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 Post subject: Posted: Sun Sep 25, 2005 1:55 pm
2Green wrote:
It's just a physics point, I'm not saying speed is unimportant in hitting or anything like that.
NM

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 Post subject: Posted: Sun Sep 25, 2005 1:56 pm
jorvik wrote:
maybe ask your Sensei to post one, all this physics stuff is bloody Chinese to me

Show me the MONEY!!!! (money shot that is)

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 Post subject: Posted: Sun Sep 25, 2005 6:03 pm

Joined: Thu Sep 23, 1999 1:01 am
Posts: 1509
Location: on the path.
(Bronze)
"E.G. What is the probability that you can actually hit something with 99% of X power you can generate while it's moving at random speed and direction?"

I'd agree with your answer: probably zero! Especially if it's moving FAST and random!

NM

_________________
The music spoke to me. I felt compelled to answer.

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 Post subject: Posted: Sun Sep 25, 2005 6:08 pm
Ok, but post the video of that kick! I wanna see this thing!!!!

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 Post subject: Posted: Sun Sep 25, 2005 8:11 pm

Joined: Wed May 15, 2002 1:01 am
Posts: 1444
This thread perked my interest at the first post by Neil with this statement
Quote:
In this kick the ONLY velocity required is the amount to get the foot onto the target. THEN the damage occurs in the "explosion"

Neil, then you stated
Quote:
if one is going to use a formula to prove a concept, you may as well use the right one, that's all!

What formula applies to this transfer of energy?
No matter...we are only one hour away from each other, I`m willing to test the kick. Then I will understand the body mechanics used. I have learned much from volunteering as "Demo boy" over the last 28 years, Clayton... (remember Popeye as Van called him) he always proved his point in few words and man those toes of his
This kick if it works for me would be good payback for when I see him in late October.

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Léo

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 Post subject: Posted: Sun Sep 25, 2005 10:13 pm

Joined: Thu Sep 23, 1999 1:01 am
Posts: 1509
Location: on the path.
Good point.

This thread started as a question from me about a type of kick I was introduced to by some guys I train with who came back from the summer camp and showed it to me.
I thought you all knew about this from long ago and I wanted more info/opinions on it from more experienced UechiKa so I could maybe train it better..

Then the thread took on a SECOND emphasis when someone said that F=ma can prove the delivered force in a blow, whether kick or hand strike.

I said no, that's the wrong formula to show that.
**************************************
The two aren't connected.
I never said, and am not saying now that I have any formula to "back up " my concept of the low-velocity kick -- I'm still trying to get info ABOUT it.

The formula thing is a red herring, and unrelated. It is just a statement about the confusion caused when people try to "illustrate points" in training by invoking physics, and unfortunately use an inappropriate example.
This is caused NOT by lack of math, but by lack of concept -- that was my point.

I don't think we should invoke physics, or any other higher concepts to explain martial arts. It will only get us in trouble, and waters deeper than we were prepared to swim in.
We should just be exposed to real examples, as I was, and ask questions about how to do it ourselves.

NM

_________________
The music spoke to me. I felt compelled to answer.

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 Post subject: Posted: Sun Sep 25, 2005 11:50 pm
“That’s not Uechi!”

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 Post subject: Posted: Sun Sep 25, 2005 11:55 pm
Look forward to hearing Leo`s take

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 Post subject: Posted: Mon Sep 26, 2005 12:15 am

Practically unless trapped in close it is not one I would use but it is done.

I often use it to show how connected mass affects the impact.

