时间:2019-01-26 作者:英语课 分类:英语听力文摘 English Digest


英语课

   Remember seesaws 2? Those things were great. But there was often a problem.


 
  Suppose there’s a big kid on one side and a smaller kid on the other side. The seesaw 1 just stays in one position: big kid on the ground, smaller kid up in the air. No fun. After a few different tries, you probably realized that moving the big kid in toward the center made it possible to rock a little. Move the big kid even more and you can achieve balance. Now the seesaw works.
 
  What’s going on here? The answer is in the “center of mass.” The center of mass is a point somewhere along the plank 3 that holds the two kids where their average weight falls. If you can get the center of mass to be over the pivot 4 point, the seesaw will be balanced.
 
  There’s a simple way to figure out where the center of mass is. If the big kid is two times as heavy as the little kid, then their mutual 5 center of mass will be two times closer to the big kid than to the little kid. Three times heavier and the center of mass will be three times closer. And so on.
 
  So the reason the heavy kid sits on the ground while the light kid is up in the air is that their mutual center of mass is on the heavy kid’s side of the pivot. To make the seesaw work, the heavy kid must push that center of mass forward until it just touches the pivot. Then their average weight pushes right on the middle, letting the ends rock up and down.
 
  还记得跷跷板吗?它可是伟大的发明,但仍然存在一个问题。
 
  假设跷跷板的一边坐一个大点的孩子,而另一边坐一个 小点的孩子。跷跷板就只停留在一边:大孩子那边,小孩子则悬在空中。这样就失去了跷跷板的乐趣。几次尝试后,你也许会发现让大孩子往中间坐久可以摇动一点。再让大孩子让中间挪动直至平衡后跷跷板就可以摇动了。
 
  这到底是怎么回事?答案就是“质心”。质心是跷跷板上支撑两个孩子平均重量的一个点。如果找到了是新的支点,跷跷板就平衡了。
 
  有一个简单的方法找出质心。如果大孩子的重量是小孩子的2倍,那么质心的位置离大孩子的距离就比离小孩子距离近2倍。重三倍,质心的位置就进三倍,以此类推。
 
  因此,重的小孩坐在地上而轻的小孩悬在空中的原因是,他们共同的质心在重的孩子这边。要想让跷跷板摇动,重的孩子就得往中间挪直到质心移到中心。然后当他们的平均质量正好在中间,这样两头就可以上下摇动了。

n.跷跷板
  • Prices have gone up and down like a seesaw this year.今年的价格像跷跷板一样时涨时跌。
  • The children are playing at seesaw.孩子们在玩跷跷板。
n.跷跷板,上下动( seesaw的名词复数 )v.使上下(来回)摇动( seesaw的第三人称单数 );玩跷跷板,上下(来回)摇动
n.板条,木板,政策要点,政纲条目
  • The plank was set against the wall.木板靠着墙壁。
  • They intend to win the next election on the plank of developing trade.他们想以发展贸易的纲领来赢得下次选举。
v.在枢轴上转动;装枢轴,枢轴;adj.枢轴的
  • She is the central pivot of creation and represents the feminine aspect in all things.她是创造的中心枢轴,表现出万物的女性面貌。
  • If a spring is present,the hand wheel will pivot on the spring.如果有弹簧,手轮的枢轴会装在弹簧上。
adj.相互的,彼此的;共同的,共有的
  • We must pull together for mutual interest.我们必须为相互的利益而通力合作。
  • Mutual interests tied us together.相互的利害关系把我们联系在一起。
学英语单词
adovetine
advocacy tank
aerophoto interpretation
agonist
all the way to
allergic rhinitis
ancient coast zone
Arviat
As affairs stand
Baol
base apex line
basic frame-handling function
bicycle ergonometer
blade homogenizer
cathode-ray scan display
CCK-27-32-amide
CF (cost and freight)
chainline
convergent homeomorpha
correr
Corumo, R.
d-tylocrebrine
DFTT
disci ovigerus
disruptive pattern
dome of the second order
Draguseni
employee ownership
entente cordiale
fineers
flattening off
flirtinis
functional writing
grid formation
hemibasidia
herballs
hierarchical basis
high bridge knitting machine
hoggan-bag
hyper-eutectic
instrumental pelvimetry
intracytosis
johnies
JTOL
jungkook
la nina phenomenon
Le Sage
leapfrog integration scheme
legal tender powers
lightmindedness
LLLNR
lubricating grease
marisse
mealy plum aphid
mid-career scholar
molapoes
northern blot analysis
off-the-peg
ognissantis
oje
one-by-one feeding
ovolactarian
oxidational losses
Paddy's hurricane
palel
pathogeography
pharyngologist
point spread function
port st. lucie
ppbv
putrefactivebacteria
reference wind speed
rotating floor
Santo Domingo, Cerro
serviceability testing
shamers
shingless
signs of wear
simplex mode
slope curve
smoke consuming apparatus
soft arbitrage
solar system
special appropriation
specimen tube of hot pressure stress
spider crabs
tangential method
tender report
top bench
trace system
Triftern
underdosed
upper photic zone
Vamberk
Vanda cristata
vector boson
volitionalism
Volochayevskiy
Wang Saphung
warm-pressing
West Coast Bajau
worm driven rear axle