File Content: tdemo_planet_and_moon.py #! /usr/bin/env python """ turtle-example-suite: tdemo_planets_and_moon.py Gravitational system simulation using the approximation method from Feynman-lectures, p.9-8, using turtlegraphics. Example: heavy central body, light planet, very light moon! Planet has a circular orbit, moon a stable orbit around the planet. You can hold the movement temporarily by pressing the left mouse button with mouse over the scrollbar of the canvas. """ from turtle import Shape, Turtle, mainloop, Vec2D as Vec from time import sleep G = 8 class GravSys(object): def __init__(self): self.planets = [] self.t = 0 self.dt = 0.01 def init(self): for p in self.planets: p.init() def start(self): for i in range(10000): self.t += self.dt for p in self.planets: p.step() class Star(Turtle): def __init__(self, m, x, v, gravSys, shape): Turtle.__init__(self, shape=shape) self.penup() self.m = m self.setpos(x) self.v = v gravSys.planets.append(self) self.gravSys = gravSys self.resizemode("user") self.pendown() def init(self): dt = self.gravSys.dt self.a = self.acc() self.v = self.v + 0.5*dt*self.a def acc(self): a = Vec(0,0) for planet in self.gravSys.planets: if planet != self: v = planet.pos()-self.pos() a += (G*planet.m/abs(v)**3)*v return a def step(self): dt = self.gravSys.dt self.setpos(self.pos() + dt*self.v) if self.gravSys.planets.index(self) != 0: self.setheading(self.towards(self.gravSys.planets[0])) self.a = self.acc() self.v = self.v + dt*self.a ## create compound yellow/blue turtleshape for planets def main(): s = Turtle() s.reset() s.tracer(0,0) s.ht() s.pu() s.fd(6) s.lt(90) s.begin_poly() s.circle(6, 180) s.end_poly() m1 = s.get_poly() s.begin_poly() s.circle(6,180) s.end_poly() m2 = s.get_poly() planetshape = Shape("compound") planetshape.addcomponent(m1,"orange") planetshape.addcomponent(m2,"blue") s.getscreen().register_shape("planet", planetshape) s.tracer(1,0) ## setup gravitational system gs = GravSys() sun = Star(1000000, Vec(0,0), Vec(0,-2.5), gs, "circle") sun.color("yellow") sun.shapesize(1.8) sun.pu() earth = Star(12500, Vec(210,0), Vec(0,195), gs, "planet") earth.pencolor("green") earth.shapesize(0.8) moon = Star(1, Vec(220,0), Vec(0,295), gs, "planet") moon.pencolor("blue") moon.shapesize(0.5) gs.init() gs.start() return "Done!" if __name__ == '__main__': msg = main() print msg mainloop() Submit