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重量
,创建页面，内容为“{{translating|en:Weight||tpercent=30|time=2018-02-07}} {{noteTA |G1 = Physics }} {{hatnote|本条目介绍的是一个物理概念。口语上，「重量」也…”
{{translating|[[:en:Weight]]||tpercent=30|time=2018-02-07}}
{{noteTA
|G1 = Physics
}}
{{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"/>
[[经典力学|牛顿物理学]]和工程学也有个传统：视一物体的重量为其秤起来的重量。这裡的重量是施在一物上的反作用力。一般而言，测量物体的重量时，物体会被放置在相对于地球处于静止状态的秤上，而这个定义也能延伸到其他的运动状态。因此，自由落体的物体重量为零。这第二种重量的定义，允许地面上的物体处于失重状态。若忽略[[阻力|空气阻力]]，[[艾萨克·牛顿|艾萨克牛顿]]那颗著名的苹果从树上掉下来接触地面之前是没有重量的。
另外，根据[[相对论]]，重力是[[时空]][[曲率|弯曲]]的结果。教学界已经为「如何向学生定义重量」争论超过半世纪。目前的情况是多种概念并存，视情况使用不同概念。<ref name="Galili"/>
== 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"/>
根据亚里斯多德，重量是物体坠落的直接原因，其坠落速率应与重量成正比。后来，中世纪学者发现物体坠落的速率随时间增加。为了维持这种因果关系，重量的概念被修改，分成两部分：静止的重量（{{lang|en|still weight}}）和因重力导致的重量（{{lang|en|actual gravity}}）。前者为物体的本质，后者反应了坠落速率增加的原因。「重力导致的重量」这概念之后被[[让·布里丹]]的「[[冲力说|衝力]]」取代。其中衝力为[[动量]]的前身。<ref name="Galili"/>
{{tsl|en|Copernican heliocentrism|哥白尼的日心说|哥白尼世界观}}的兴起重振了「同类相吸」的想法（柏拉图），以解释天体间的互相吸引。17世纪，[[伽利略·伽利莱|伽利略]]在重量的观念上取得重大进展。他提出一种测量方法，来衡量运动中的物体和静止物体的重量差异。最终，他认爲物体的重量与物质的量成正比，而非速率（亚里斯多德）。<ref name="Galili"/>
=== 牛顿 ===
牛顿[[牛顿运动定律|运动定律]]和[[牛顿万有引力定律|万有引力定律]]的引入，进一步发展了重量的概念。重量和[[质量]]（物质的量）被区分开来。质量被认为是物体的基本性质，与其[[惯性]]相关；而重量则是重力作用于物体的结果，与物体的情况有关。特别的是，牛顿认为重量是相对的，是一对物体间的性质。例如，他曾写道：「行星们『对太阳的重量』必须是它们物质的量」{{noteTag|1=原文："{{lang|en|the weights of the planets ''towards the sun'' must be as their quantities of matter}}"}}。牛顿对重量的操作定义为：它与阻碍物体下降的力相反、值相等。<ref name="Galili"/>
牛顿认为时间和空间是[[绝对时空|绝对的]]，这让他有「真实的」（{{lang|en|ture}}，对应于 {{lang|en|relative}}，「相对的」）位置或真实的速度这类的概念。他也知道秤量的重量会受浮力等环境因素影响，因此引入了「视重」（{{lang|en|apparent weight}}）这个词来表达因不完善测量条件造成的假重量，以区隔由重力定义的「真实重量」。这裡的视重和现代的不太一样，现代的视重通常与惯性力有关，例如用来解释地理上[[纬度]]和离心力的关系。<ref name="Galili"/>
<!--暂时懒找来源
Although Newtonian physics made a clear distinction between weight and mass, the term weight continued to be commonly used when people meant mass. This led the 3rd [[国际度量衡大会|General Conference on Weights and Measures]] (CGPM) of 1901 to officially declare "The word ''weight'' denotes a quantity of the same nature as a ''force'': the weight of a body is the product of its mass and the acceleration due to gravity", thus distinguishing it from mass for official usage.
