Some skilled basketball players seem to hang in midair during a jump at the basket, allowing them more time to shift the ball from hand to hand and then into the basket. Similarly, some skilled ballet performers seem to float across the stage during the leap known as a grand jeté. Obviously no one can turn off gravitation during a jump or a leap, so what accounts for these two examples of apparent hanging in midair?

Answer The hang-in-midair of both basketball player and ballet performer is an illusion. In basketball the illusion is primarily due to a player’s agility to perform so many maneuvers during the jump. In ballet’s grand jeté, the illusion comes from a shift of the performer’s arms and legs during the leap: She raises her arms and stretches her legs out horizontally as soon as her feet leave the stage. These actions shift her center of mass upward through her body (Fig. 1-11). Although the center of mass faithfully follows a (curved) parabolic path across the stage as required by gravitation, its movement relative to the body decreases the height that would have been reached by the head and torso in a normal leap. The result is that the head and torso follow a nearly horizontal path during the middle of the leap. This path seems strange to the audience who, out of normal experience, expect a parabolic path even if they do not even know the term.

FIGURE 1-11    / Item 1.35 Path of the center of mass during a grand jeté.

A basketball player can similarly flatten the path taken by the head during a jump across the floor if the player pulls up the legs and raises up the arms and ball. However, I don’t think that this technique is commonly planned by players. Although a player raises the arms and ball toward a basket during a jump near the basket, a player rarely lifts the legs, and the resulting slight flattening of the path taken by the head hardly seems to fool a defensive player who jumps alongside the shooting player.