title: Can't draw parabolic curve correctly with turtle graphics
body: <p>I'm making a game like 'angry bird'.</p>
  
  <p>There are two input:power and angle.
  I apply those inputs to parabolic curve.</p>
  
  <p>My turtle flies, making a parabolic curve. and my turtle have to hit the target,
  but my turtle draws strange curve when angle is greater than 46, angle is 30, 40 etc...</p>
  
  <p>I don't know where is problem....here is my code:</p>
  
  <pre><code>import turtle
  import random
  import math
  
  g=9.80665
  origin_x=-480
  origin_y=-180
  flag=False
  
  
  def create_target():
  
      x=random.randint(0,500)
      y=random.randint(-200,0)
      target=turtle.Turtle()
      target.hideturtle()
      target.penup()
      target.goto(x,y)
      target.shape('square')
      target.color('red')
      target.showturtle()
      return target
  
  def create_turtle():
  
      homework=turtle.Turtle()
      homework.hideturtle()
      homework.penup()
      homework.speed(0)
      homework.goto(origin_x,origin_y)
      homework.pendown()
      homework.shape('turtle')
      homework.color('blue')
      homework.left(45)
      homework.showturtle()
      return homework
  
  def setting():
      '''drawing back ground lines'''
      setting=turtle.Turtle()
      setting.hideturtle()
      setting.speed(0)
      turtle.colormode(255)
      setting.pencolor(214,214,214)
  
      for y in range(100,-101,-100):
          setting.penup()
          setting.goto(-500,y)
          setting.pendown()
          setting.goto(500,y)
  
      for x in range(-375,500,125):
          setting.penup()
          setting.goto(x,200)
          setting.pendown()
          setting.goto(x,-200)
  
  
  def throw_turtle(turtle,target):
      angle=int(input("Enter Angle:"))
      power=int(input("Enter Power:"))
      '''
      parabola fomula:
          x coordinate: speed(in here, that is power) * cos(anlge)*time
          y coordinate: speed*sin(angle)*time - (gravity speed*time**2)/2
      '''
      for time in range(1,20):
          # the origin fomula is for the situation that starts from (0,0). so I think
          # I should  compensate it, but is it right?
          x=power*math.cos(angle)*time + origin_x
          y=power*math.sin(angle)*time - (((time**2)*g)/2) + origin_y
          if x&lt;origin_x:  # I think it has problem...
              x-=origin_x
  
          turtle.goto(x,y)
          turtle.stamp()    #this is for testing
          if (x==target.xcor()) and (y==target.ycor()):
              print("******Target is HIT!!! ******")
              print("End of Game")
              flag=True
              break
      else:
          print("You missed...")
  
  
  turtle.setup(1000,400)
  windo=turtle.Screen()
  windo.title('Angry Turtle')
  setting()
  
  #__main
  
  my_turtle=create_turtle()
  while flag==False:
      target=create_target()
      my_turtle=create_turtle()
      my_turtle.speed(6)
  
      throw_turtle(my_turtle,target)
      my_turtle.hideturtle()
      target.hideturtle()
  </code></pre>
  
  <p>I think <code>create_target()</code> and <code>create_turtle()</code>, and <code>setting()</code> don't have problem...</p>