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 downward 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 height of any 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 way to achieve higher jumps and increase hang 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 jumps called a grand jete, a skillful ballet dancer seems to float fro 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 curved path a ball takes when you throw it into the air. So do dancers make it look like they're hanging in the air?
A dancer creates the illusion of floating in the air by lifting her legs and arms as she approaches the peak of the jump. The rest 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 not only beautiful; it also 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 off 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, body carries with it momentum. Momentum is the weight of the body multiplied by its speed. 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 opposing force-the ground. Landing can be very jarring to a dancer and can cause injuries. The dancer can ease the landing by needing 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 like shock absorbers. They are springy and can recoil as mush as an 9ch under extreme pressure. That little bit of give makes a big difference. 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 gradually with less force and less chance of injury. [理工類A]
縱身一躍
在許多不同風格的舞蹈表演中，跳躍都是很關鍵的一項。一般說來，讓一個跳躍動作精彩的因素不在于它的停留時間，即舞者在空中停留的時間。
追求更長的空中停留時間實際上是和重力的一場較量，重力是地球對你往下拉的力量，要整個身子都脫離地面。舞者必須用腿部肌肉的力量創(chuàng)造出一個比重力更大的向上的沖力。但是最后的高度只取決于一件事，即舞者脫離地面向上跳時的速度大小。
一種用來達到跳得更高，空中停留時間更長的很明顯的做法是通過加強肌肉以使它能更有強度地推動身體往上跳。但是芭蕾舞蹈演員也用一種小小的又很簡單的技巧來制造一種停留空中很長時間的假象，但實際上他們并沒停留多長時間。
在一種大幅度的側身跳躍動作（小跳）中，一個技藝精湛的芭蕾舞演員好像在空中可以停上一段讓人難以置信的時間。當然，一個舞者不可能真正地在空中懸著的。物理學中的定理規(guī)定了在任何一種跳躍中，一個舞者的重心是循著一條拋物線的軌跡走的。一條拋物線就如同一個你隨手扔去的球所經(jīng)過的路線。但是一個舞者如何做到使他們看起來像是在空中懸著的呢？
一個舞者在她達到跳躍過程中處時伸展她的雙腿和雙臂，從而創(chuàng)造了一個停在空中的幻覺。她身體的其他部分如軀干和頭部則相應地下沉一點。如果時間控制得好，她就會看起來像是側面浮在空中，而不是上升或下降，所產(chǎn)生的效果則不僅僅是漂亮的動作，而且也使這跳躍看起來更大，因為它在跳得的時候“伸展”開了。
當然，不可否認的是，跳上去就必定得落下來。在一個標準的芭蕾舞小跳動作中，舞者的重心躍到離地2英尺的高處。在這樣的高度受重力拉動，她的身體將以每秒約3.4米的速度往下墜。在下落的過程當中，身體是帶有動量的。一個人的動量的大小是體重和速度的乘積值表示的。體重越大，下落的速度越快，動量就越大。
舞者要阻止從空中掉落的惟一方法便是中止自己的動量，而這需要一個反面的來自一個平面的阻力。對舞蹈演員來說，落地會產(chǎn)生很大的反彈力，也有可能因此受傷。舞蹈演員可能以通過屈膝和放下手臂來對落地來一下緩沖，但她同時也可以得到地面這意想不到的幫助。木制的舞蹈地板被設計成像是震動吸收者。它們有彈性，可以后縮，在非常大的壓力之下可以后縮到一英寸。這么一個小小的彈性產(chǎn)生的作用可不小。舞蹈演員如果落在有彈性的地板上將使動量變化過程比落在一塊硬地上的要慢。這個彈力使動量減少的過程更為緩慢，因而只帶有較少的沖擊力和受傷的幾率。[理工類A]
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 downward 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 height of any 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 way to achieve higher jumps and increase hang 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 jumps called a grand jete, a skillful ballet dancer seems to float fro 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 curved path a ball takes when you throw it into the air. So do dancers make it look like they're hanging in the air?
A dancer creates the illusion of floating in the air by lifting her legs and arms as she approaches the peak of the jump. The rest 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 not only beautiful; it also 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 off 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, body carries with it momentum. Momentum is the weight of the body multiplied by its speed. 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 opposing force-the ground. Landing can be very jarring to a dancer and can cause injuries. The dancer can ease the landing by needing 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 like shock absorbers. They are springy and can recoil as mush as an 9ch under extreme pressure. That little bit of give makes a big difference. 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 gradually with less force and less chance of injury. [理工類A]
縱身一躍
在許多不同風格的舞蹈表演中，跳躍都是很關鍵的一項。一般說來，讓一個跳躍動作精彩的因素不在于它的停留時間，即舞者在空中停留的時間。
追求更長的空中停留時間實際上是和重力的一場較量，重力是地球對你往下拉的力量，要整個身子都脫離地面。舞者必須用腿部肌肉的力量創(chuàng)造出一個比重力更大的向上的沖力。但是最后的高度只取決于一件事，即舞者脫離地面向上跳時的速度大小。
一種用來達到跳得更高，空中停留時間更長的很明顯的做法是通過加強肌肉以使它能更有強度地推動身體往上跳。但是芭蕾舞蹈演員也用一種小小的又很簡單的技巧來制造一種停留空中很長時間的假象，但實際上他們并沒停留多長時間。
在一種大幅度的側身跳躍動作（小跳）中，一個技藝精湛的芭蕾舞演員好像在空中可以停上一段讓人難以置信的時間。當然，一個舞者不可能真正地在空中懸著的。物理學中的定理規(guī)定了在任何一種跳躍中，一個舞者的重心是循著一條拋物線的軌跡走的。一條拋物線就如同一個你隨手扔去的球所經(jīng)過的路線。但是一個舞者如何做到使他們看起來像是在空中懸著的呢？
一個舞者在她達到跳躍過程中處時伸展她的雙腿和雙臂，從而創(chuàng)造了一個停在空中的幻覺。她身體的其他部分如軀干和頭部則相應地下沉一點。如果時間控制得好，她就會看起來像是側面浮在空中，而不是上升或下降，所產(chǎn)生的效果則不僅僅是漂亮的動作，而且也使這跳躍看起來更大，因為它在跳得的時候“伸展”開了。
當然，不可否認的是，跳上去就必定得落下來。在一個標準的芭蕾舞小跳動作中，舞者的重心躍到離地2英尺的高處。在這樣的高度受重力拉動，她的身體將以每秒約3.4米的速度往下墜。在下落的過程當中，身體是帶有動量的。一個人的動量的大小是體重和速度的乘積值表示的。體重越大，下落的速度越快，動量就越大。
舞者要阻止從空中掉落的惟一方法便是中止自己的動量，而這需要一個反面的來自一個平面的阻力。對舞蹈演員來說，落地會產(chǎn)生很大的反彈力，也有可能因此受傷。舞蹈演員可能以通過屈膝和放下手臂來對落地來一下緩沖，但她同時也可以得到地面這意想不到的幫助。木制的舞蹈地板被設計成像是震動吸收者。它們有彈性，可以后縮，在非常大的壓力之下可以后縮到一英寸。這么一個小小的彈性產(chǎn)生的作用可不小。舞蹈演員如果落在有彈性的地板上將使動量變化過程比落在一塊硬地上的要慢。這個彈力使動量減少的過程更為緩慢，因而只帶有較少的沖擊力和受傷的幾率。[理工類A]