Ki Power  Dropping the Tanden in Aikido IntroductionIn Aikido the student is encouraged to drop his / her body a various times throughout just about every technique. Why? Physics can provide part of the answer by doing a calculation of the power generated. The intention is for the dropped onepoint to transfer energy to an aikidoka’s training partner ( uke) in such a manner that they are projected or immobilized. Equally this power can be transferred to a sword for a powerful (but relaxed) sword cut. A look at how much power is generated by dropping the tanden just a few centimetres. The results show that this is phenomenal power available to everyone that just bend their knees. Do this at precisely the right time and with uke stretched out and it is dynamic yet effortless. Figure: Equivalent power you can generate just by dropping you knees a certain distance... its easy!!The geeky stuff (tune out now if you want)Key assumptions: Can accelerate the onepoint to gravity
(9.8m/S^{2})
 Entire body mass drops with onepoint (not
completely true since legs have a weight and are bending therefore not
dropping at 1g)
 Power generated can be effectively transferred
to uke.
Use Newton's laws of motion S = ut + ½ at2
 S
= distance traveled
 U = initial velocity
 T = elapsed
time
 A
= acceleration (use gravity)
 Work = mgh (work
done
in raising an object to height h, also released)
 M = mass
 G
= gravity
 H = height
 Power = W/t (Power generated is work done divided by the time it
took)
ResultsThe Figure below shows the power generated
as the onepoint drops for a 50kg (110lb) and 100kg mass. These would be
equivalent to a 50kg and 90kg person I guess. Note that after the onepoint has dropped only 10cm over 1hp is generated by a 50kg mass. This
then continues to increase – but not as rapidly over distance. Physics
shows how much power can be generated but using it effectively is
really the art of Aikido. If we have 3 horsepower at our disposal but
only move uke’s hand (because there is plenty of movement
available in
the elbow joint) it is wasted. Only if the slack in uke is completely
taken up can our 3 hp be effectively transferred resulting in projection
of immobilization of uke. ConclusionWell it sure is a lot of power that the one point is generating. But if its only being generated for a short period of time the trick really is to use it effectively. i.e. if nage hasn’t got a connection to uke’s one point then all this power will be wasted in taking up the slack in uke's arms or something like that. Enter ikkyo, nikyo etc.. these techniques allow nage to tighten up uke so that all (or most of) the power generated by the one point is transmitted directly to uke’s one point. Now if we are projecting uke then this power is effectively doubled by the ground because after being accelerated by the onepoint they are then decelerated by the ground. Appendix I – Matlab(C) code fragment from Figure 1 %calculate force, work and power over time of a dropping body
%matlab
code fragment
body = 50; % weight of body
gravity =
9.8;
watts_to_horse = 1/764;
s = [ 0:0.005:0.5]; t
= sqrt(2*s/gravity);
work = body*gravity*s; %use potential
energy = mgh
power = work./t; % power is work done over time
inst_power
= diff(work)./diff(t)*watts_to_horse; % look at work done in a
particular time step
plot(s(1:100),inst_power,s(1:100)+0.0025,inst_power*2);
% look at instaneous power
xlabel('Distance(m)');
ylabel('Horse
power (hp)');
title ('Power generated through dropping of one
point');
legend('50kg','100kg') 
