Originally Posted by rkelley
If you want the big topspin, the racquet has to have a large upward component to its velocity that is perpendicular to the ball. That's just physics - like you said swing up.
That's not physics actually. What you depict here is a major misunderstanding.
Spin is the edge of the ball moving relative to its center. Let's simplify the problem for you to grasp it. Let's say the ball is only two-dimensional (it's a circle). If you apply a vector is directly forward-directed to the upper edge, what happens? The edge moves forward, which is the same as saying that the edge which is bellow moves backward, which is the same as saying that the front edge moves downward and that the back edge moves upward. In essence, in front, bellow, behind or over... it doesn't matter, all of them can produce spin. That's physics. You do not need to have a vertical force to generate top spin because top spin is not directed upward.
Our real possibilities are hitting the upper edge or bushing the back of the ball.
Unless you swing at more 45 degrees from an horizontal plane prior contact, most of your swing is directed forward... With a greater amount of force directed forward, it seems logical to assume that accelerating the upper edge is a better strategy.