Originally Posted by Povl Carstensen
I find it rather revealing that some people have to make up that others propose that you hit the ball backwards, to have something to critisize and be right about. But it made me think about racket head acceleration. During the debate someone put forward (I can't find it now) that the foreward velocity decreases after impact, while the upwards increases. And ofcourse the sideways speed accelerates as the racket goes across the ball and/or body. And it is only natural that the foreward vektor goes down as the upwards and sideways goes up. If you factor them together, I think it is very likely that the combined sum goes up, meaning that the racket in a lot (most?) of typical modern forehands (and other shots as well) accelerate after and through impact. Maybe this is obvious to some, perhaps others disagree. I wonder if the movement in all three planes have been factored together?
In that study, sideways numbers were not supplied. I went back and calculated the resultant velocity of the forward and upward components at impact and it was 36 m/s. After impact, the first decreased and the other increased (up to a point) as noted by you above. I calculated the resultant velocity again when the upward component reached its maximum value, and it was 26 m/s. So, at least for the case when the sideways is ignored, there seems to be a net deceleration.