Re: Down to the Ball
The idea of swinging "up" is to keep the path of the bat as close to the path of the incoming pitch, which is angling down. The angle of your swing/rotation will be based on the position of the pitch in the strike zone. The lower the pitch, the more tilted your bat path will be. The higher the pitch the more flat it will be. By matching your bat path to the ptich path, you increase your odds of solid contact.
Coincidentally, I happen to be a computer scientist, mathematician and physicist. The physics I have seen discussed and presented by Jack on this site and in his videos is solid.
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