Raul Rodrigo wrote:
Angell is converting the horizontal force of the push into a vertical one, diverting it into the ground. (its vital that his hands are on uke's elbow, it helps him divert the force downward) Its a trick that Shingo Nakao Shihan showed to my sensei. Though we haven't done it with ten people pushing. I've seen an aikido shihan, Motohiro Fukakusa, do the unliftable body trick. I have no idea how he does it.
All of those things are standard Ki Society exercises and are not particularly difficult to do if you are relaxed and coordinated. I'd wager that most of the aikido teachers you may have seen doing such things picked it up from Tohei Sensei, he was after all the aikikai chief instructor so his influence would have travelled quite far. Of course there's no way to verify that other than asking the sensei concerned where he/she learned to do it.
With regard to the horizontal force, only the first two or three people really make a difference, all the rest are just pushing each other and not really contributing to the force placed upon him, adding extra people makes it look more impressive but thats all it does IMO.