Making the Leap
Jumps play a big role in many styles of dancing. Generally, what makes a jump impressive is its hang time, the amount of time a dancer spends in the air.
The quest for greater hang time is a battle against gravity, the constant __1__ PULL OF Earth, said Laws. To leave the ground at all, a dancer has to use leg muscles to create an upward push that is greater than Earth’s downward pull. But the final __2__ of any jump depends on just one thing; the upward speed of the body just as the dancer leaves the ground.
Strengthening muscles so they can push harder is one obvious __3__ to achieve higher jumps and increase hand time. But ballet dancers also use a simple trick to gain the illusion of staying in the air longer without actually doing so.
In a huge sideways jump called a grand jets, a __4__ ballet dancer seems to float for an impossible length of time. Of course a dancer can’t really hang in the air. The laws of physics decree that during any jump a dancer’s center of gravity must follow a parabola. A parabola is the same __5__ path a ball takes when you throw it into the air. So how do dancers make it look like they’re hanging in the air?
A dancer __6__ the illusion of floating in the air by lifting her legs and arms as she approaches the peak of the jump. The __7__ of her body — her torso and her head — respond by sinking a bit, If her timing is just right, she’ll seem to float sideways, instead of rising and falling. The effect is no only beautiful; it __8__ makes the jump seem bigger by “stretching out” the peak.
Of course, what goes up must come down. During a typical grand jete, a dancer’s center of gravity rises 2 feet __9__ the ground. Pulled by gravity from such a height, the dancer’s body falls very fast — roughly 3.4 meters per second — by the time it reaches the floor.
As it falls, the body carries with it momentum. Momentum is the weight of the body multiplied by its __10__. The bigger the body is and the faster it falls, the greater its momentum.
The only way a dancer can stop dropping through the air is by stopping the body’s momentum, which requires an __11__ force —the ground. Landing can be very jarring to a dancer and can __12__ injuries. The dancer can ease the landing by bending her knees and letting her arms fall, but she also gets help from an unexpected source: the floor. Wooden dance floors are designed to act __13__ shock absorbers. They are springy and can recoil as much as an inch under extreme pressure. That little bit of give makes a big __14__. Landing on a springy floor, the dancer undergoes a slower change in momentum than she would hitting a rigid floor. The give in the floor allows the decrease in momentum to happen more __15__ —with less force and less chance of injury.
1. A. parallelly B. upward C. sideways D. downward
2. A. center B. height C. weight D. breadth
3. A. street B. road C. way D. passage
4. A. skillful B. beautiful C. careful D. meaningful
5. A. smooth B. short C. curved D. straight
6. A. changes B. uses C. inspects D. creates
7. A. force B. movement C. pull D. rest
8. A. too B. also C. yet D. so
9. A. off B. out of C. along D. onto
10. A. temperature B. speed C. moisture D. time
11. A. rising B. falling C. opposing D. responding
12. A. increase B. cure C. remove D. cause
13. A. like B. love C. protect D. cancel
14. A. sameness B. resemblance C. difference D. nearness
15. A. gradually B. strongly C. spontaneously D. incidentally
责任编辑：虫虫
