Pirouettés
Pirouettés,
French for "to whirl about," are some of the most common steps
performed by both male and female ballet dancers. Pirouettés
come in all different shapes and sizes. They can be in retiré,
coupé, a la secondé; with arms in first or fifth; one half
turn to six, seven, or eight full turns!
If
you were to walk into a ballet class you would hear many
"physics" terms mentioned, specifically when discussing
turning. The two most common terms heard when practicing
and trying to improve pirouettés are force and momentum.
The words seem to be tossed around, but they actually have
a very strong application. When turning in any position
you have to be mindful of a of two very important things:
performing full rotations and staying balanced. Every turn
starts from a preparation, a position that a dancer pushes
off from the floor. After applying an initial force from a
plié (bent legs) the dancer's legs and arms move quickly
to the turning position.
As shown in the
video above, the dancer has a supporting leg (and foot)
that she turns on and a working leg that moves to the
turning position. The supporting leg is tasked with
initiating the turn by exerting a torque on the floor.
Torque (force*distance) changes depending on the
preparation position and how much the dancer bends into
the plié. Turns are frequently done from fifth or fourth
position. Since the distance between the working and
supporting leg is larger in fourth position than fifth, a
dancer can exert a larger torque from the same amount of
force, generally making it easier to complete full
rotations. The position of the dancer's arms also changes
how a dancer turns. Pirouettés usually have arms in first
or fifth position, and depending of the placement of them
the dancer has to adjust since their center of balance
changes.
Another factor to
consider when performing turns is the position that the
dancer rotates in. A dancer's inertia is larger when legs
and arms are extended compared to when they are close to
the body (e.i. the axle around which the turn takes
place). In order to turn faster a dancer can decrease
their inertia by bringing their arms (or leg) in slowly as
the turn progresses. The dancer will eventually come to a
stop no matter how big a torque is exerted because energy
is being lost between the floor and ballet shoe; however,
a dancer can increase their time turning by bringing
extremities in, keeping their axis of rotation (working
leg through the top of the head) stable and perpendicular
to the floor, and leaving from a larger starting position.
Men, due to the shape of their shoulders and hips, turn
very easily and quickly. This allows them to complete
several turns moving from larger positions into smaller
ones.
As you can see in the video above,
the dancer's angular velocity increases as his moment of
inertia decreases. This allows him to keep turning as the
friction between the floor and his shoes slows him down.
All images courtesy of Pittsburgh Ballet Theatre
