diff --git a/src/doodles/__init__.py b/src/doodles/__init__.py
index e69de29..227f488 100644
--- a/src/doodles/__init__.py
+++ b/src/doodles/__init__.py
@@ -0,0 +1,6 @@
+from .doodles import Doodle, Group
+from .lines import Line
+from .shapes import Circle, Rectangle
+from .color import Color
+
+__all__ = [Doodle, Group, Line, Circle, Rectangle, Color]
diff --git a/src/doodles/doodles.py b/src/doodles/doodles.py
index c1720e7..6779c0e 100644
--- a/src/doodles/doodles.py
+++ b/src/doodles/doodles.py
@@ -1,7 +1,5 @@
 import random
 import copy
-import math
-import pygame
 from abc import ABC, abstractmethod
 from .color import Color
 from .world import world
@@ -171,94 +169,6 @@ class Doodle(ABC):
         return self.x, self.y
 
 
-class Line(Doodle):
-    def __init__(self, parent=None):
-        """
-        We keep the same interface as Doodle, to follow the Liskov substitution
-        principle.
-
-        We could add more *optional* arguments, but no more required ones
-        than the parent class.
-        """
-        super().__init__(parent)
-        # a line is stored as a position (on the parent class)
-        # and an offset vector
-        self._offset_vec = (10, 0)
-
-    def __repr__(self):
-        return f"Line(pos={self.pos_vec}, end={self.end_vec}, {self._color})"
-
-    def draw(self, screen):
-        """
-        Implementation of the abstract draw function for the line.
-
-        Note: This is a classic violation of single responsibility.
-
-        Instead, you could imagine a class like:
-
-        class DrawingBackend:
-            def draw_doodle(doodle_type, doodle): ...
-
-        class PygameBackend(DrawingBackend):
-            def draw_line(...): ...
-
-        This would make it possible to attach different
-        drawing backends, restoring single-responsibility
-        to the class and gaining flexibility from separating
-        presentation logic from data manipulation.
-        """
-        pygame.draw.line(screen, self._color, self.pos_vec, self.end_vec)
-
-    def to(self, x: float, y: float) -> "Doodle":
-        """
-        A setter for the line's offset vector.
-
-        Example usage:
-
-        Line().pos(10, 10).to(50, 50)
-
-        Makes a line from (10, 10) to (50, 50).
-        """
-        self._offset_vec = (x, y)
-        return self
-
-    def vec(self, degrees: float, magnitude: float):
-        """
-        Alternate constructor, to create offset vector from angle & length.
-        """
-        return self.to(
-            magnitude * math.cos(math.radians(degrees)),
-            magnitude * math.sin(math.radians(degrees)),
-        )
-
-    def random(self) -> "Doodle":
-        """
-        Overrides the parent's random, by extending the behavior.
-
-        This is an example of the open/closed principle.
-        We aren't modifying the parent classes' random function
-        since doing so would be fragile and break if the
-        parent class added more options.
-
-        Instead we just call it, and extend it with additional
-        randomization.
-        """
-        super().random()
-        magnitude = random.random() * 100
-        degrees = random.random() * 360
-        return self.vec(degrees, magnitude)
-
-    @property
-    def end_vec(self):
-        """
-        Parallel to pos_vec for end of line.
-        """
-        return (
-            self.x + self._offset_vec[0],
-            self.y + self._offset_vec[1],
-        )
-
-
 class Group(Doodle):
     """
     For now, only Group objects can have child doodles.
@@ -345,85 +255,3 @@ class Group(Doodle):
         # if we understand the implications of tightly
         # binding the implementations of these two classes.
         return self
-
-
-class Circle(Doodle):
-    def __init__(self, parent=None):
-        """
-        This is a less interesting class than Line, but very similar.
-        """
-        super().__init__(parent)
-        # circle is a position & radius
-        self._radius = 0
-
-    def __repr__(self):
-        return f"Circle(pos={self.pos_vec}, radius={self._radius}, {self._color}, parent={self._parent}))"
-
-    def draw(self, screen):
-        pygame.draw.circle(screen, self._color, self.pos_vec, self._radius)
-
-    def radius(self, r: float) -> "Doodle":
-        """
-        A setter for the circle's radius.
-        """
-        self._radius = r
-        return self
-
-    def grow(self, by: float):
-        """
-        Modify radius by an amount. (Negative to shrink.)
-        """
-        return self.radius(self._radius + by)
-
-    def random(self) -> "Doodle":
-        super().random()
-        # constrain to 10-100
-        return self.radius(random.random()*90 + 10)
-
-
-class Rectangle(Doodle):
-    def __init__(self, parent=None):
-        """
-        For compatibility with circle, the rectangle is centered at pos
-        and expands out width/2, height/2 in each cardinal direction.
-        """
-        super().__init__(parent)
-        self._width = 100
-        self._height = 100
-
-    def __repr__(self):
-        return f"Rect(pos={self.pos_vec}, width={self._width}, height={self._height}, parent={self._parent})"
-
-    def draw(self, screen):
-        rect = pygame.Rect(
-            self.x - self._width/2,
-            self.y - self._height/2,
-            self._width,
-            self._height,
-        )
-        pygame.draw.rect(screen, self._color, rect)
-
-    def width(self, w: float) -> "Doodle":
-        """
-        A setter for the width
-        """
-        self._width = w
-        return self
-
-    def height(self, h: float) -> "Doodle":
-        """
-        A setter for the height
-        """
-        self._height = h
-        return self
-
-    def grow(self, dw: float, dh: float):
-        """
-        Modify radius by an amount. (Negative to shrink.)
-        """
-        return self.width(self._w + dw).height(self._h + dh)
-
-    def random(self, upper=100) -> "Doodle":
-        super().random()
-        # constrain to 10-100
-        return self.width(random.random()*upper + 10).height(random.random()*upper + 10)
diff --git a/src/doodles/examples/balls.py b/src/doodles/examples/balls.py
index 35b1000..464e594 100644
--- a/src/doodles/examples/balls.py
+++ b/src/doodles/examples/balls.py
@@ -1,4 +1,4 @@
-from doodles.doodles import Group, Circle, Color
+from doodles import Circle, Color
 import random
 from doodles.world import world
 
