'''
In the previous exercise, you made the ball move over the screen, but the code 
was written in such a way that the ball moved from left to right, then stopped 
at the end of the graphical window. When simulating a less regulated movement 
of a ball, the path is less predictable or even unpredictable, so containing 
the ball inside the graphical window should be programmed in a different way. 

**Exercise A:**
The algorithm for bouncing is very simple: when the ball reaches the top or 
bottom border of the graphical window, change the sign of the displacement 
in vertical direction (`dY = -dY`). When the ball bounces to the left or right 
side of the window, change the sign of the horizontal displacement (`dX`). 
 
Write a Python program in which a ball moves in a diagonal line at constant 
speed and bounces when it reaches one of the borders of the graphical window. 
The ball should keep moving until the graphical window is closed. Try different 
angles of movement. 

**Exercise B:**
Extend your code from exercise A such that it simulates the bouncing of a ball 
in the presence of gravity: decrease the ball displacement in the vertical 
direction when the ball is moving upwards, and increase the ball displacement 
in the vertical direction when the ball is moving downwards by subtracting a 
small value from `dY` (e.g., `dY = dY - 0.1`). If the ball bounces higher each 
step, adjust the program so that the peaks are lower each time the ball bounces.
'''