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| 声音 |
声音声音是通过物体振动产生的
声音是通过介质（空气或固体、液体）传播并能被人或动物听觉器官所感知的波动现象。
声音是一种压力波：当演奏乐器、拍打一扇门或者敲击桌面时，他们的振动会引起介质——空气分子有节奏的振动，使周围的空气产生疏密变化，形成疏密相间的纵波，这就产生了声波，这种现象会一直延续到振动消息为止。
声音作为波的一种，总可以被分解为不同频率不同强度正弦波的叠加。這種變換（或分解）的過程，稱為傅立葉變換(Fourier Transform)。因此，一般的声音总是包含一定的频率范围。人耳可以听到的声音的频率范围在20到2万赫兹之间。高于这个范围的波动称为超声波，而低于这一范围的称为次声波。
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category:物理学
ja:音
ko:소리
simple:Sound
th:เสียง
介质一种物质存在于另一种物质内部时，后者是前者的介质。
某些波状运动，如声波、光波等，借以传播的物质叫做这些波状运动的介质。
category:力學
固体固体是物质存在的一种状态。与液体和气体相比固体有比较固定的体积和形状、质地比较坚硬。
通过其组成部分之间的相互作用固体的特性可以与组成它的粒子的特性有很大的区别。研究固体的物理科学叫做固体物理学。
一般来说，一个物体要达到一定的大小才能被称为固体，但对这个大小没有明确的规定。一般来说固体是宏观物体，除一些特殊的低温物理学的现象如超导现象、超液现象外固体作为一个整体不显示量子力学的现象。
Category:自然科学
Category:凝聚态物理学
Category:固体物理学
ja:固体
ko:고체
ms:Pepejal
simple:Solid
液体液体是物质存在的一种状态，有比较固定的体积而没有固定的形状，可流动的。增溫或減壓一般能使液體氣化，成爲氣體，例如將水加溫成水蒸氣。加壓或减溫一般能使液體固化，成爲固體，例如將水减溫成冰。然而，仅加压并不能使所有气体液化，如氧，氢，氦等。
Category:凝聚态物理学
ja:液体
ko:액체
ms:Cecair
simple:Liquid
声波本条目种的声波是一个物理学概念，如果要找寻其他有关声波的信息请见声波 (消歧义)
声波是指声音的传播形式。声音由物质振动产生，并以波动的形式在一定的介质中传播。
Category:声学
频率
频率是单位时间内某事件重复发生次数的度量，在物理学中通常以符号 f 表示，其国际单位为赫兹（Hz）。设 t 时间内某事件重复发生 n 次，则此事件发生的频率为 f = n/t 赫兹。又因为週期定义为重复事件发生的最小间隔，故频率也可以週期的倒数表示，即 f = 1/T ，其中 T 表示週期。
在国际标准单位里，频率的单位以德国物理学家海因里希·鲁道夫·赫兹的名字命名。1 Hz 表示事件每一秒发生一次。其他的曾经用来表示频率的单位还有: 周/ 秒, 每分钟转数。心率以1分钟为单位。
计算频率的方法是时间连续发生两次的时间（周期），通过计算时间的倒数得到频率：
:
T表示周期
波的频率
衡量声音、电磁波（例如无线电波或者光）、电信号或者其他波的频率时，表示每秒重复信号波形的数量。如果波是声音，频率就表示音调的特性。
频率与波长成反比例关系。 频率f等于波的速度v除以波的波长λ
:
在真空中电磁波的速度v = c，c是真空中的光速，等式就变成:
:
注意：当波从一中介质进入另一种介质，频率不变，只有波长会变。
举例
- The frequency of the standard pitch tone A above 中央C音 is nowadays set at 440 Hz that is 440 cycles per second (or slightly higher) and known as concert pitch, after which an orchestra is tuned.