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 Post subject: Re: Nonzero 'Jerk' is key in the striking situationPosted: Mon Sep 26, 2005 6:25 am

Joined: Mon Dec 15, 2003 12:29 pm
Posts: 203
Oldfist wrote:
Let m(t) be the mass as a function of time t and let v(t) be the velocity as a function of time t, then the momentum as a
function of time t is p(t) = m(t)*v(t). Further let ' represent one derivative with respect to time, i.e. the instantaneous time
rate of chang of a quantity, then

F1 + F2 + ... + Fn = p'(t) = [m(t)*v(t)] ' = m'(t)*v(t) + v'(t)*m(t) [by the product rule for derivatives]

This form of Newton's 2nd Law is needed to compute the force, for example, on a rocket whose total mass is changing
because it is burning its onboard fuel. So, to describe the force on a constant mass m (or the acceleration produced by a
force on the constant mass m) the simplified version is:

F = m*v'(t) = m*a(t), where the acceleration (the instantanteous time rate of change of the velocity) is a(t) = v'(t).

If we take the (over simplified) example of the 1-dim motion of an object in the gravitational field of the earth (e.g. hold
your pencil up over the floor and then release it) then the acceleration is also constant, i.e. a(t) = -9.8 m/s^2.

However, the acceleration can also increase and a familiar example is driving your car.

Case 1. a(t) = 0
Suppose you are driving your car down the street at a constant rate v(t) = 30 mi/hr, and so your acceleration a(t) = 0.

Case 2. a(t) = c (constant number) != 0
Now, suppose you enter a zone in which the speed limit is 40 mi/hr, and you uniformly press down on the accelerator
producing a constant, nonzero acceleration which gradually and uniformly increases you velocity to 40 mi/hr.

Case 3. a(t) = nonconstant function of time
Now, a key thing to notice for our striking application is that the acceleration may be itself increasing and this occurs when
"punch it" into passing gear, that is, instead of uniformly pressing down on the accelerator, you floor it. In this situation you
experience what is called the "jerk" and that is a nonzero time rate of change of the acceleration itself.

Summarizing, if s(t) is the position as a function of time t, then

v(t) = s'(t), the velocity function, i.e. the instantanteous time rate of change of the position
a(t) = v'(t), the acceleration function, i.e. the instantanteous time rate of change of the velocity
j(t) = a'(t), the jerk function, i.e. the instantanteous time rate of change of the acceleration

F = m*a(t), if we look at this simplified case of Newton's 2nd Law in which the jerk is nonzero and positive, then that
means that the time rate of change of the acceleration is positive, and hence in this case the acceleration is increasing,
which means that the force is increasing, when the jerk is nonzero and positive. This is the interesting case that applies to
the striking situation.

Energy analysis is of course good stuff, but it's not the only approach. One can start with the above, F = m*a(t) = m*(dv/dt) and approximate it for small delta t , yielding the impulse-momentum theorem:

F*(delta t) = delta (m*v) = m*(delta v), which says the impulse is equal to the change in momentum. So, we can use consevation of momentum instead of conservation of energy to compute F in newtons or pounds. Similar to:

http://www.fas.harvard.edu/%7Escdiroff/ ... eBlow.html

Either approach allows us to compute a quantity at impact, however, neither by itself explains why one method of striking is "harder" or more effective than another. An analysis of the jerk which occurs before impact, partially describes a key feature of the why. In order to do an experimental analysis we would need a very sophisticated, high speed motion capture camera. This type of analysis is standard stuff for sports scientists, but is nontrivial even for the experts. Just because one may have only a high school or non calculus-based understanding of physics and can't see how to do it doesn't mean that it can't be done.

Tony, BTW, this is classical mechanics which we can apply using simplifying assumptions and that the strike has been made. The probabilistic situation you are interested in, in which evasion occurs, and which isn't really random, would require a statistical mechanics type approach, and yes the math would be different.

_________________
John

I am always doing that which I cannot do, in order that
I may learn how to do it. Pablo Picasso

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 Post subject: Posted: Mon Sep 26, 2005 7:56 am
Oh, so I my instincts where correct then...

How about we just post the video of the kick?

