From: USERHEJF@UMICHUM.BITNET (Eric B. Arnold)
Newsgroups: rec.folk-dancing
Subject: Subject: "weight" in allemande bwas:NECD(New England Contra Dance)U
Date: 8 Apr 92 01:49:30 GMT

On 1 Apr 92, prs@strobe.ATC.Olivetti.Com (Phil Stephens) writes:
 
> Being given more "weight" than my muscles and tendons can handle sometimes
> is (but that's another subject.  Still, why isn't 5-10 lbs enough?  Why go
> for 20-30?  Except with those few who also want to do that, of course!)
 
A little elementary physics may shed some light on this subject. One of the
pleasures of contradance, for me at least, is the appropriate use of force
applied through tension in the arms to help dancers change direction with
a minimum of effort. Frequently, as in allemandes and circles, all of the
dancers need to change direction at the same time, and the forces that help
one also help the other(s) in like fashion. If there is no one to hang on
to, walking in a circle of the size that one traverses in a typical allemande
at the typical speed that one moves in a dance (about 3.5 mi/hr, a fairly
brisk walk) is distinctly difficult, because all of the force required to
change the direction of your momentum must come from your feet, and that
force must be sideways if you are facing in your direction of travel around
the circle. If you have a pole to grab onto while you go around it becomes
much easier, because the direction of the force applied is in exactly the
right direction to change your motion in the desired way without having to
use your feet to apply this sideways force. Similarly, two people of equal
weight (mass) grasping hands may achieve the same effect because the forces
are the same on each side due to the symmetry of the distribution of weight.
 
We may estimate the force required to achieve this mutual change in direction.
Let us assume that the dance tempo is 108 beats/minute, that a circle of four
is a rotating square 5 feet on a side and gets around one complete circle
in 8 beats (steps), and that dancers doing an allemand travel at the same
speed in the allemande as they do in the circle. The velocity of each dancer
in the square is very close to 5 ft/sec under these circumstances, which is
a bit over 3.4 mi/hr, a reasonable speed. If the dancers are 4 ft apart in
the allemande, slightly closer than the 5 ft in the circle, then the
centripetal (toward the center) acceleration required for this motion is
12.5 ft/sec/sec, or about .39 g (acceleration of gravity). The force required
for this acceleration is the acceleration in g's times the person's body
weight, so for a 150 lb person would be 58 lb force. At this level, there is
no need for a sideways force by the feet. Perhaps this explains why many
people like at least 20-30 lbs force through the arms -- that does make things
significantly easier, while 5-10 lbs is barely noticeable.
 
When dancers' weights are not the same, an imbalance results which must be
compensated for by a shift in the center of rotation (closer to the heavier
person) and/or more compensatory force through the feet, with correspondingly
greater difficulty.  The force increases with the square of the velocity and
is inversly proportional to the first power of the radius of the circle that
a person traverses, so increasing the distance between dancers decreases the
force.
 
I feel that, because a large force is definitely useful in what I consider to
be good dancing, that an allemande grip that has thumbs between thumb & fingers
but not tightly grasped is most useful -- it helps prevent the hands from
accidentally coming uncoupled but enables disengagement promptly when dancers
are ready to proceed to the next figure.
Xref: sparky rec.folk-dancing:1064 rec.music.folk:3136