112 lines
2.8 KiB
Python
112 lines
2.8 KiB
Python
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#!/usr/bin/env python3
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""" turtle-example-suite:
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tdemo_planets_and_moon.py
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Gravitational system simulation using the
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approximation method from Feynman-lectures,
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p.9-8, using turtlegraphics.
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Example: heavy central body, light planet,
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very light moon!
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Planet has a circular orbit, moon a stable
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orbit around the planet.
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You can hold the movement temporarily by
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pressing the left mouse button with the
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mouse over the scrollbar of the canvas.
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"""
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from turtle import Shape, Turtle, mainloop, Vec2D as Vec
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G = 8
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class GravSys(object):
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def __init__(self):
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self.planets = []
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self.t = 0
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self.dt = 0.01
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def init(self):
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for p in self.planets:
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p.init()
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def start(self):
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for i in range(10000):
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self.t += self.dt
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for p in self.planets:
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p.step()
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class Star(Turtle):
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def __init__(self, m, x, v, gravSys, shape):
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Turtle.__init__(self, shape=shape)
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self.penup()
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self.m = m
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self.setpos(x)
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self.v = v
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gravSys.planets.append(self)
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self.gravSys = gravSys
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self.resizemode("user")
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self.pendown()
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def init(self):
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dt = self.gravSys.dt
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self.a = self.acc()
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self.v = self.v + 0.5*dt*self.a
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def acc(self):
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a = Vec(0,0)
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for planet in self.gravSys.planets:
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if planet != self:
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v = planet.pos()-self.pos()
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a += (G*planet.m/abs(v)**3)*v
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return a
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def step(self):
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dt = self.gravSys.dt
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self.setpos(self.pos() + dt*self.v)
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if self.gravSys.planets.index(self) != 0:
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self.setheading(self.towards(self.gravSys.planets[0]))
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self.a = self.acc()
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self.v = self.v + dt*self.a
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## create compound yellow/blue turtleshape for planets
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def main():
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s = Turtle()
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s.reset()
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s.getscreen().tracer(0,0)
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s.ht()
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s.pu()
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s.fd(6)
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s.lt(90)
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s.begin_poly()
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s.circle(6, 180)
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s.end_poly()
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m1 = s.get_poly()
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s.begin_poly()
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s.circle(6,180)
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s.end_poly()
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m2 = s.get_poly()
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planetshape = Shape("compound")
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planetshape.addcomponent(m1,"orange")
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planetshape.addcomponent(m2,"blue")
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s.getscreen().register_shape("planet", planetshape)
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s.getscreen().tracer(1,0)
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## setup gravitational system
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gs = GravSys()
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sun = Star(1000000, Vec(0,0), Vec(0,-2.5), gs, "circle")
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sun.color("yellow")
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sun.shapesize(1.8)
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sun.pu()
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earth = Star(12500, Vec(210,0), Vec(0,195), gs, "planet")
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earth.pencolor("green")
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earth.shapesize(0.8)
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moon = Star(1, Vec(220,0), Vec(0,295), gs, "planet")
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moon.pencolor("blue")
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moon.shapesize(0.5)
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gs.init()
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gs.start()
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return "Done!"
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if __name__ == '__main__':
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main()
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mainloop()
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