IN PYTHON CHAPTER: ADVANCED GUI PROGRAMMING USING TKINTER Add two buttons--faster and slower to speed up or slow down the ball movement. See screenshot below for an example interface. Feel free to adjust by how much you want to increase/decrease the speed. *11.21 (Bouncing balls) Revise Listing 11.9 to add two buttons-Faster and Slower, as shown in Figure 11.28 - to speed up or slow down the ball movements. Figure 11.28 Two buttons are added to control the ball speed..