Conservation of angular momentumis perhaps the most important physical principle in ballet, but there’s more to ballet than rotation. Another classic move is the grand jeté, a gazellelike leap. Harvey, who retired from the ABT in 1997, was known for those jumps; she had a great “hang time,” although neither she nor any other jumper ever really hangs, Laws notes. Once the dancer leaves the floor, she is like a ballistic missile: Her center of gravityfollows a fixed parabola. She can’t change that, but she can move parts of her body. By scissoring her legs open as she nears the top of the arc and then closing them again as she descends, she makes them take up most of her center of gravity’s vertical motion. For that instant, her head and torso can actually move horizontally. Spectators focus on those parts and think the whole dancer is floating.
The fouetté turn, a full understanding of which struck Laws like a whip late one night, creates a different illusion: perpetual motion. It is a seemingly endless series of pirouettes on one pointed foot—32 in a row, in one passage of Swan Lake—each punctuated by a tiny pause in which the dancer spreads her arms and faces the audience. All the while, her other leg keeps whipping through the air nonstop. What that leg is doing, Laws realized, is storing momentum. During each pause the dancer regains momentum by coming down off point and pushing again with her whole supporting foot. But by keeping the other leg in rotation, she saves some momentum from one turn to the next. To store momentum in the leg she kicks it straight out, far from her spin axis, as she faces the audience; to transfer momentum back to her body she tucks the leg back in as she faces away. The whole thing is fluid and physically sensible, beautiful and economical. When Laws understood this, he jumped out of bed and started fouetté-ing around the room.