-->
=== 相对论 ===
20世纪，牛顿的绝对时空观受到[[相对论]]的挑战。爱因斯坦的[[等效原理]]认为不同参考系的观察者是平等的，这会使得观察者无法区分自己是处在加速中的参考系或是重力场之中，进而促使「[[重力]]」的概念与「重量」分离。至此，重量这个概念在科学上的历史可视为终结了。不过在日常生活和物理教学上，重量的概念依然有用。相对论的引入，使教学界自1960年代以来对「如何向学生定义重量」进行了相当多辩论。教师们可以选择使用「因重力引起的力」（名义定义）或是「秤重」这个行为（操作定义）来定义重量。<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"/>
=== 重力定义 ===
重量最常见的定义为「重力作用在物体上的力」，可在入门等级的物理教科书中找到。<ref name="Morrison"/><ref name="Galili-Lehavi"/>公式通常可表达为<math>W = mg</math>，其中<math>W</math>为重量，<math>m</math>为物体质量，<math>g</math>为[[重力加速度]]。
1901年，第三届[[国际度量衡大会]]（CGPM）确立了他们正式的重量定义：
{{quotation|"The word ''weight'' denotes a quantity of the same nature{{noteTag|1=The phrase "quantity of the same nature" is a literal translation of the [[法语|French]] phrase ''grandeur de la même nature''. Although this is an authorized translation, VIM 3 of the [[国际度量衡局|International Bureau of Weights and Measures]] recommends translating ''grandeurs de même nature'' as ''quantities of the same kind''.<ref name = "JCGM/WG 2"/>}} as a ''force'': the weight of a body is the product of its mass and the acceleration due to gravity."
|Resolution 2 of the 3rd General Conference on Weights and Measures<ref name="3rdCGPM"/><ref name=taylor/>}}
这项决议将重量定义为向量（由于力是向量）。然而，一些教科书使用了下列定义，将重量当成纯量：
{{quotation|"The weight ''W'' of a body is equal to the magnitude ''F<sub>g</sub>'' of the gravitational force on the body."<ref name="Halliday 2007 95"/>}}
不同地点的重力加速度不一样。有时会直接使用[[标准重力]]提供的标准值<math>9.80665 m/s^2</math>。<ref name="3rdCGPM"/>
量值等于<math>mg</math>牛顿的力也会写为 {{lang|en|kg-wt}}（{{lang|en|m kilogram weight}} 的缩写）。<ref name ="Chester"/>
{{multiple image
| align = right
| direction = horizontal
| header = Measuring weight versus mass
| image1 = Weegschaal-1.jpg
| width1 = 125
| image2 = Bascula_9.jpg
| width2 = 220
| footer = Left: A [[计重秤|spring scale]] measures weight, by seeing how much the object pushes on a spring (inside the device). On the Moon, an object would give a lower reading. Right: A [[计重秤|balance scale]] indirectly measures mass,<!-- It compares weights. It has the secondary effect of comparing masses because weight is proportional to mass. --> by comparing an object to references. On the Moon, an object would give the same reading, because the object and references would ''both'' become lighter.}}
=== 操作定义 ===
重量的操作定义为「秤重」物体得到的重量，也就是「支撑物体的[[力]]」。<ref name="King"/>
<!--以下无来源，有些甚至可能原创研究-->
<!--Since, W=downward force on the body by the centre of earth, and there is no acceleration in the body. So, there exists opposite and equal force by the support on the body. Also it is equal to the force exerted by the body on its support because action and reaction have same numerical value and opposite direction.
This can make a considerable difference, depending on the details; for example, an object in [[自由落体|free fall]] exerts little if any force on its support, a situation that is commonly referred to as [[失重|weightlessness]]. However, being in free fall does not affect the weight according to the gravitational definition. Therefore, the operational definition is sometimes refined by requiring that the object be at rest.{{Citation needed|date=May 2010}} However, this raises the issue of defining "at rest" (usually being at rest with respect to the Earth is implied by using [[标准重力|standard gravity]]{{Citation needed|date=May 2010}}). In the operational definition, the weight of an object at rest on the surface of the Earth is lessened by the effect of the centrifugal force from the Earth's rotation.
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'''
*When the reference frame is Earth, this quantity comprises not only the local gravitational force, but also the local centrifugal force due to the rotation of the Earth, a force which varies with latitude.
*The effect of atmospheric buoyancy is excluded in the weight.
*In common parlance, the name "weight" continues to be used where "mass" is meant, but this practice is deprecated.
|ISO 80000-4 (2006)}}
The definition is dependent on the chosen [[参考系|frame of reference]]. When the chosen frame is co-moving with the object in question then this definition precisely agrees with the operational definition.<ref name="French"/> If the specified frame is the surface of the Earth, the weight according to the ISO and gravitational definitions differ only by the centrifugal effects due to the rotation of the Earth.
