I havent done physics for a long time so i wont go into purely theoretical concepts, but I'll provide similar examples in totally different activities. Ever opened a bottle of wine with a corkscrew? the twist motion helps the corkscrew go further in the cork. Ever played pool (billiard)? Many professional players perform breaks at the begining twisting the queue at the end of their motion when they are about to touch the cue ball. It gives you extra strength. Again, those are just examples that illustrate the principle at the origin of the hip motion for a front kick. Ask him to try it by himself, a kick with and without the motion.
when it becomes a lecture im thinking "i wonder what sensei would do if i just kick him", "wow that girl is hot, ima spar with her", "i would have been a black belt by now without all this talking"...and on and on...
Shorei Shobu Kan Goju Ryu: white (1,2,3 green stripes) green (1,2,3 brown stripes) brown (1,2,3 black stripes) black (1-4th degree) akashiro (5-8th degree) (white/red) red (9-10th degree)
trainning for glory and trophies is never a bad idea. i train for personal growth, mentally, physically, you could try that. As for the girl, though one, ive been in that situation. If its strong it will survive, if its not then you'll remain friends.
it is called static streching i believe. you probably not like my answer, but to be good at it, just do it more often (mornings and evenings) and the best you can. with perseverance you will improve. And also dont limit yourself to static streching. Do active and passive as well (google it).
ShoreiShobuKan Goju Ryu: Hookiyu Kata (dai ich, ni) Gekisai Kata (dai ich, ni, san) Gekiha Kata (dai ich, ni) Saifa Kata Seyiunchin Kata Gakuse No Kata Seisan Kata Sanchin Kata (long, short) thats 13 Katas. for 11 of them you also learn their bunkai.