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Tip revision: de50cdfcf9e3ba415fa09a3c9203d4d95a14e5b3 authored by Benjamin Peterson on 31 May 2014, 18:22:47 UTC
fix news header
fix news header
Tip revision: de50cdf
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()