=== 视重 ===
{{See also2|{{tsl|en|Apparent weight|视重}}}}
In many real world situations the act of weighing may produce a result that differs from the ideal value provided by the definition used. This is usually referred to as the apparent weight of the object. A common example of this is the effect of [[浮力|buoyancy]], when an object is immersed in a [[流体|fluid]] the displacement of the fluid will cause an upward force on the object, making it appear lighter when weighed on a scale.<ref name = "Bell, F."/> The apparent weight may be similarly affected by {{tsl|en|levitation||levitation}} and mechanical suspension. When the gravitational definition of weight is used, the operational weight measured by an accelerating scale is often also referred to as the apparent weight.<ref name = "Galili, Igal"/>
== 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.
The distinction between mass and weight is unimportant for many practical purposes because the strength of gravity does not vary too much on the surface of the Earth. In a uniform gravitational field, the gravitational force exerted on an object (its weight) is [[比例|directly proportional]] to its mass. For example, object A weighs 10 times as much as object B, so therefore the mass of object A is 10 times greater than that of object B. This means that an object's mass can be measured indirectly by its weight, and so, for everyday purposes, [[重量|weighing]] (using a [[计重秤|weighing scale]]) is an entirely acceptable way of measuring mass. Similarly, a [[计重秤|balance]] measures mass indirectly by comparing the weight of the measured item to that of an object(s) of known mass. Since the measured item and the comparison mass are in virtually the same location, so experiencing the same [[引力|gravitational field]], the effect of varying gravity does not affect the comparison or the resulting measurement.
The Earth's [[引力|gravitational field]] is not uniform but can vary by as much as 0.5%<ref name = "Hodgeman"/> at different locations on Earth (see [[地球引力|Earth's gravity]]). These variations alter the relationship between weight and mass, and must be taken into account in high precision weight measurements that are intended to indirectly measure mass. [[弹簧秤|Spring scale]]s, which measure local weight, must be calibrated at the location at which the objects will be used to show this standard weight, to be legal for commerce.{{Citation needed|date=May 2010|reason=Doesn't this depend on the jurisdiction?}}
This table shows the variation of acceleration due to gravity (and hence the variation of weight) at various locations on the Earth's surface.<ref>{{cite book
|first = John B
|last = Clark
|title = Physical and Mathematical Tables
|publisher = Oliver and Boyd
|date = 1964}}</ref>
{| class="wikitable" border="2"
|-
! 地点
! 纬度
! m/s<sup>2</sup>
|-
| [[赤道]]
| 0°
| 9.7803
|-
| [[悉尼]]
| 33°52′ S
| 9.7968
|-
| [[阿伯丁]]
| 57°9′ N
| 9.8168
|-
|-
| [[北极点]]
| 90° N
| 9.8322
|-
|}
The historic use of "weight" for "mass" also persists in some scientific terminology – for example, the [[化学|chemical]] terms "atomic weight", "molecular weight", and "formula weight", can still be found rather than the preferred "[[原子量|atomic mass]]" etc.
In a different gravitational field, for example, on the surface of the [[月球|Moon]], an object can have a significantly different weight than on Earth. The gravity on the surface of the Moon is only about one-sixth as strong as on the surface of the Earth. A one-kilogram mass is still a one-kilogram mass (as mass is an extrinsic property of the object) but the downward force due to gravity, and therefore its weight, is only one-sixth of what the object would have on Earth. So a man of mass 180 [[磅|pounds]] weighs only about 30 [[磅力|pounds-force]] when visiting the Moon.
=== SI制单位 ===
In most modern scientific work, physical quantities are measured in [[国际单位制|SI]] units. The SI unit of weight is the same as that of force: the [[牛顿 (单位)|newton]] (N) – a derived unit which can also be expressed in [[国际单位制基本单位|SI base unit]]s as kg·m/s<sup>2</sup> (kilograms times meters per second squared).<ref name=NIST811wt/>
In commercial and everyday use, the term "weight" is usually used to mean mass, and the verb "to weigh" means "to determine the mass of" or "to have a mass of". Used in this sense, the proper SI unit is the [[千克|kilogram]] (kg).<ref name=NIST811wt/>
=== 其他单位 ===
In [[美制单位|United States customary units]], the pound can be either a unit of force or a unit of mass.<ref name ="Common"/> Related units used in some distinct, separate subsystems of units include the {{tsl|en|poundal||poundal}} and the [[斯勒格|slug]]. The poundal is defined as the force necessary to accelerate an object of one-pound ''mass'' at 1 ft/s<sup>2</sup>, and is equivalent to about 1/32.2 of a pound-''force''. The slug is defined as the amount of mass that accelerates at 1 ft/s<sup>2</sup> when one pound-force is exerted on it, and is equivalent to about 32.2 pounds (mass).
