Originally Posted by toly
It is absolutely obvious that in order to hit through 5 bolls the racquet should move along a straight line at least 10’’ with stable racquet face orientation. “Piston stroke” can provide this, but you don’t want to utilize it because it is slow motion. Then, you should think about approximation of the strait line.
Osculating circle of the straight line is infinity. Thus, if you use rotational motion only, you have to increase radius of rotation as much as possible. From this point of view, straight arm FH is probably the best, because that creates maximum radius. However, most pros use bend elbow FH. So, they don’t care about hitting through.
If you know some different but particular way to “control the curvature to some extent, so as to meet the trajectory smoothly”, just let me know please.
The particular way is the intuition of the pros. Just like it is meaningless to ask how Nadal produces a curved trajectory of the ball thinking that he uses mathematics for it.
As far as hitting 5 balls in a row, OK that may not be 5, it may be say 3.
Here is a simple calculation. TW University uses a racket tip speed at impact of 80 mph for ATP forehands. You can do a calculation of how much the tip will travel in a 4 ms dwell time, and it comes out to be 5.7 inches, or 2.2 ball diameters. Add in the fact that for a little more time the racquet will be maintaining its inertia after the ball leaves, and 3 balls in a row is not unimaginable.
Does it mean that the pro guides his racket in a straight line towards the target? No. It just means that he makes solid contact towards the intended direction as part of his up, forward and leftward trajectory of the swing.
I have said many times that topspin cannot be produced by purely rigid bodies. There has to be deformation in a certain dwell time. If you meet the ball in a certain way, it will be deformed and released in such a way that it will have both forward momentum and spin. If you don't meet it solidly, it won't have much pace but will have spin from a grazing motion. The solid meeting is what is commonly called hitting through the ball, and also produces the "pro sound" on impact. The reason it is emphasized is that club players often hit tentatively.