首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
When you watch a football game on a Saturday afternoon, you feel secure in your knowledge of what will happen when a player boot
When you watch a football game on a Saturday afternoon, you feel secure in your knowledge of what will happen when a player boot
admin
2011-02-26
62
问题
When you watch a football game on a Saturday afternoon, you feel secure in your knowledge of what will happen when a player boots the ball. It first goes up and then it comes down. That’s how it is, was, and will be--unless.... if the kicker someday should kick the ball such that at the instant it left his toe it were travelling upward at a rate of 11.2 kilometers per second (25 000 mhr). We would find that we would not have to worry about a punt return, because the ball simply would not come down. This particular speed is the escape velocity of an object from the earth. At this speed, any object, large or small, will escape from the earth to soar forever upward until captured by the gravitational attraction of some other planet or heavenly body. At first thought it might seem that a heavy object might require a greater initial speed to escape from the surface of the earth than a lighter one, remember that the way objects fall (or move upward against gravity) is independent of the mass of the object. As a result, if a velocity of 11.2 kilometers per second is enough to cause a football to escape from the earth, it is also enough to send a bowling ball (or a freight car) on its way.
The concept of escape velocity applies to objects as small as atoms and molecules. The earth’s atmosphere is composed primarily of oxygen and nitrogen, and it contains practically no trace of hydrogen or helium, the lightest elements. All the atoms of a gas travel in random motion at very high speeds, and the less massive atoms and molecules travel at the greatest speeds. In fact, the lighter gases go so fast that their speeds are greater than the critical speed of 11.2 kilometers per second. Thus they have long ago left our comfortable home and are now wandering through space in search of a more hospitable gravitational field.
The moon has a weaker gravitation field than the earth. The escape velocity of an object on the moon is about 2.4 kilometers per second, and even the heavier gases have enough speed to escape the moon. This explains why we find no atmosphere there; any gases that may be released near the moon quickly escape.
Only when a ball exceeds 11.2 km’ per second can it ______.
选项
A、reach other planets
B、make a goal
C、escape from the earth
D、go upwards
答案
C
解析
转载请注明原文地址:https://kaotiyun.com/show/ZCBO777K
0
考博英语
相关试题推荐
•Lookatthelistbelow.Itshowssomeofnon-fictioncategories.•Forquestions6-10,decidewhichsection(A-H)ofthecat
Allspeakersproducesummariesofthesessionstheygave.Thespeakersshouldwrite______.
ThemilitaryaspectoftheUnitedStatesCivilWarhasalwaysattractedthemostattentionfromscholars.Theroarofgunfire,t
TheBasisforSocialOrderMan,saidAristotle,isasocialanimal.Thissociabilityrequirespeacefulcongregation,andthe
Thegangderivedtheirnicknamefromtheirdarkclothingandblackedupfacesfornocturnalraidsintheforest.
Therehavebeenseveralattemptstointroducegayercolorsandstylesinmen’sclothing,butnoneofthem______.
Thegangderivedtheirnicknamefromtheirdarkclothingandblackedupfacesfornocturnalraidsintheforest.
BrazilianmusicisthoroughlyimbuedwithAfricanthemes,andillustriouscomposershavelongfoundinspirationintheblackmus
Mostenvironmental______fromclimatechangestofreshwaterandforesthabitatlosshavebecomemarkedlyworse.
Standardusageincludesthosewordsandexpressionsunderstood,used,andacceptedbyamajorityofthespeakersofalanguage
随机试题
不从众分为三种情况:()、()、()。
阅读《季氏将伐颛臾》中的一段文字,然后回答小题。孔子曰:“求!周任有言曰:‘陈力就列,不能者止。’危而不持,颠而不扶,则将焉用彼相矣?且尔言过矣,虎兕出于柙,龟玉毁于椟中,是谁之过与?”将“虎兕出于柙,龟玉毁于椟中”译成现代汉语,并说明这两句话的
下列哪项不符合心房颤动的临床表现?
正常足月新生儿。母乳喂养后应取的体位是
男性,42岁,高血压病史5年,近2周自感头痛头晕加重,伴心悸明显。查体:血压180/100mmHg起。ECG示:二度Ⅱ型房室传导阻滞。控制血压不宜选择下列哪项
此建设项目(上题)污水水质复杂程度为()。
根据《最高人民法院关于审理建设工程施工合同纠纷案件适用法律问题的解释》第16条的规定,因设计变更导致建设工程的工程量或者质量标准发生变化,当事人对该部分工程价款不能协商一致的,该如何处理()。
读图文材料。回答问题。天津近、现代工业集聚地经历了由南、北运河与海河交汇处附近→市区海河两岸、铁路沿线→市区边缘→滨海地区、卫星城镇的变化过程。(4)山区农家乐旅游活动吸引城市游客的原因是_______;这种旅游活动对区域文化的积极响是______
幼小衔接
财政专家指出,公共风险不仅产生于因政府政策不当导致的国有资产流失,而且由于政府直接积极参与经济生活,如政府直接参与国有企业,调控金融机构,这些重要经济领域一旦发生大面积损失,将会直接酿成公共风险,从而造成财政赤字、债务偿还压力。因此,如果要想实施稳健的财政
最新回复
(
0
)