- 婴儿能够听到最高频率20,000 Hz的声音，但是成年人却听不到
- 欧洲和中国的交流电频率是50 Hz (接近音调G)，电压是230/220V
- 北美洲使用60Hz (接近音调B平)交流电，额定电压117伏特
参看
波, 周期, 波长, 振幅, 截止频率
音分, 角频率, 简谐运动
音调, 音律, 谐振, 电磁频谱, 琴键频率
频谱
外部链接
- [http://w1.647.telia.com/~u64705175/lista.htm TNFL, The Nordic Frequency List: Extensive collection of Scandinavian frequencies]
Category:物理量
Category:声音
Category:声学
ja:周波数
ko:진동수
th:ความถี่
正弦波正弦信号是频率成分最为单一的一种信号，因这种信号的波形是数学上的正弦曲线而得名。任何复杂信号——例如音乐信号，都可以通过傅里叶变换分解为许多频率不同、幅度不等的正弦信号的叠加。
正弦波的特性
正弦波(sinusoidal wave)為最簡單的週期波，其每一瞬間的波形為正弦或餘弦的函數形狀。介質中各質點未振動時的位置稱為其平衡位置。當波通過時，質點以其平衡位置為中心作簡諧運動。
category:通信技術
赫兹赫兹是国际单位制中频率的单位，它体现每秒中的波的数量。赫兹的名字来自于德国物理学家海因里希·鲁道夫·赫兹。其符号是Hz。
1Hz = 1/s
SI 衍生單位
參看
- 頻率
Category:度量衡
ko:헤르츠
ja:ヘルツ (単位)
次声波频率小于20Hz（赫兹）的声波叫做次声波。某些频率的次声波由于和人体器官的振动频率相近，容易和人体器官产生共振，对人体有很强的伤害性。次声波不容易衰减，不易被水和空气吸收。次声波的波长往往很长，因此能绕开某些大型障碍物发生衍射。某些次声波能绕地球2至3周。
参看
- 声波
- 超声波
- 波
Category:声学
Atrocity
:"Massacre" redirects here. For other uses, see Atrocity (disambiguation)
An atrocity (from the Latin atrox, "atrocious", from Latin ater = "matte black" (as distinct from niger = "shiny black")) is a term used to describe crimes ranging from an act committed against a single person to one committed against a population or ethnic group.
In general use, an atrocity or massacre designates a politically or ethnically motivated killing of civilians. In international law, more precise terms are war crime and crime against humanity.
An atrocity can be a single specific event, or a series of events, or can refer to genocide. The defining characteristic of an atrocity is its brutal or systematic nature. It is an act of killing that is in violation of most traditional moral principles, although some societies do not condemn such behavior. Often, hostilities exceed the legitimate mandate of killing enemy combatants to include attacks upon unarmed people, upon combatants after their surrender, or upon otherwise non-combative peoples. Thus, nearly every culture has in its history acts of killing which are atrocities.
The historical record is clouded by a failure to determine if mutilated bodies represent torture before death, or mutilation of a dead body. In either case, the important effect is the propaganda value, and its effect on the morale of the enemy.
The word "massacre" is sometimes misused in commercial advertisements, e.g. such phrases as "price massacre".
Even massacre, mass killing, is imposed on civilian populations of no military significance, simply as a warning. For example Lidice. In other cases, they are targeted at military sub-groups, such as African-American summary execution in the field by the Conferderate Army during the Civil War. Small-scale atrocities may represent anything from disrespect, regional propaganda or both.
In modern settings not involving ethnic conflict, atrocities on individual leaders are rare, partially because they tend backfire or simply escalate, as in the case of Breaker Morant. In ethnic conflict, atrocity is often just an expression of pure revenge, with no notion of justice involved. Lincoln considered responding with executions in-kind for every Black Union solider murdered on the field, but he recognized that the problem was a difference in point of view between the two sides that would lead to a spiraling of escalation in the inevitable tit-for-tat that would follow. Again, the problem was that the North considered the black man fully human and the South did not. From a strict Constitutional constructionist point of view, the South was correct in that the black man only counted for three-fifths a full human being, and that dehumanizing factor is what allowed for what others considered to be atrocity. Recall that the whole three-fifths notion was simply the result of compromise hammered out a hundred years earlier to bring the South into the Union in the first place.
See also
- Collateral damage
- Genocide
- Great Purge
- Holocaust
- List of massacres
- Mass deaths and atrocities of the twentieth century
- Murder
- My Lai Massacre
- Native American massacres
- Armenian Genocide
- Rwandan Genocide
- September 11, 2001 attacks
- Serial killing
- Terrorist incidents
- Torture
- Unit 731
Disambiguation
For the german metal band, see Atrocity.
For the album by the US rapper 50 Cent, see The Massacre.
Category:International criminal law
Category:Crimes
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