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
If a mother pushes her small son in a swing, giving only a light force each time he returns, eventually he will be swinging quit
If a mother pushes her small son in a swing, giving only a light force each time he returns, eventually he will be swinging quit
admin
2013-01-15
67
问题
If a mother pushes her small son in a swing, giving only a light force each time he returns, eventually he will be swinging quite high. The child can do this for himself by using his legs to increase the motion, but both the mother’s push and the child’s leg movements must occur at the proper moment, or the extent of the swing will not increase. In physics, increasing the swing is increasing the amplitude; the length of the rope on the swing determines its natural oscillation period. This ability of an object to move periodically or to vibrate when stimulated by a force operating in its natural period is called resonance.
Resonance is observed many times without consciously thinking about it; for example, one may find an annoying vibration or shimmy in an automobile, caused by a loose engine mount vibrating with increasing amplitude because of an out-of-round tire. The bulge on the tire slaps the pavement with each revolution; at the natural resonance point of the engine mount, it will begin to vibrate. Such vibrations can result in considerable damage if allowed to persist. Another destructive example of resonance is the shattering of a crystal goblet by the production of a musical tone at the natural resonant point of the goblet. The energy of the sound waves causes vibration in the glass; as its amplitude increases, the motion in the glass exceeds the elasticity of the goblet, and it shatters.
An instrument called a tachometer makes use of the principle of resonance. It consists of many tiny bars, loosely fastened together and arranged so that each bar can slide independently of the others. Movement of the bars causes changes in a dial. When placed next to a rotating motor or engine, the tachometer picks up slight vibrations which are transferred to the resonant bars. These bars begin to move, and the resulting dial may be read to find the revolutions per minute of the motor very quickly.
An annoying vibration can be caused at the natural resonance of the car’s engine mount ______.
选项
A、if the engine moves too fast
B、if the engine’s amplitude increases
C、if a tire gets out of balance
D、if a damage occurs in the engine
答案
C
解析
转载请注明原文地址:https://www.kaotiyun.com/show/Nn2O777K
0
考博英语
相关试题推荐
Officerevolution(notonly)haschanged(how)workisdonebut(redefined)thefunctionofeveryonewho(works)inanoffice.
(Nottoomany)years(ago)mymotherjoggedinthealleybehindourhousebecauseshewasembarrassed(tosee)jogging(inpubli
Howdoesithappenthatchildrenlearntheirmothertonguesowell?Whenwecomparewithadultslearningaforeign11.______
Howdoesithappenthatchildrenlearntheirmothertonguesowell?Whenwecomparewithadultslearningaforeign11.______
Howdoesithappenthatchildrenlearntheirmothertonguesowell?Whenwecomparewithadultslearningaforeign11.______
Inacarengine,more______.meansbetteracceleration.
【66】Astateuniversitypresidentwasarrestedtodayandchargedwithimpersonateapoliceofficerbecame,theauthoritiessay,h
Withmostonlinerecruitmentservices,jobseekersmustchoosetheirwordscarefully;______thesearchenginewillnevermaketh
Thecells(电池)weredesignedto______sunshinetoelectricitytorunamotor.
随机试题
习主席指出,军事科学研究具有很强的探索性,要把创新摆在更加突出的位置,做好战略谋划和顶层设计,加强军事理论创新、国防科技创新、军事科研工作阻止模式创新,把军事科研创新的引擎全速发动起来。国防科技工业施行的方针不包括()。
_________一般是指商业银行接受的客户以现金方式存入的存款和中央银行对商业银行的资产业务而形成的准备金存款。
慢性胃炎最常见的临床表现是()
A.加减葳蕤汤B.桂枝汤C.香薷散D.柴葛解肌汤E.升麻葛根汤功用为解肌清热的方剂是
以下哪个区域应列为缓冲区
金融机构必须依法合规收集保存使用和对外提供个人金融信息,这些法律、法规、规章和规范性文件是()。①《中华人民共和国商业银行法》②《个人存款账户实名制规定》③《个人信用信息基础数据库管理暂行办法》④《中国人民银
在一个和弦发响的自始至终,任何一个声部中出现的该和弦结构以外的音,称为(),可笼统地用“+”标记。
在市场经济条件下,企业要想达到自身获利的目的,必须首先生产或提供对他人有价值的东西。如果企业置他人利益于不顾,采取欺骗的手段进行不正当交换,不仅不被社会容忍,而且要受到法律惩罚。市场经济内在地要求企业遵循诚信、公平、负责等交换准则。这些交换准则,内含着维系
赵、钱、孙、李4人涉嫌某案被传讯。赵说:作案者是钱。钱说:作案者是赵。孙说:作案者是我。李说:作案者在我们4人中。如果4人中有且只有一个说真话,则以下哪项断定成立?
我国刑法规定,对犯罪集团的首要分子的处罚原则是()。
最新回复
(
0
)