The [[千克力|kilogram-force]] is a non-SI unit of force, defined as the force exerted by a one kilogram mass in standard Earth gravity (equal to 9.80665 newtons exactly). The [[达因|dyne]] is the [[厘米-克-秒制|cgs]] unit of force and is not a part of SI, while weights measured in the cgs unit of mass, the gram, remain a part of SI.
<!--以下完全没来源-->
<!--
== 感知 ==
{{See also2|{{tsl|en|Apparent weight|视重}}}}
The sensation of weight is caused by the force exerted by fluids in the [[前庭系统|vestibular system]], a three-dimensional set of tubes in the inner [[耳|ear]].{{Dubious|Sensation of Weight|date=June 2010}} It is actually the sensation of [[G力|g-force]], regardless of whether this is due to being stationary in the presence of gravity, or, if the person is in motion, the result of any other forces acting on the body such as in the case of acceleration or deceleration of a lift, or centrifugal forces when turning sharply.
== 量测 ==
{{Main article|计重秤}}
[[File:Peso-Valdivia-dsc02545.jpg|thumb|给卡车秤重的{{tsl|en|weighbridge|地磅}}。]]
Weight is commonly measured using one of two methods. A [[计重秤|spring scale]] or [[计重秤|hydraulic or pneumatic scale]] measures local weight, the local [[力|force]] of [[引力|gravity]] on the object (strictly {{tsl|en|apparent weight||''apparent'' weight force}}). Since the local force of gravity can vary by up to 0.5% at different locations, spring scales will measure slightly different weights for the same object (the same mass) at different locations. To standardize weights, scales are always calibrated to read the weight an object would have at a nominal [[标准重力|standard gravity]] of 9.80665 m/s<sup>2</sup> (approx. 32.174 ft/s<sup>2</sup>). However, this calibration is done at the factory. When the scale is moved to another location on Earth, the force of gravity will be different, causing a slight error. So to be highly accurate, and legal for commerce, [[弹簧秤|spring scale]]s must be re-calibrated at the location at which they will be used.
A ''[[计重秤|balance]]'' on the other hand, compares the weight of an unknown object in one scale pan to the weight of standard masses in the other, using a [[杠杆|lever]] mechanism – a lever-balance. The standard masses are often referred to, non-technically, as ''"weights"''. Since any variations in gravity will act equally on the unknown and the known weights, a lever-balance will indicate the same value at any location on Earth. Therefore, balance ''"weights"'' are usually calibrated and marked in [[质量|mass]] units, so the lever-balance measures mass by comparing the Earth's attraction on the unknown object and standard masses in the scale pans. In the absence of a gravitational field, away from planetary bodies (e.g. space), a lever-balance would not work, but on the Moon, for example, it would give the same reading as on Earth. Some balances can be marked in weight units, but since the weights are calibrated at the factory for standard gravity, the balance will measure standard weight, i.e. what the object would weigh at standard gravity, not the actual local force of gravity on the object.
If the actual force of gravity on the object is needed, this can be calculated by multiplying the mass measured by the balance by the acceleration due to gravity – either standard gravity (for everyday work) or the precise local gravity (for precision work). Tables of the gravitational acceleration at different locations can be found on the web.
'''Gross weight''' is a term that is generally found in commerce or trade applications, and refers to the total weight of a product and its packaging. Conversely, '''net weight''' refers to the weight of the product alone, discounting the weight of its container or packaging; and '''{{tsl|en|tare weight||tare weight}}''' is the weight of the packaging alone.
