Can someone explain this martial arts move with physics

[mr friendly guy]

How the hell does he manage to hold off two guys like that? The explanations I can think of are

1. The two guys weren't really pushing hard and they only fell forward when the Sifu let go because they are in a unbalanced position (ie their centre of mass is quite forward).

2. The guys pushing are not just pushing in a left to right direction, but portions of their force is directed upwards. Thus weakening the force used to push the Sifu back.

3. The Sifu is standing in such a way, which shifts his centre of gravity slightly (presumably lower) - a similar way to the trick where a small lady can stand in a way such that even a strong man can't lift them up (like in that Penn and Teller series ).

Any ideas?

[LaCroix]

This is a classic trick of wing chun. We learned to do this in class. (This guy is actually doing a sloppy version of it, and I even have seen some street magicians do it, as well.)

The Sifu is creating tension with his adductors, and "sucking" himself to the ground (akin to a skater or surfer), onto an imaginary third leg that is where his (inward rotated) knees would touch the ground.

Due to various muscle and skeletal mechanics, this pose allows someone with resonably well-trained lower back and abs to re-route the force of his offender into a downward pressure.
When you do it, it's surprisingly easy, apart from the need to absorb the "weight" of the pressure applied with your hip and leg musculature. It really feels like the guy was pushing down on you, and your legs acting as a spring.

Also, you are not countering his force, at all. If the guys would suddenly vanish, the "unmoveable" Sifu would not fall forward, but would simply stand up taller, like a spring that is no longer compressed.

[cosmicalstorm]

I have seen more than one video of "masters" who decide to show their skills against others than their own students and suddenly it dosen't work.

[LaCroix]

This works, my master was willing to prove it with everyone who wanted to. This is considered kind of a party trick, like blowing out candles with a punch.
It is in fact a variation of unmoveable man, but you do it without your hands, using your rump musculature. Hell, even I could do it to a degree. You just need to train it for a while to develop the muscle control and necessary to do it.

edit: mind the fact that it won't work if you push directly on his shoulders. The fact that the other pushes against his arms is the essential thing.

[Scrib]

Also,am I the only one that thinks that the second guy is pushing downwards-or just holding him- on the first guy instead of forward or on the Sifu? Either way his full power does not seem to be in it.

[Stark]

I've seen an 80 year old man stand similarly while a huge footballer tries to push him over and can't. It certainly doesn't require some kind of student prep, and it seems that it's impressive solely because they don't behave the way you expect a body to behave when you push on them. It's not magic.

[Terralthra]

Also, most of the force of the second guy pushing does not get transmitted to the sifu in question. If they both pushed him, it wouldn't work.

[Stark]

If they pushed him differently it probably wouldn't work either.

[Dominarch's Hope]

Of course, once you have a hold of them like that, you could just pull them down.

[LaCroix]

If they pushed him differently it probably wouldn't work either.

Yes.
The trick is that you make them push you mostly down into the ground. That's why he held his arms out and in a slight angle - the moment you lock your elbows or your hands touch your chest, they send you flying.

It's hard to explain the mechanics, but you make them push at you in an inefficient angle, and the power that they do transmit gets eaten up in your arms, shoulders, and using your back (and superior balance) as a 'pivot point', you deflect the rest of the power into your legs, bending your knees.

As I said, it's a party trick that needs a bit of real training to make it work, like that "bend spear at the throat" and the "break cinderblocks with a sedgehammer on his chest" stuff, only these two demonstrate strenght, while this is a test of your balance and flexibility.

[Grumman]

2. The guys pushing are not just pushing in a left to right direction, but portions of their force is directed upwards. Thus weakening the force used to push the Sifu back.

While this trick has been pretty well explained, pushing upward would actually make it easier to move the guy. In the extreme case you'd lift him off the ground entirely, rendering his stance a non-issue.

[Zixinus]

I have seen more than one video of "masters" who decide to show their skills against others than their own students and suddenly it dosen't work.

True, but you can tell that it isn't by the fact that he is just showing it for what it is: a trick, to demonstrate the stability of his stance. It doesn't say that this stance will save you or will guarantee you victory or any other nonsense those guys usually say.

[Cykeisme]

I'm going to assume there's is a proper physical explanation, but can someone actually provide it?

How's that unmovable man thing work, as well? With the unmovable man thing, what if you simply took a step forward while pushing on the other person's shoulders?

[LaCroix]

I'm going to assume there's is a proper physical explanation, but can someone actually provide it?

How's that unmovable man thing work, as well? With the unmovable man thing, what if you simply took a step forward while pushing on the other person's shoulders?

*sigh* you didn't read my posts, right?

And again - if you push at the shoulders, the trick doesn't work.

[Terralthra]

The sifu's arms are dampers, like shocks on a car, and all he has to do is hold the first guy, since the second guy is not really pushing on the sifu at all.