[Tango-L] Axis vs. Balance

[Jay Rabe]

     Apologies to those who just want to dance, but some of us find benefit 
in highly technical analysis...

     :-)

     Michael and Evan have both clarified the respective definitions of axis 
and balance. Being "balanced" means that your center of mass is vertically 
inside your footprint, and you can be motionless without falling. Axis 
really only has meaning in the context of rotation. Strictly speaking, 
Michael's hanging belt defines the center of mass, though I too use the term 
axis to refer to it. Perhaps Even can confirm, but my suspician is that the 
axis of rotation of a dancer is always a line that passes through the center 
of mass.

     OK so far. But I want to present a separate, though related concept. I 
call it the "precision of the axis." I believe it relates to the 
mathematical property of "moment." If a follower is standing motionless on 
one leg, then two things are true. She is balanced, and her center of mass 
is within the footprint of her standing foot. These things are true 
regardless of what her free foot is doing (assuming at the start, for 
simplicity, that it too is motionless.)
     Now consider two cases: First, in which her free foot is collected 
close beside her standing leg. Second, she is holding her free foot/leg out 
away from her body. In both cases she is still balanced, and her center of 
mass (axis) is vertically above her standing foot. But her rotational 
properties are very different. With her free foot collected, she can pivot 
and turn very quickly. With her free foot extended, it takes more effort to 
generate the momentum needed to make a quick turn.
     Another, more subtle effect, is that, with her free foot collected, she 
cannot sustain much movement off her axis before she will be out of balance. 
If at the start her axis is precisely over the center of her foot, then the 
most she can move sideways is 1/2 the width of her foot, and the most she 
can move front-to-back is 1/2 the length of her foot, before she will be out 
of balance.
     If OTOH her free foot is extended, and her torso (most of her mass) is 
moved, she can compensate by slightly moving her free foot, and its 
associated mass, effectively moving her center of mass, and thereby 
maintaining her balance, keeping her center of mass within her footprint.

     As a leader, the dynamics of doing a single-axis turn are quite 
different depending on whether the follower's free leg is collected or 
whether it is extended, as I mentioned above. But the most challenging 
situation occurs when the follower changes the position of her free leg 
(changes the position of her center of mass and her resulting axis of 
rotation) DURING the turn. A leader must be sensitive to where her axis is.
     In practice, it sometimes happens that the axis of such a turn wobbles 
like a slowly-spinning top during the turn. Ideally both dancers should be 
balanced at the End of the turn, so that they could pause without having to 
"fall out of the turn" by stepping to regain their balance.

     J
     www.TangoMoments.com


----Original Message Follows----
From: "Michael" <tangomaniac at cavtel.net>

I've read the "off axis" messages. I got the impression that some were using 
balance and axis synonymously. They're not. Here's an experiment. Take a 
belt with a heavy buckle. Put the end without the buckle in your sternum. 
(This is the indentation in your chest). Put your feet together.  Stand on 
your right foot.  The belt buckle will move over your right foot. Now shift 
all your weigh to the left foot. The belt buckle will move over your left 
foot. Your axis is over the foot you're standing.

Now stand with your feet apart. Shift as much weight as you can to your 
right foot. The belt buckle won't move completely over your right foot 
because some weight will be on the left foot because the feet are apart. In 
this case, your axis is somewhere between your feet because all your weight 
ISN'T on one foot.

You have balance AND axis in both cases. However, your axis isn't in the 
same place when your feet are apart compared to when they are together. This 
is why your feet have to be together before pivoting. If the axis isn't over 
one foot, your turn will not be completely circular (such as the man leading 
a molinete). If a woman's feet aren't together, as she pivots for an ocho, 
some of the momentum from the pivot will send her outside the circle.

Hope this helps.

Michael Ditkoff
Washington, DC
Hated geometry in high school. Maybe I'd be a better dancer if I understood 
it better  XX years ago.


I'd rather be dancing Argentine Tango
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