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
63
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
YouwillhearabankconversationbetweenadepartmentdirectorSteveandanewcustomerHansa.Foreachquestion(23-30),ma
Lookatthenotesbelowaboutacompany’splansforshoespromotionthisspring.Someinformationismissing.Youwillh
•YouarepersonalassistanttothepresidentofanAmericantradingcompany,DNLInternational.Thepresidentleavesyouamem
Allspeakersproducesummariesofthesessionstheygave.Thespeakersshouldwrite______.
TipstoIncreaseRetailSalesGenerateaBuzz—Wheneveranythingnoteworthyhappenswithinyourbusiness,sendapressreleas
TheBasisforSocialOrderMan,saidAristotle,isasocialanimal.Thissociabilityrequirespeacefulcongregation,andthe
(Tobemeasured)intermsofitsmembers,teachingis(theworld’sbiggestprofession).Thoughtherolesandfunctionsofteache
Distinguishedarchitecturerequirestheexpenditureoflargesumsofmoney,evenifitisbynomeanscertain______theexpendi
Mostenvironmental______fromclimatechangestofreshwaterandforesthabitatlosshavebecomemarkedlyworse.
Manhasbecomemasteroftheearth’ssurface.Heisconstantlyprobingintotheearth’sdepthsandintotheatmosphere’suppe
随机试题
我国推动建立的新型国际关系,“新”在()
抢救大咯血窒息患者时最紧急的措施是
Graves病是自身免疫性疾病,下列哪项概念是错误的
三阴交位于
下列关于热拌热铺沥青混合料路面试验段试验内容的说法,正确的有()。
球罐焊接完后应立即进行焊后热处理,其主要的目的有()。
会计职业道德只具有很强的他律性。()
ISO 9000资质认证过程中要对企业的各方面进行严格审查,还要每年进行自检和外检。ISO 9000质量管理体系认证书的有效期为(7)。
假设在DAT为首地址的连续三个字单元中存放一个48位的数,问下面的程序段中第二条指令应填入什么助记符才能使该明位数左移一个二进制位? SAL DAT,1 _____DAT+2,1 RCL DAT+4,1
IfthepubliclibrarysharedbytheadjacenttownsofRedvilleandGlenwoodwererelocatedfromthelibrary’scurrent,overcrowd
最新回复
(
0
)