Before trying a grand jeté en tournant, there are a couple of things you should know. First, forget about starting your turn in midair, as some ballet teachers might instruct you. To turn your body you must apply a torque, or twisting force, to it, and once you're in the air you have nothing to apply a torque with. If, on the other hand, you begin twisting from the ground up, clasping your legs together at the apex of your leap while raising your arms above your head, you will do a rapid 180-degree turn, which is the object of the exercise. "That's physics," says Ken Laws. Laws is a professor of physics at Dickinson College in Carlisle, Pennsylvania. He also has a very serious case of balletomania.