== 不同天体上的相对重量 ==
{{Main article|地球引力|表面重力}}
The table below shows comparative [[表面重力|gravitational accelerations at the surface]] of the Sun, the Earth's moon, each of the planets in the solar system. The “surface” is taken to mean the cloud tops of the [[气态巨行星|gas giants]] (Jupiter, Saturn, Uranus and Neptune). For the Sun, the surface is taken to mean the [[光球|photosphere]]. The values in the table have not been de-rated for the centrifugal effect of planet rotation (and cloud-top wind speeds for the gas giants) and therefore, generally speaking, are similar to the actual gravity that would be experienced near the poles.
{| class="wikitable" border="1"
|-
! 天体
! 地球重力<br>的倍数
! [[表面重力]]<br>m/s<sup>2</sup>
|-
| [[太阳]]
| 27.90
| 274.1
|-
| [[水星]]
| 0.3770
| 3.703
|-
| [[金星]]
| 0.9032
| 8.872
|-
| [[地球]]
| 1 （定义）
| 9.8226{{noteTag|1=这个值排除了地球自转导致的离心力的影响，因此大于9.806 65 <math>m/s^2</math>（[[标准重力]]）}}
|-
| [[月球]]
| 0.1655
| 1.625
|-
| [[火星]]
| 0.3895
| 3.728
|-
| [[木星]]
| 2.640
| 25.93
|-
| [[土星]]
| 1.139
| 11.19
|-
| [[天王星]]
| 0.917
| 9.01
|-
| [[海王星]]
| 1.148
| 11.28
|-
|}
-->
== 延伸阅读 ==
* [[体重]]
== 注释 ==
{{noteFoot}}
== 参考资料 ==
{{reflist|2|refs=
<ref name="Morrison">{{cite journal
|title=Weight and gravity - the need for consistent definitions
|author=Richard C. Morrison
|journal={{tsl|en|The Physics Teacher||The Physics Teacher}}
|volume=37 |page=51 |date=1999 |doi=10.1119/1.880152
|bibcode = 1999PhTea..37...51M }}</ref>
<ref name="Galili">{{cite journal
|title=Weight versus gravitational force: historical and educational perspectives
|author=Igal Galili
|journal=International Journal of Science Education
|volume=23 |page=1073 |date=2001 |doi=10.1080/09500690110038585
|bibcode = 2001IJSEd..23.1073G }}</ref>
<ref name="Gat">{{cite book |title=Standardization of Technical Terminology: Principles and Practice – ''second volume'' |editor=Richard Alan Strehlow |date=1988 |publisher=[[美国材料和试验协会|ASTM International]] |isbn=978-0-8031-1183-7 |chapter=The weight of mass and the mess of weight |last=Gat |first=Uri |pages=45–48 |url=https://books.google.com/books?id=CoB5w9Km0mUC&pg=PA45}}</ref>
<ref name="Canada">The National Standard of Canada, CAN/CSA-Z234.1-89 Canadian Metric Practice Guide, January 1989:
*'''5.7.3''' Considerable confusion exists in the use of the term "weight." In commercial and everyday use, the term "weight" nearly always means mass. In science and technology "weight" has primarily meant a force due to gravity. In scientific and technical work, the term "weight" should be replaced by the term "mass" or "force," depending on the application.
*'''5.7.4''' The use of the verb "to weigh" meaning "to determine the mass of," e.g., "I weighed this object and determined its mass to be 5 kg," is correct.</ref>
<ref name="Sur Das">{{cite web|author=Sur Das |url=http://warfare.atspace.eu/Moghul/Baburnama/Weighing_Grain.htm |title=Weighing Grain |date=1590s |work=Baburnama |archiveurl = http://archive.fo/hYPTy |archivedate = 2013-07-14 |deadurl = yes}}</ref>
<ref name="King">{{cite journal
|title=Weight and weightlessness
|author=Allen L. King
|journal={{tsl|en|American Journal of Physics||American Journal of Physics}} |volume=30 |page=387 |date=1963 |doi=10.1119/1.1942032
|bibcode = 1962AmJPh..30..387K }}</ref>
<ref name="French">{{cite journal |title=On weightlessness |author=A. P. French |journal={{tsl|en|American Journal of Physics||American Journal of Physics}} |volume=63 |pages=105–106 |date=1995 |doi=10.1119/1.17990|bibcode = 1995AmJPh..63..105F }}</ref>
