Article Written by: MARIAM MISSAGHI
A famous dance critic once said of the magic of dancing en pointe (in toe shoes), "It's that vision of freedom you create when you're defying physical law." But to truly understand how this magic vision is created, we must study the physical principles behind poite dancing. Having an understanding of these principles will improve dancers' technique, as well as deepen spectators' appreciation for the art of ballet.
History of Pointe Dancing
The first pointe dancing was donethe early 1800s. It became an accepted, widely taught technique in the 1830s after Marie Taglioni's performance of La Sylphide en pointe in 1832.
The three main parts of a toe shoe are the toe box (A), the shank (B), and the ribbons (C). The toe box, which is not made of wood as is commonly believed, but layers of canvas and linen held together with a special glue, supports the sides of the foot and provides a base for the toes to stand on.The shank is made of hard leather and supports the arch. The harder the shank, the harder the shoes are to break in, but the longer they last. When buying toe shoes, a dancer can usually choose a soft, medium, or hard shank depending on her skill level, the strength of her feet and her personal preference.The ribbons are sewn into the inside of the shoe to the liking of the dancer. They keep the shoe on and support the ankle a little bit.
There are all different types of toe shoes. Dancers select their shoes based on the shape of their feet, and what feels most comfortable.
What stabilizes a dancer en pointe is the upward tension in the achilles tendon as the toe pushes down into the floor. The achilles tendon must withstand a tension force two to three times a person's body weight! The achilles tendon is vital to a dancer, and if it tears it can mean the end of a dancer's career.
How is it possible for a dancer to balance her entire body weight on one square inch (the approximate are of the pointe of a toe shoe). The key is that her center of gravity, that is the location where the mass of her body is concentrated, must be exactly in line with the area of support, that is the pointe of the shoe.
The state of static balance, that is balance without moving, can only be achieved when the sum of the forces on the body is zero. When a dancer is en pointe and is not holding onto anything, the only forces acting on her are the downward force of gravity, and the equal and opposite upward force of the floor that balances it. When a dancer relevees, she will be balanced if she relevees straight up, exerting zero horizontal force. However, she will be unblanced if she is slightly tipped one way or the other and exerts a horizontal force as she relevees, and she may topple. In order to relevee straight up a dancer must have enough strength in her legs, feet, and ankles, and she must maintain good form by not sitting in her hip or arching her back.
One of the most beautiful moves in ballet is the pirouette, a turn on one foot often with multiple rotations. The Law of Rotational Inertia, a variation of Newton's First Law, states that an object that is not rotating will not begin rotating, and an object that is rotating will not stop rotating unless acted upon by an external force. Rotational inertia depends on the distribution of the mass of the object relative to the axis of rotation. The greater the distance between the bulk of the mass of an object and the axis of rotation, the more rotational inertia it has. This explains why
when a dancer pulls in her arms while she is spinning she has less rotational inertia, and therefore spins faster and for longer. This also explains why the rate of turn of a pirouette in the retire position (the most common position for a pirouette with the gesture leg bent so that the toe is placed at the inside of the knee of the supporting leg) is more than double the rate turn of an arabesque turn (when the gesture leg is extended out behind the dancer).
Starting a Pirouette:
In order to begin a turn a dancer must exert a force that will overcome her rotational inertia. This force is called a torque. and it is defined as the turning force that creates a rotational acceleration; in other words a torque is applied to make an object spin. The strength of a torque is determined by the amount of force put into it, and the lever arm .(Torque = force multiplied by lever arm). The lever arm is the perpendicular distance between the pivot point and the point where the force is being applied. This explains why a pirouette from fourth position, a position where one foot is about a foot in front of the other, has more momentum than a pirouette from fifth position, where one foot is directly in front of the other and they are touching. A pirouette from fourth position uses a greater the lever arm, and therefore the torque is increased, and therefore the turn has a greater angular/rotational momentum. or strength of rotation (Angular momentum = rotational inertia multiplied by rotational velocity). Angular momentum comes from the arms, the torso, and the leg lifting. So to begin a turn, a dancer exerts a torque by pushing down into the floor with her feet. When she does this, she exerts a horizontal force on the floor, which in reaction exerts an equal and opposite horizontal force against her which she uses to "push off" and begin to turn. The key to this is that a horizontal force, which is an external force because the only other forces at work are vertical, and this changes the body's rotational inertia and allow the body to spin.
Once a dancer is spinning, as long as she keeps a straight form with her body mass as close to the rotational axis as possible and a lifted center of gravity, she will continue to spin until friction slows her down and eventually stops her. However, because the area of contact between the shoe and the floor is so small, there is not very much friction.
Stopping a Pirouette:
As soon as a dancer places her feet down, she has exerted a torque of mostly fricional force which changes her rotational inertia and stops her from spinning.
What the Arms Do:
The motion of the arms plays a large role in starting, spinning, and stopping the pirouette. When starting the pirouette, a dancer extends the arm opposite the direction she is going to turn out to her side (i.e. If she is doing a left pirouette she extends the right arm). In this position a dancer has more rotational inertia which extends the time that the torque is exerted. As a dancer begins her turn, she pulls in the extended arm close to her body and her rotational axis to meet the other arm. This motion helps to whip her around, and changes her rotational inertia so that once she is spinning she can spin for longer. When stopping the pirouette, a dancer extends one or both of her arms to change her rotational inertia again so that she decreases her rotational velocity and slows down, and to give her balance as she places her feet down and comes to a stop.
Where I Got My Information:
The Dance Shop :[http://www.22dance.com/pointe]
ABC Dance :[http://www.abcdance.com/pointe]