2Green wrote:It's just a physics point, I'm not saying speed is unimportant in hitting or anything like that.
NM
Your also not answering my question...
In this kick the ONLY velocity required is the amount to get the foot onto the target. THEN the damage occurs in the "explosion"
if one is going to use a formula to prove a concept, you may as well use the right one, that's all!
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.
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...
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