Ok... had a look at your bouncing ball exercises. They're looking good (seconding the distracting watermark though).
Also... I kept an eye out for this but couldn't seem to see it in your animations (sorry if I just overlooked it), the frame before the ball hits the ground, stretch it vertically so that the top of the ball is moving the 'correct' distance from one frame to the next, but you've actaully stretched the ball downwards so it's touching the floor before it should.
Might sound strange, but what it does is it creates more of a change in shape, so you've got a tall stretched ball touching the ground in one frame, then the next frame is the squashed stout ball after. It makes the bounce feel more elastic and energetic... Would be happy to do a quick sketch up at home if you like... and sorry, just apologizing in case you did already have this trick going and i just overlooked it.
All the best.