Ian Dodkins wrote:
I wrote backward, because if it is irimi and it is done fast and with correct timing there is no time for uke to turn himself. However, if it is pretty static (or if uke is spinning more on their axis e.g. due to a redirection or a tenkan movement) a forward roll is more likely. e.g. if irimi-nage is being executed, but uke pushes forward towards nage (like a shoulder barge), and nage turns tenkan to allow a tenchi-nage to occur.
Actually, if the technique is done fast and correct you would flip over instead of taking a back drop (Koho Ukemi). The reason is your balance is broken so that your center of gravity cannot fall fast enough. Tenchi Nage attacks the body above the center of gravity, but not down. Your center of gravity cannot accelerate towards the tatami at move than 9.82 m/s/s with your feet staying on the mat, but Sh'te/Tori/Nage can cause the upper body to accelerate more. Hence Uke turns over!
Physics is great! Actually all Aikido is Physics. Long live Physics and realise Ki does not exist!