I've found a video that shows perfectly how Nadal's topspin forehand affects the curve, angle and bounce of the ball filmed in 720p HD from the back. Put it in 720p to watch it clearly.
It was filmed in a practice session in Indian Wells (hard court). It shows how the ball curves through the air (just imagine how a banana show must curve watching it in this spectacular perspective. The banana passing shot against Birdie in the Wimbly final was insane, now I realize how curved it had to be. Unbelievable) and then bounces and the spin produces new angles. He also can modify the height of the ball when it bounces.
Imagine this kind of shot in every single point, with a minimal rate of UEs, during 5-sets and knowking this monster is a mental giant always focused. Imagine this on a clay court if he can produce this effect on hard
I've posted it because it reflects really well how Nadal's game works. He does not moonball, he simply hits the ball with an unprecedented topspin. To hit back a ball from Nadal has to be like hitting a friggin rock, too much weight in the ball to handle.
Credit to the user that filmed and uploaded it.
PS. After peaking in 2008, Nadal uses is hard flat crosscourt BH to put pressure on his opponent, forcing him to hit a soft high ball to continue dictating the play with his FH.