This user has no status.
Member
But that's the thing - it's just a whip. If you crack a whip, this is the pattern you make. I have a better idea why you are calling it double but you don't crack a whip on the backswing.
NL, this is a fine bit of explanation. Cracking the whip is much more pronounced than mere whip mechanics, and I know that I, for one, will find greater clarity in visualizing the effect in serving if I remember to think about "cracking" the whip.