@@ -17,7 +17,7 @@ Objects without an update method are static.
 class Ball(Circle):
     def __init__(self):
         super().__init__()
-        self.speed = 0.005 + random.random() * 0.005
+        self.speed = 9 + random.random() * 5
 
     def update(self):
         self.move(0, self.speed)
@@ -29,8 +29,8 @@ class Ball(Circle):
 class GravityBall(Circle):
     def __init__(self):
         super().__init__()
-        self.accel = 0.0000001 # accel per frame
-        self.speed = random.random() * 0.002
+        self.accel = 0.5 # accel per frame
+        self.speed = random.random() * 10
 
     def update(self):
         self.speed += self.accel
@@ -40,5 +40,5 @@ class GravityBall(Circle):
             self.pos(self.x, world.HEIGHT - 10.01)
 
 def create():
-    balls = [Ball().pos(40*i, 0).radius(10).color(Color.BLUE) for i in range(21)]
-    grav = [GravityBall().pos(20+40*i, 0).radius(10).color(Color.PURPLE) for i in range(21)]
+    [Ball().pos(40*i, 0).radius(10).color(Color.BLUE) for i in range(21)]
+    [GravityBall().pos(20+40*i, 0).radius(10).color(Color.PURPLE) for i in range(21)]
diff --git a/src/doodles/examples/circles.py b/src/doodles/examples/circles.py
index 0c059ba..681f67f 100644
--- a/src/doodles/examples/circles.py
+++ b/src/doodles/examples/circles.py
@@ -1,9 +1,15 @@
-from doodles.doodles import Group, Circle, Color
-from doodles.world import world
+from doodles import Group, Circle, Color
+
+def color_cycle():
+    while True:
+        yield Color.RED
+        yield Color.ORANGE
+        yield Color.YELLOW
 
