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
2014-07-20
27
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 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 1088 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.
Decibel is
选项
A、the unit for measuring the4ntensity of sound.
B、the pressure of radiating waves.
C、the frequency of radiating waves.
D、the speed of sound.
答案
A
解析
根据第六段第一句“分贝是用来测量声音强度或大小的,即测量音量的单位”,故答案为A 。
转载请注明原文地址:https://kaotiyun.com/show/THTK777K
0
专业英语四级
相关试题推荐
Asvisitingscholars,theywillingly______tothecustomsofthecountrytheylivein.
Myclassmatesstoodtherelookinguneasilyatme,puzzlingwhyIhadn’tgotannoyedthistimewhenIcouldn’tgetmyown______.
IwasborninTuckahoe,TalbotCountry,Maryland.Ihavenoaccurateknowledgeofmyage,neverhavingseenanyauthenticreco
IwasborninTuckahoe,TalbotCountry,Maryland.Ihavenoaccurateknowledgeofmyage,neverhavingseenanyauthenticreco
Federaleffortstoaidminoritybusinessesbeganinthe1960’swhentheSmallBusinessAdministration(SBA)beganmakingfederal
Thearrivalofthemass-producedcar,justoveracenturyago,causeda(n)(1)_____ofbusinesscreation.Firstcamethemakerso
Insomecountries,societalandfamilialtreatmentoftheelderlyusuallyreflectsagreatdegreeofindependenceandindividual
Iwasimpressedbytherangeof______accessoriesofmymicrocomputerthatwereavailable.
Thepolicehaveofferedalarge______forinformationleadingtotherobber’sarrest.[2002]
Evidenceofthebenefitsthatvolunteeringcanbringolderpeoplecontinuestorollin."Volunteershaveimprovedphysicalands
随机试题
下列有关肺总量的叙述,哪一项是错误的?
关于卵巢肿瘤,下列描述不正确的是
对恶性胸水定性诊断最有帮助的是
刚性防水屋面的防水层应设置分格缝,且其纵横间距不宜大于6m,下列哪项的设置是不必要的?[2001年第073题]
在图4-74中,将圆环的惯性力系向O点简化,其主矢F1和主矩MIO的数值为()。
空气净化设备常用的吸收剂有()。
在下列项目中,同复合杠杆系数成正方向变动的有( )。
简要叙述信息系统项目管理的重要环节?
下列有关合并范围确定的表述中,符合企业会计准则规定的有()。
下列有关艾滋病(AIDS)的叙述,错误的是()。
最新回复
(
0
)