Thanks for all the replies. I did some digging on the Internet last night and found a great article about this topic. I highly recommend that you guys download it and read every single word in it. The article is by Professor Brody and is titled “Unforced errors and error reduction in tennis” http://www.ncbi.nlm.nih.gov/pmc/arti...82/pdf/397.pdf
. I copied the relevant portion below.
However, an opponent will quickly catch on if every shot is returned to where it came from. A player who knows the facts about ball/racket interaction can reduce the errors that may occur even when changing the ball angle. If the ball is not going to be hit hard, it should be aimed a little closer to the centre of the court. With a hard swing, the shot can be aimed closer to the sideline or the corner with confidence.
The famous statement that the angle of reflection equals the angle of incidence holds for light reflecting from a plane mirror, but not for tennis balls rebounding from a racket.
Often, in a match, players ease up when well ahead and do not hit shots quite so hard. This can reduce the errors of depth, but can also lead to a problem. If the ball is still aimed the same way, but the swing is no longer as hard, balls that previously went down the line may now end in the alley.
A similar problem can result from changing the game plan in the middle of a match. A player may become concerned about the final outcome, so instead of hitting out and playing his or her regular game, may decide to play it safer and ease up on the strokes. Again, balls that previously went down the line may now end in the alley. The player ends up making more, not fewer errors. People will claim that the player “choked”, but what actually happened is that they did not understand the laws of physics (fig 1).
As the caption says, it describes the angle at which the ball comes off the racket when hitting a relatively hard hit ball at 20 degrees off racket hitting surface axis. 60 ft/sec is about 41 mph which means the opponent hit the ball initially at 91 mph (this is based on an assumption that the ball slows down to 45% of initial speed-check advancedtennis.com if you are curious).
What this tells me is that even if you are hitting a relatively hard DTL shot (at greater than 30 ft/sec=20 mph), the racket face should still point 5-10 degrees inward from the sideline whether you do this consciously or not. Otherwise, the ball will land in the alley.