 def create():
+    color = color_cycle()
     g = Group().pos(400, 300)
-    for r in range(20, 50, 5):
-        Circle(g).radius(r).color(Color.random()).z_index(-r)
-    for r in range(60, 150, 10):
-        Circle(g).radius(r).color(Color.random()).z_index(-r)
+    for r in range(20, 100, 12):
+        Circle(g).radius(r).color(next(color)).z_index(-r)
+    for r in range(100, 250, 12):
+        Circle(g).radius(r).color(next(color)).z_index(-r)
diff --git a/src/doodles/examples/copies.py b/src/doodles/examples/copies.py
index 28a8b46..36d7612 100644
--- a/src/doodles/examples/copies.py
+++ b/src/doodles/examples/copies.py
@@ -1,4 +1,4 @@
-from doodles.doodles import Group, Line, Circle, Color
+from doodles import Group, Circle, Color
 
 def original():
     g = Group()
diff --git a/src/doodles/examples/grid.py b/src/doodles/examples/grid.py
index 6f7cd10..9d415d3 100644
--- a/src/doodles/examples/grid.py
+++ b/src/doodles/examples/grid.py
@@ -1,14 +1,16 @@
-from doodles.doodles import Group, Line
+from doodles import Group, Line
 from doodles.layouts import make_grid
+import random
 
-def same_spiral():
+def spirals():
     while True:
         # Create a group of lines all with same origin, different angles.
         g = Group()
         for d in range(0, 180, 10):
-            Line(g).vec(d, 200 - d)
+            if random.random() > 0.1:
+                Line(g).vec(d, 200 - d)
         yield g
 
 def create():
     # Make copies, moving each one and modifying the color
-    make_grid(same_spiral(), 3, 4, 250, 140, x_offset=70, y_offset=20)
+    make_grid(spirals(), 3, 4, 250, 140, x_offset=70, y_offset=20)
diff --git a/src/doodles/examples/rects.py b/src/doodles/examples/rects.py
index eb9c169..b3e0c9b 100644
--- a/src/doodles/examples/rects.py
+++ b/src/doodles/examples/rects.py
@@ -1,5 +1,5 @@
-from doodles.doodles import Group, Rectangle, Color
+from doodles import Rectangle
 
 def create():
     for _ in range(100):
-        r = Rectangle().random(250)
+        Rectangle().random(250)
diff --git a/src/doodles/lines.py b/src/doodles/lines.py
new file mode 100644
index 0000000..d22d802
--- /dev/null
+++ b/src/doodles/lines.py
@@ -0,0 +1,92 @@
+import math
+import random
+import pygame
+from .doodles import Doodle
+
+class Line(Doodle):
+    def __init__(self, parent=None):
+        """
+        We keep the same interface as Doodle, to follow the Liskov substitution
+        principle.
+
+        We could add more *optional* arguments, but no more required ones
+        than the parent class.
+        """
+        super().__init__(parent)
+        # a line is stored as a position (on the parent class)
+        # and an offset vector
+        self._offset_vec = (10, 0)
+
+    def __repr__(self):
+        return f"Line(pos={self.pos_vec}, end={self.end_vec}, {self._color})"
+
+    def draw(self, screen):
+        """
+        Implementation of the abstract draw function for the line.
+
+        Note: This is a classic violation of single responsibility.
+
+        Instead, you could imagine a class like:
+
+        class DrawingBackend:
+            def draw_doodle(doodle_type, doodle): ...
+
+        class PygameBackend(DrawingBackend):
+            def draw_line(...): ...
+
+        This would make it possible to attach different
+        drawing backends, restoring single-responsibility
+        to the class and gaining flexibility from separating
+        presentation logic from data manipulation.
+        """
+        pygame.draw.aaline(screen, self._color, self.pos_vec, self.end_vec)
+
+    def to(self, x: float, y: float) -> "Doodle":
+        """
+        A setter for the line's offset vector.
+
+        Example usage:
+
+        Line().pos(10, 10).to(50, 50)
+
+        Makes a line from (10, 10) to (50, 50).
+        """
+        self._offset_vec = (x, y)
+        return self
+
+    def vec(self, degrees: float, magnitude: float):
+        """
+        Alternate constructor, to create offset vector from angle & length.
+        """
+        return self.to(
+            magnitude * math.cos(math.radians(degrees)),
+            magnitude * math.sin(math.radians(degrees)),
+        )
+
+    def random(self) -> "Doodle":
+        """
+        Overrides the parent's random, by extending the behavior.
+
+        This is an example of the open/closed principle.
+        We aren't modifying the parent classes' random function
+        since doing so would be fragile and break if the
+        parent class added more options.
+
+        Instead we just call it, and extend it with additional
+        randomization.
+        """
+        super().random()
+        magnitude = random.random() * 100
+        degrees = random.random() * 360
+        return self.vec(degrees, magnitude)
+
+    @property
+    def end_vec(self):
+        """
+        Parallel to pos_vec for end of line.
+        """
+        return (
+            self.x + self._offset_vec[0],
+            self.y + self._offset_vec[1],
+        )
+
diff --git a/src/doodles/main.py b/src/doodles/main.py
index 69cde13..52d734e 100644
--- a/src/doodles/main.py
+++ b/src/doodles/main.py
@@ -44,7 +44,8 @@ def main(modname: str = None):
     else:
         load_module(examples[ex_index])
 
