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
The prefix Mach is used to describe supersonic speed. It was named for Ernst Mach (1838—1916), a Czech-born Austrian physicist,
The prefix Mach is used to describe supersonic speed. It was named for Ernst Mach (1838—1916), a Czech-born Austrian physicist,
admin
2014-09-18
18
问题
The prefix Mach is used to describe supersonic speed. It was named for Ernst Mach (1838—1916), a Czech-born Austrian physicist, who contributed to the study of sound. When twice the speed of sound, it is Mach 2. When it is near but below the speed of sound, its speed can be designated at less than Mach 1, for example, Mach 0. 90. Mach is defined as "the ratio of the velocity of a rocket or a jet to the velocity of sound in the medium being considered".
When a plane passes the sound barrier — flying faster than sound travels, listeners in the area hear thunderclaps, but the pilot of the plane does not hear them.
Sound is produced by vibrations of an object and is transmitted by alternate increase and decrease in pressure that radiate outward through a material media of molecules — somewhat like waves spreading out on a pond after a rock has been tossed into it.
The frequency of sound is determined by the number of times the vibrating waves undulate per second and is measured in cycles per second. The slower the cycle of waves, the lower the frequency. As frequencies increase, the sound is higher in pitch.
Sound is audible to human beings only if the frequency falls within a certain range. The human ear is usually not sensitive to frequencies of fewer than 20 vibrations per second, or more than about 20, 000 vibrations per second — although this range varies among individuals. Anything at a pitch higher than the human ear can hear is termed ultrasonic.
Intensity, or loudness, is the strength of the pressure of these radiating waves and is measured in decibels. The human ear responds to intensity in a range from zero to 120 decibels. Any sound with pressure over 120 decibels is painful to the human ear.
The speed of sound is generally placed at 1, 088 feet per second at sea level at 32 degrees Fahrenheit. It varies in other temperatures and in different media. Sound travels faster in water than in air, and even faster in iron and steel. It travels a mile in 5 seconds in air, it does a mile under water in 1 second, and it travels through iron in 1 /3 second. It travels through ice cold vapor at approximately 4, 708 feet per second; ice-cold water, 4,938; granite, 12,960; hardwood, 12,620; brick, 11,960, glass, 16,410 to 19,690; silver, 8,658; gold, 5,717.
According to this passage, "Mach" refers to
选项
A、the ratio of the air speed of an aircraft to the speed of sound.
B、a machine.
C、a Czech-born Australian physicist.
D、the pilot of the plane.
答案
A
解析
第一段提到了Mach的相关信息,其中最后一句提到,马赫(Mach)是火箭或飞机在空中的速度与声速的比率,由此可知答案为[A]。
转载请注明原文地址:https://jikaoti.com/ti/3pxMFFFM
0
专业英语四级
相关试题推荐
InAmericaalone,tippingisnowa$16billion-a-yearindustry.Arecentpollshowedthat40%ofAmericans(1)______thepractic
Educationofexceptionalchildrenmeansprovisionofspecialeducationalservicestothosechildrenwhoareeitherhandicappedo
Cultureinfluencesanindividual’shealthbeliefs,behaviours,activitiesandmedicaltreatmentoutcomes.(1)______thesignifica
Cultureinfluencesanindividual’shealthbeliefs,behaviours,activitiesandmedicaltreatmentoutcomes.(1)______thesignifica
Foralongtime,newspapershavebeenthechiefmeansbywhichpeoplegetthemselves(1)______.Thenewspapers,daily,evening,a
Theuseofnitrousoxide,orlaughinggasduringchildbirthfelloutoffavorintheUnitedStatesdecadesago,andjusttwohos
Iwenttherein1984,andthatwastheonlyoccasionwhenI______thejourneyinexactlytwodays.
FredandBettyfinallydecidedtotietheknot.Theunderlinedpartmeans______.
Yesterdaymyauntboughtsomenew______forherflatattheseaside.
I’dliketo______100dollarsfrommysavingsaccountandputitinmychequeaccount.
随机试题
《风波》的中心线索是【】
在激光的产生过程中,光学谐振腔的作用是
A.长期慢性咳嗽、咳痰或喘息史B.乏力、呼吸困难,活动后加重C.心尖区第一心音增强D.肺动脉瓣区第二心音亢进E.三尖瓣区收缩期杂音和剑突下搏动右心室扩大的主要表现是
根据《水法》规定,在国家确定的重要江河、湖泊上建设水工程,建设单位在工程开工前,()应当对水工程的建设是否符合流域综合规划进行审查并签署意见。
A单位与B单位没有合同关系,A单位与C单位签有供货合同,由于D单位的银行账号与C单位的相似,A单位将应打入C单位银行账号的一笔资金误打入了B单位银行账号,B单位将这笔资金据为已有。B单位的这一行为属于()。
会计报表附注是为了会计报表使用者便于理解会计报表的内容而对会计报表所作的解释,以下属于其内容的是()、
有些学生的家长让学生戴一种新型手表。这种手表能把学生得位置实时传输给家长。并在家长手机的电子地图上显示出来。这种手表运用得技术是()。①RS②GPS③GIS
我国第一部文学理论专著是()。
民警违反规定使用枪支致人死亡的,对所在单位直接领导()。
下列特征中不是面向对象方法的主要特征的是()。
最新回复
(
0
)