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重量

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{{hatnote|本条目介绍的是一个物理概念。口语上,「重量」也可能指「[[质量]]」。}}
{{Infobox physical quantity
| name = 重量
| width =
| image = [[File:Weeghaak.JPG|x200px]]
| caption = 用来测量物体重量的[[弹簧秤]]。
| unit = [[牛顿 (单位)|牛顿]](N)
| otherunits = [[磅力]] (lbf)
| symbols = <math>W</math>
| baseunits = kg⋅m⋅s<sup>−2</sup>
| dimension = <math>\mathsf{MLT}^{-2}</math>
| extensive = 是
| intensive = 否
| conserved = 否
| transformsas =
| derivations = {{plainlist|
* <math>W = mg</math>
* <math>W = ma</math>
}}
}}
在[[科学]]与[[工程学]]上,物体的'''重量'''指的通常是[[引力|重力]]作用在它身上的[[力]]。<ref name="Morrison"/><ref name="Galili"/>重量是[[向量]],它的量([[纯量]])一般用斜体 <math>W</math> 表示。重量是质量 <math>m</math> 和当地[[重力加速度]] <math>g</math> 的乘积<ref name="Gat"/>,即为:<math>W=mg</math>。重力的[[计量单位]]和[[力]]一样,也就是[[国际单位制]]({{lang|en|SI}})的「[[牛顿 (单位)|牛顿]]」。举例而言,一件质量为一公斤的物体在地球表面重9.8牛顿,而在[[月球]]上则重9.8牛顿的六分之一。根据这个定义,若要一个物体没有重量,原则上只有无限远离所有其他具有质量的物体才可能发生。虽然科学上重量和质量是不同的量,日常生活中常会将两者混用。例如转换或比较以[[磅力]]为单位的力和以公斤为单位的质量,反之亦然。<ref name="Canada"/>
== 历史 ==
[[File:3199 - Athens - Stoà of Attalus Museum - Bronze weights - Photo by Giovanni Dall'Orto, Nov 9 2009.jpg|thumb|公元前六世纪前后的[[古希腊]]官方青铜器(标示重量用),展示于雅典的[[阿塔罗斯柱廊|古代亚哥拉博物馆]]。]]
[[File:Weighing grain, from the Babur-namah.jpg|thumb|170px|秤穀类({{lang|en|Weighing Grain}})。来自{{tsl|en|Baburnama|巴布林回忆录}}。<ref name="Sur Das"/>]]
有关「轻」、「重」概念的讨论可以追溯至[[古希腊哲学|古希腊的哲学家]]。轻重曾被视为物体内在的性质。[[柏拉图]]将重量描述为物体寻找同类的自然倾向。对[[亚里士多德|亚里斯多德]]而言,轻重则代表恢复基本元素(空气、土、火、水)的自然秩序的倾向。他将「重」归因于土,而「轻」归因于火。[[阿基米德]]将重量视为与[[浮力]]相反的量,因为这两者决定了物体会浮起来或沉下去。而[[欧几里得]]给出了重量的第一个[[操作定义]]:重量是一物和他物相比的轻重,可用天秤测量。比起操作定义,用秤测量重量的历史自有文字记载就开始了。<ref name="Galili"/>
== 定义 ==
[[File:Nitrolympics TopFuel 2005.jpg|thumb|right|300px|这辆{{tsl|en|top fuel|火箭车}}能在0.86秒内从0加速到每小时160公里,水平加速度达5.3<math>g</math>。结合车辆静止时垂直向下的重力,由勾股定理可知,[[G力]]将达5.4<math>g</math>。若使用操作定义,G力将改变驾驶的重量;如果使用重力定义,驾驶的重量则不因车辆移动而改变。]]
「重量」有数种不同的定义,互相不见得等价。<ref name="Gat"/><ref name="King"/><ref name="French"/><ref name="Galili-Lehavi"/>
The operational definition, as usually given, does not explicitly exclude the effects of [[浮力|buoyancy]], which reduces the measured weight of an object when it is immersed in a fluid such as air or water. As a result, a floating [[气球|balloon]] or an object floating in water might be said to have zero weight.-->
=== ISO定义 ===
In the [[国际标准化组织|ISO]] International standard ISO 80000-4(2006),<ref name ="Quantities and units"/> describing the basic physical quantities and units in mechanics as a part of the International standard [[ISO/IEC 80000]], the definition of ''weight'' is given as:
{{quotation|
'''Definition'''
:<math>F_g = m g \, </math>,
:where ''m'' is mass and ''g'' is local acceleration of free fall.
'''Remarks'''
== 质量 ==
<!--这段来源也好少...-->
[[File:WeightNormal.svg|thumb|250px|An object with mass ''m'' resting on a surface and the corresponding [[隔离体图|free body diagram]] of just the object showing the [[力|force]]s acting on it. Notice that the amount of force that the table is pushing upward on the object (the N vector) is equal to the downward force of the object's weight (shown here as ''mg'', as weight is equal to the object's mass multiplied with the acceleration due to gravity): because these forces are equal, the object is in a state of [[力学平衡|equilibrium]] (all the forces and {{tsl|en|Moment (physics)||moments}} acting on it sum to zero).]]
{{Main|质量与重量的比较}}
In modern scientific usage, weight and [[质量|mass]] are fundamentally different quantities: mass is an {{tsl|en|Intrinsic and extrinsic properties||intrinsic}} property of [[物质|matter]], whereas weight is a ''force'' that results from the action of [[引力|gravity]] on matter: it measures how strongly the force of gravity pulls on that matter. However, in most practical everyday situations the word "weight" is used when, strictly, "mass" is meant.<ref name="Canada"/><ref name="NIST811wt"/> For example, most people would say that an object "weighs one kilogram", even though the kilogram is a unit of mass.
| pages=3480–3485
}}</ref>
 
<ref name ="Common">{{cite web
| url = https://www.nist.gov/pml/weights-and-measures/approximate-conversions-us-customary-measures-metric
| title = Common Conversion Factors, Approximate Conversions from U.S. Customary Measures to Metric
| publisher = [[国家标准技术研究所|National Institute of Standards and Technology]]
| accessdate = 2018-01-30
| archiveurl = https://web.archive.org/web/20180130125028/https://www.nist.gov/pml/weights-and-measures/approximate-conversions-us-customary-measures-metric
| archivedate = 2018-01-30
| deadurl = no
}}</ref>
 
}}
 
{{Classical mechanics derived SI units}}
 
[[Category:质量]]
[[Category:力]]
[[Category:生理学]]
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