diff --git a/ball.py b/ball.py
new file mode 100644
index 0000000..01277bc
--- /dev/null
+++ b/ball.py
@@ -0,0 +1,19 @@
+from element import Element
+from pygame import Surface
+
+class Ball(Element):
+    def __init__(self, surface: Surface, x: int, y: int, visible: bool = True) -> None:
+        super().__init__(surface, x, y, visible, False)
+        # this states whether the ball is released or not.
+        self.__is_released = False
+    def is_released(self) -> bool:
+        """
+        :return: whether the ball is released or not.
+        """
+        return self.__is_released
+    def set_released(self, released:bool) -> None:
+        """
+        Set the ball as released or not.
+        :param bool released: the release state of the ball.
+        """
+        self.__is_released = released
\ No newline at end of file
diff --git a/ball_release_event_listener.py b/ball_release_event_listener.py
index 48d8036..481bcc2 100644
--- a/ball_release_event_listener.py
+++ b/ball_release_event_listener.py
@@ -15,10 +15,14 @@ def run(self, event, game):
         # retrieve the placeholder ball.
         placeholder_ball = game.get_window().get_element("placeholder_ball")
         # check if the ball is at the same position
-        if abs(ball.get_x() - ball.get_initial_x()) < 15 and abs(ball.get_y() - ball.get_initial_y()) < 15:
+        if abs(ball.get_x() - ball.get_initial_x()) < 15 and abs(ball.get_y() - ball.get_initial_y()) < 15 or ball.is_released():
             return
+        ball.set_released(True)
         # disable ball.
         placeholder_ball.set_visible(False)
+        # clear dots.
+        for i in range(20):
+            game.get_window().remove_element(("dot_",str(i)))
         # launch new thread.
         self.__t = StoppableThread(target=self.__move_ball, args=(game,))
         # register the thread in order to be able to kill it.
diff --git a/drag_event_listener.py b/drag_event_listener.py
index 176c4ce..5a7e4c7 100644
--- a/drag_event_listener.py
+++ b/drag_event_listener.py
@@ -1,4 +1,5 @@
 from event_listener import EventListener
+from element import Element
 import pygame
 
 class DragEventListener(EventListener):
@@ -8,18 +9,27 @@ def __init__(self) -> None:
         self.__white_dot = pygame.transform.scale(self.__white_dot, (20, 20))
     
     def run(self, event, game):
-        if pygame.mouse.get_pressed()[0] == True:
-            # retrieve the ball.
-            ball = game.get_window().get_element("ball")
+        # pre-register the dots.
+        for i in range(0, 20):
+            game.get_window().register_element(("dot_",str(i)), Element(self.__white_dot, 0, 0, False, False))
+        # retrieve the ball.
+        ball = game.get_window().get_element("ball")
+        if pygame.mouse.get_pressed()[0] == True and not ball.is_released():
             # update x and y position.
             ball.set_x(pygame.mouse.get_pos()[0] - 30)
             ball.set_y(pygame.mouse.get_pos()[1] - 30)
             # get the initial x and y value.
             ix, iy = ball.get_initial_x(), ball.get_initial_y()
-            for t in range(0, 150):
-                t = t
+            vx, vy = 1.1 * (ix - ball.get_x()), 1.1 * (iy - ball.get_y())
+            for t in range(20):
                 # get the inital vector values.
-                vx, vy = ix - ball.get_x(), iy - ball.get_y()
-                x = ball.get_x() + 30 + vx * t
-                y = -(1/2) * -9.81 * t**2 + vy * t + ball.get_y() + 30
-                game.get_screen().blit(self.__white_dot, (x, y))
\ No newline at end of file
+                x = (ball.get_x() + 30 + vx * t)
+                y = (9.81 * t**2 + vy * t + ball.get_y() + 30)
+                if t != 0:
+                    # retrieve the dot.
+                    dot = game.get_window().get_element(("dot_",str(t)))
+                    # update x and y coordinates.
+                    dot.set_x(x)
+                    dot.set_y(y)
+                    # set the dot visible.
+                    dot.set_visible(True)
\ No newline at end of file
diff --git a/element.py b/element.py
index 3b1dd6f..b46c5d3 100644
--- a/element.py
+++ b/element.py
@@ -1,13 +1,14 @@
 from pygame import Surface
 
 class Element():
-    def __init__(self, surface:Surface, x:int, y:int, visible:bool=True) -> None:
+    def __init__(self, surface:Surface, x:int, y:int, visible:bool=True, allow_override:bool=False) -> None:
         self.__surface = surface
         # those are the inital x and y coordinates. (those coordinates are immutable)
         self.__ix, self.__iy = x, y
         # those are the mutable x and y coordinates.
         self.__x, self.__y = x, y
         self.__visible = visible
+        self.__allow_override = allow_override
         pass
     def get(self) -> tuple:
         """
@@ -44,6 +45,12 @@ def get_surface(self):
         :return: the element surface.
         """
         return self.__surface
+    def allow_override(self):
+        """
+        :return: whether the element can be overrident or not.
+        (another element can erase this one.)
+        """
+        return self.__allow_override
     def is_visible(self):
         """
         :return: whether the element is visible or not. (Note it can still interact.)
diff --git a/game.py b/game.py
index f1d86a7..5a51469 100644
--- a/game.py
+++ b/game.py
@@ -4,6 +4,7 @@
 from player import Player
 from element import Element
 from window import Window
+from ball import Ball
 
 from event_listener import EventListener
 from drag_event_listener import DragEventListener
@@ -31,7 +32,7 @@ def __init__(self, screen:pygame.Surface, img_location:str, img_name: str, sound
         # register the field without public.
         self.get_window().register_element("field", Element(field, 0, 0))
         # register the ball.
-        self.get_window().register_element("ball", Element(ball, 170, 450))
+        self.get_window().register_element("ball", Ball(ball, 170, 450))
         # register the placeholder ball.
         self.get_window().register_element("placeholder_ball", Element(placeholder_ball, 170, 450))
         # listen to events.
@@ -68,7 +69,7 @@ def setup(self):
             for element in self.__window.get_elements():
                 # retrive the object.
                 obj = element[1]
-                if(obj.is_visible()):
+                if obj != None and obj.is_visible():
                     self.__screen.blit(obj.get()[0], obj.get()[1])
             for event in pygame.event.get():
                 if event.type == pygame.QUIT:
diff --git a/window.py b/window.py
index d3ee42e..08a9a56 100644
--- a/window.py
+++ b/window.py
@@ -8,18 +8,34 @@ def register_element(self, key:str, element):
         :param str key: the key to pair to the given element.
         :param object element: the element to store.
         """
+        # try to get the previous element bind with this key.
+        previous_element = self.get_element(key)
+        # check if this element can be overriden.
+        if previous_element != None and previous_element.allow_override():
+            self.remove_element(key)
         self.__elements.append([key, element])
     def get_element(self, key:str):
         """
         If present returns the element paired with the given key
         else it raises RuntimeError.
         :param str key: the key paired to the game element.
-        :return: the game element.
+        :return: the game element or None if not found.
         """
         for element in self.__elements:
             if element[0] == key:
                 return element[1]
-        raise RuntimeError("element not found for key: ", key)
+        return None
+    def remove_element(self, key:str) -> bool:
+        """
+        Removes the element paired to the given key.
+        :param str key: the key bind with the element to remove.
+        :return: whether the element has been removed or not.
+        """
+        for element in self.__elements:
+            if element[0] == key:
+                self.__elements.remove(element)
+                return True
+        return False
     def get_elements(self):
         """
         :return: the game elements.