For many ballet is a form of art, something to be perfected through years of training. For Ken Laws, ballet is a game of physics. Law is a physics professor at Dickinson College, and he also teaches ballet classes. When he believes students could be performing a step better he explains to them, in terms of physics, how to correct their movement.
Three steps are discussed at length in the article, a grand jete en tournant, and fouettes. The videos below show these movements:
Grand jete en tournant:
Laws explains that when performing a grand jete en tournant, one must use the torque of their body to turn through the air. He says the dancer's angular momentum is equal to the rate of spin multiplied by the moment of inertia (which depends on how the dancer's mass is distributed around her spin axis). The 180 degree turn can be turned into one and a half turns by bringing the legs together at the top of the turn, bringing the legs and arms into the axis of rotation, and holding them there. Conservation of angular motion allows the dancer to then complete the extra rotations.
The grand jete is a perfect parabola. Laws says that once the dancer leaves the floor there is no way to alter the path taken, however, by opening the legs when nearing the top and closing them while coming down from the jump, the dancer uses her legs to "take up most of her center of gravity's vertical motion."
Finally, in the fouette turn, the whipping leg stores momentum as the dancer turns and then returns it to the body by tucking it back in. It is also important to note that when the dancer rises in a balance their body must be perfectly perpendicular to the ground in order to sustain the position - this way their center of gravity will remain in tact.
Laws argues that conservation of motion is the most important physical principle in ballet as it can be applied to many jumps and turns. His application of the rules of physics to ballet allows him to not only give form corrections to dancers, but to explain how altering their movement according to the laws of physics can help them to correctly execute the step.