         self.a = self.acc()
  67         self.v = self.v + dt*self.a
  68
  69 ## create compound yellow/blue turtleshape for planets
  70
  71 def main():
  72     s = Turtle()
  73     s.reset()
  74     s.tracer(0,0)
  75     s.ht()
  76     s.pu()
  77     s.fd(6)
  78     s.lt(90)
  79     s.begin_poly()
  80     s.circle(6, 180)
  81     s.end_poly()
  82     m1 = s.get_poly()
  83     s.begin_poly()
  84     s.circle(6,180)
  85     s.end_poly()
  86     m2 = s.get_poly()
  87
  88     planetshape = Shape("compound")
  89     planetshape.addcomponent(m1,"orange")
  90     planetshape.addcomponent(m2,"blue")
  91     s.getscreen().register_shape("planet", planetshape)
  92     s.tracer(1,0)
  93
  94     ## setup gravitational system
  95     gs = GravSys()
  96     sun = Star(1000000, Vec(0,0), Vec(0,-2.5), gs, "circle")
  97     sun.color("yellow")
  98     sun.shapesize(1.8)
  99     sun.pu()
 100     earth = Star(12500, Vec(210,0), Vec(0,195), gs, "planet")
 101     earth.pencolor("green")
 102     earth.shapesize(0.8)
 103     moon = Star(1, Vec(220,0), Vec(0,295), gs, "planet")
 104     moon.pencolor("blue")
 105     moon.shapesize(0.5)
 106     gs.init()
 107     gs.start()
 108     return "Done!"
 109
 110 if __name__ == '__main__':
 111     msg = main()
 112     print msg
 113     mainloop()