| 33 | p.step() |
| 34 | |
| 35 | class Star(Turtle): |
| 36 | def __init__(self, m, x, v, gravSys, shape): |
| 37 | Turtle.__init__(self, shape=shape) |
| 38 | self.penup() |
| 39 | self.m = m |
| 40 | self.setpos(x) |
| 41 | self.v = v |
| 42 | gravSys.planets.append(self) |
| 43 | self.gravSys = gravSys |
| 44 | self.resizemode("user") |
| 45 | self.pendown() |
| 46 | def init(self): |
| 47 | dt = self.gravSys.dt |
| 48 | self.a = self.acc() |
| 49 | self.v = self.v + 0.5*dt*self.a |
| 50 | def acc(self): |
| 51 | a = Vec(0,0) |
| 52 | for planet in self.gravSys.planets: |
| 53 | if planet != self: |
| 54 | v = planet.pos()-self.pos() |
| 55 | a += (G*planet.m/abs(v)**3)*v |
| 56 | return a |
| 57 | def step(self): |
| 58 | dt = self.gravSys.dt |
| 59 | self.setpos(self.pos() + dt*self.v) |
| 60 | if self.gravSys.planets.index(self) != 0: |
| 61 | self.setheading(self.towards(self.gravSys.planets[0])) |
| 62 | self.a = self.acc() |
| 63 | self.v = self.v + dt*self.a |
| 64 | |
| 65 | ## create compound yellow/blue turtleshape for planets |
| 66 |
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