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 Post subject: Posted: Mon Sep 26, 2005 10:27 am

Joined: Sat May 14, 2005 7:22 am
Posts: 73
Location: Quebec
I have only really skimmed through this thread, and have not read any of the physics stuff, so this might be totally unrelated, but I would like to relate something that happened to me this weekend that seems like it has some bearing on this.

I was working out with a Tai Chi/Shotokan guy (I know - seems like a strange combination but man this guy is good). Anyhow, he was teaching me a version of push hands (a pretty "violent" version). At one point, we were isolating the "push" part of it. He had his hand on my chest to demonstrate, and he just kind of "dropped" into it and pushed out at the same time. All of a sudden I HEARD all the air hiss out of my lungs and found myself 4-5 feet from where I had been.

I wouldn't say that what he did felt like a push or a shove, it felt more like an explosion. I would imagine that if he did the same thing with some momentum (as in a strike) that the effect would have been quite unpleasant (for me ). Anyhow, I wonder if this LV kick isn't kind of like this guys "push". Using great body mechanics, he created an explosive impact with no wind up. But with the extra momentum it would be much more devastating.

Anyhow, if this has nothing to do with the LV-kick...

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 Post subject: very good observationPosted: Mon Sep 26, 2005 12:52 pm

Joined: Wed May 15, 2002 1:01 am
Posts: 1444
Asteer wrote:
I have only really skimmed through this thread, and have not read any of the physics stuff, so this might be totally unrelated, but I would like to relate something that happened to me this weekend that seems like it has some bearing on this.

I was working out with a Tai Chi/Shotokan guy (I know - seems like a strange combination but man this guy is good). Anyhow, he was teaching me a version of push hands (a pretty "violent" version). At one point, we were isolating the "push" part of it. He had his hand on my chest to demonstrate, and he just kind of "dropped" into it and pushed out at the same time. All of a sudden I HEARD all the air hiss out of my lungs and found myself 4-5 feet from where I had been.

I wouldn't say that what he did felt like a push or a shove, it felt more like an explosion. I would imagine that if he did the same thing with some momentum (as in a strike) that the effect would have been quite unpleasant (for me ). Anyhow, I wonder if this LV kick isn't kind of like this guys "push". Using great body mechanics, he created an explosive impact with no wind up. But with the extra momentum it would be much more devastating.

Anyhow, if this has nothing to do with the LV-kick...

I think your right on (can`t be sure as haven`t experienced 'LV" kick)
Compression is a great deal of what I think you felt, we actually have it in Uechi. The "wrist block" sequence in the Hojo Undo (Konchin) demonstrates this very effectively. If Richard "Spike" reads this please feel free to chime in as we often work this type of "push" together in class.
Rick Wilson: Do you agree that this may also relate to "QWA"?
http://forums.uechi-ryu.com/viewtopic.p ... qwa#111871

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Léo

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 Post subject: Posted: Mon Sep 26, 2005 2:10 pm

Joined: Sat Oct 26, 2002 1:01 am
Posts: 205
Location: South Shore, Nova Scotia, Canada
Leo,

Will post later, no time right now. Off to work I go

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Richard
http://www.nskarate.tk

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 Post subject: Posted: Mon Sep 26, 2005 2:51 pm
I'll give you an example of a low velocity kick
I went to this Uechio dojo and I was sparring with this bodybuilder type when suddenly he let loose with a straight kick to my stomache, kicked me across the room
now I'll be honest the guy looked impressive .and I really didn't want to fight him................but I dunno, he hit me and I've gotta hit him back, so I didn't want to hit him too hard ( In case I made him mad ).........but I had to hit him. so I did a thai style leg kick but I was too close to really gain momentum so I just kinda lifted my leg, sort of a cross between a kick and a knee strike ......anyway the fella went kinda white ( actually the colour of boiled schitte )..I thought that I'd embarressed him, coz I was a white belt.but years later I was shown this technique as a Thai boxing kick.....I was told to do it slow coz it was a real killer ....but I really whacked it in on the bodybuilder

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