extended at the hips, which demonstrates that they are able to generate rotation from the takeoff edge and from their entire body instead of relying on their arms. It also demonstrates their back strength and technical ability to complete the rotation without relying on their arms. Unusual entries into jumps demonstrate that skaters are able to control both the jump and, with little preparation, the transition from the previous move to the jump. Skaters rotate more quickly when their arms are pulled in tightly to their bodies, which requires strength to keep their arms being pulled away from their bodies as they rotate. According to scientist Deborah King from Ithaca College, there are basic physics common to all jumps, regardless of the skating techniques required to execute them. Factors such as angular momentum, the moment of inertia, angular acceleration, and the skater's center of mass determines if a jump is successfully completed. Unlike jumping from dry land, which is fundamentally a linear movement, jumping on the ice is more complicated because of angular momentum. For example, most jumps involve rotation. Scientist James Richards from the University of Delaware says successful jumps depend upon "how much angular momentum do you leave the ice with, how small can you make your moment of inertia in the air, and how much time you can spend in the air". Richards found that a skater tends to spend the same amount of time in the air when performing triple and quadruple jumps, but their angular momentum at the start of triples and quadruples is slightly higher than it is for double jumps. The key to completing higher-rotation jumps is how they control the moment of inertia. Richards also found that many skaters, although they were able to gain the necessary angular momentum for takeoff, had difficulty gaining enough rotational speed to complete the jump. King agrees, saying skaters must be in the air long enough, have enough jump height to complete the required revolutions, and the amount of vertical velocity they are able to gain as they jump off the ice, although different jumps require different patterns of movement. Skaters performing quadruple jumps tend to be in the air longer and have more rotational speed. King also found that most skaters "actually tended to skate slower into their quads as compared to their triples", although the differences in the speed in which they approached triples