-    elapsed = last_update = 0
+    elapsed = 0
+    clock = pygame.time.Clock()
 
     while True:
         for event in pygame.event.get():
@@ -58,11 +59,12 @@ def main(modname: str = None):
                 elif event.key == pygame.K_LEFT:
                     ex_index = (ex_index - 1) % len(examples)
                     load_module(examples[ex_index])
-        elapsed = pygame.time.get_ticks() - last_update
+        elapsed += clock.tick(FPS)
         while elapsed > MS_PER_FRAME:
             elapsed -= MS_PER_FRAME
             world.tick()
         world.render()
+        #print(clock.get_fps())
         pygame.display.flip()
 
 
diff --git a/src/doodles/shapes.py b/src/doodles/shapes.py
new file mode 100644
index 0000000..7f2407b
--- /dev/null
+++ b/src/doodles/shapes.py
@@ -0,0 +1,87 @@
+import random
+import pygame
+from .doodles import Doodle
+
+
+class Circle(Doodle):
+    def __init__(self, parent=None):
+        """
+        This is a less interesting class than Line, but very similar.
+        """
+        super().__init__(parent)
+        # circle is a position & radius
+        self._radius = 0
+
+    def __repr__(self):
+        return f"Circle(pos={self.pos_vec}, radius={self._radius}, {self._color}, parent={self._parent}))"
+
+    def draw(self, screen):
+        pygame.draw.circle(screen, self._color, self.pos_vec, self._radius)
+
+    def radius(self, r: float) -> "Doodle":
+        """
+        A setter for the circle's radius.
+        """
+        self._radius = r
+        return self
+
+    def grow(self, by: float):
+        """
+        Modify radius by an amount. (Negative to shrink.)
+        """
+        return self.radius(self._radius + by)
+
+    def random(self) -> "Doodle":
+        super().random()
+        # constrain to 10-100
+        return self.radius(random.random() * 90 + 10)
+
+
+class Rectangle(Doodle):
+    def __init__(self, parent=None):
+        """
+        For compatibility with circle, the rectangle is centered at pos
+        and expands out width/2, height/2 in each cardinal direction.
+        """
+        super().__init__(parent)
+        self._width = 100
+        self._height = 100
+
+    def __repr__(self):
+        return f"Rect(pos={self.pos_vec}, width={self._width}, height={self._height}, parent={self._parent})"
+
+    def draw(self, screen):
+        rect = pygame.Rect(
+            self.x - self._width / 2,
+            self.y - self._height / 2,
+            self._width,
+            self._height,
+        )
+        pygame.draw.rect(screen, self._color, rect)
+
+    def width(self, w: float) -> "Doodle":
+        """
+        A setter for the width
+        """
+        self._width = w
+        return self
+
+    def height(self, h: float) -> "Doodle":
+        """
+        A setter for the height
+        """
+        self._height = h
+        return self
+
+    def grow(self, dw: float, dh: float):
+        """
+        Modify radius by an amount. (Negative to shrink.)
+        """
+        return self.width(self._w + dw).height(self._h + dh)
+
+    def random(self, upper=100) -> "Doodle":
+        super().random()
+        # constrain to 10-100
+        return self.width(random.random() * upper + 10).height(
+            random.random() * upper + 10
+        )