| #!/usr/bin/env python3 |
| """ 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.getscreen().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.getscreen().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() |