首页
登录
职称英语
The gravitational pull of the Earth and moon is important to us as we attemp
The gravitational pull of the Earth and moon is important to us as we attemp
游客
2025-05-09
29
管理
问题
The gravitational pull of the Earth and moon is important to us as we attempt to conquer more and more of outer-space. Here’s why.
As a rocket leaves the Earth, the pull of the Earth on it becomes less and less as the rocket roars out into space. If you imagine a line between the Earth the pull of the Earth and the moon, there is a point somewhere along that line, nearer to the moon than to the Earth, at which the gravitation pull of both the Earth and the moon on an object is just about equal. An object placed on the moon side of that point would be drawn to the moon. An object placed on the Earth side of that point would be drawn to the Earth. Therefore, a rocket need be sent only to this "point of no return" in order to get it to the moon. The moon’s gravity will pull it the rest of the way.
The return trip of the rocket to Earth is, in some ways, less of a problem. The Earth’s gravitational field reaches far closer to the moon than does the moon’s to Earth. Thus it will be necessary to fire an Earthbound rocket only a few thousand miles away from the moon to reach a point where the rocket will drift to earth under the Earth’s gravitational pull.
The problem of rocket travel is not so much concerned with getting the rocket into space as it is with guiding the rocket after it leaves the Earth’s surface. Remember that the moon is constantly circling the Earth. A rocket fired at the moon and continuing in the direction in which it was fired would miss the moon by a wide margin and perhaps continue to drift out into space until "captured" in another planet’s gravitational field. To reach the moon, a rocket must be fired toward the point where the moon will be when the rocket has traveled the required distance. This requires precise calculations of the speed and direction of the rocket and of the speed and direction of the moon.
For a rocket to arrive at a point where the moon’s gravity will pull it the rest of the way, it must reach a speed called velocity of escape. This speed is about 25,000 miles per hour. At a speed less than this, a rocket will merely circle the Earth in an orbit and eventually fall back to Earth. [br] Precise calculations are ______.
选项
A、good guesses
B、simple problems
C、big errors
D、exact
答案
D
解析
文中的precise的意思是“精确的,准确的”,D项exact“精确的,准确的”与之相符。
转载请注明原文地址:https://tihaiku.com/zcyy/4068324.html
相关试题推荐
Animportantobjectiveofbothexercisesistodevelopastructureforrigorousl
ThegravitationalpulloftheEarthandmoonisimportanttousasweattemp
ThegravitationalpulloftheEarthandmoonisimportanttousasweattemp
ThegravitationalpulloftheEarthandmoonisimportanttousasweattemp
Theballadandthefolksonghavelongbeenrecognizedasimportantkeysto
Hisconstantattemptsto______hiscolleagues’achievementeventuallycausedhi
Thesenationalparksareveryimportantforpreservingmanyanimals,whowouldo
Theirattemptstoevadetaxesturnedouttobefutile.A、intentionsB、ideasC、opi
Thecomingofautomationis______tohaveimportantsocialconsequences.A、like
Animportantcustomermayresentbeing______byanassistantratherthanbythe
随机试题
Francemightbedescribedasan’all-round’country,onethathasachievedr
某高级法院副院长出版了一本刑法学教科书,对刑法的若干问题作了阐释。这种解释属于(
治疗突然昏倒,口噤不开,面青身凉,苔白,脉迟有力,应首选的药物是()A.冰
A.木通B.地肤子C.海金沙D.冬葵子E.绵萆薢善治风湿疹痒的药是
不属于成分输血优点的是()。A.可提高疗效 B.血液使用更合理 C.避
从所给的四个选项中,选择最合适的一个填入问号处,使之呈现一定的规律性:
上海证券交易所目前实行的是上海证券登记结算公司统一托管和证券营业部分别托管的二级
(2020年真题)《商业银行资本管理办法(试行)》中的资本监管要求为()。A.
下列关于年金的说法中,错误的是()。A.年金是一组在某个特定时段内金额相等、
某土方工程业主与施工单位签订了土方施工合同;合同约定的土方工程价款为200万元
最新回复
(
0
)