<ref name="Galili-Lehavi">{{cite journal |last1=Galili |first1=I. |last2=Lehavi |first2=Y. |date=2003 |title=The importance of weightlessness and tides in teaching gravitation |journal={{tsl|en|American Journal of Physics||American Journal of Physics}} |volume=71 |issue=11 |pages=1127–1135 |url=http://sites.huji.ac.il/science/stc/staff_h/Igal/Research%20Articles/Weight-AJP.pdf |doi=10.1119/1.1607336|bibcode = 2003AmJPh..71.1127G }}</ref>
<ref name = "JCGM/WG 2">{{cite book
|author=Working Group 2 of the Joint Committee for Guides in Metrology (JCGM/WG 2)
|title=International vocabulary of metrology — Basic and general concepts and associated terms (VIM) — Vocabulaire international de métrologie — Concepts fondamentaux et généraux et termes associés (VIM)
|url=http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2008.pdf
|date=2008 |edition=3rd |type=JCGM 200:2008 |publisher=[[国际度量衡局|BIPM]]
|at=Note 3 to Section 1.2
|language=English, French
|archiveurl = https://web.archive.org/web/20180127200534/https://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2008.pdf
|archivedate = 2018-01-27
|deadurl = no
}}</ref>
<ref name=taylor>{{cite book |editor=Barry N. Taylor |editor2=Ambler Thompson |title=The International System of Units (SI) |publisher=[[国家标准技术研究所|NIST]] |date=2008 |series=NIST Special Publication 330 |edition=2008 |page=52 |url=http://physics.nist.gov/Pubs/SP330/sp330.pdf |archiveurl = https://web.archive.org/web/20170622033951/http://physics.nist.gov/Pubs/SP330/sp330.pdf |archivedate = 2017-06-22 |deadurl =yes}}</ref>
<ref name="Halliday 2007 95">{{cite book |title=Fundamentals of Physics |volume=1 |first=David |last=Halliday |first2=Robert |last2=Resnick |first3=Jearl |last3=Walker |publisher= Wiley |date=2007 |edition=8th |page=95 |isbn= 978-0-470-04473-5}}</ref>
<ref name="3rdCGPM">{{cite web
|url=http://www.bipm.org/en/CGPM/db/3/2/
|title=Resolution of the 3rd meeting of the CGPM (1901)
|publisher=BIPM
|archiveurl = https://web.archive.org/web/20180117131214/https://www.bipm.org/en/CGPM/db/3/2/
|archivedate = 2018-01-17
|deadurl = no
}}</ref>
<ref name ="Chester">{{cite book |title = Mechanics |author1 = Chester, W. |publisher = George Allen & Unwin. |location = London |date = 1979 |ISBN = 0-04-510059-4 |page = 83}}</ref>
<ref name ="Quantities and units">ISO 80000-4:2006, Quantities and units - Part 4: Mechanics</ref>
<ref name = "Bell, F.">{{cite book
|title=Principles of mechanics and biomechanics
|author=Bell, F.
|isbn=978-0-7487-3332-3
|url=https://books.google.com/books?id=bPcPnZQ36KwC&pg=PA174
|pages=174–176
|date=1998
|publisher=Stanley Thornes Ltd
}}</ref>
<ref name = "Galili, Igal">{{cite journal
|author = Galili, Igal
|title = Weight and gravity: teachers’ ambiguity and students’ confusion about the concepts
|journal = International Journal of Science Education
|volume = 15
|number = 2
|pages = 149–162
|date = 1993
|doi = 10.1080/0950069930150204
|bibcode = 1993IJSEd..15..149G }}</ref>
<ref name="NIST811wt">{{cite web |author=A. Thompson |author2=B. N. Taylor |last-author-amp=yes |title=The NIST Guide for the use of the International System of Units, Section 8: Comments on Some Quantities and Their Units |work=Special Publication 811 |url=http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=200349 |publisher=[[国家标准技术研究所|NIST]] |origyear = 2009-07-02 |date = 2010-03-03 |accessdate=2010-05-22|archiveurl = https://web.archive.org/web/20180130125355/http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=200349 |archivedate = 2018-01-30 |deadurl = no}}</ref>
<ref name = "Hodgeman">{{cite book
| editor-last = Hodgeman
| editor-first = Charles
| title = Handbook of Chemistry and Physics
| edition = 44th
| publisher = Chemical Rubber Publishing Co.
| date = 1961
| location = Cleveland, USA
| 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]]
{{noteTA
|G1 = Physics
}}
{{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"/>
[[经典力学|牛顿物理学]]和工程学也有个传统：视一物体的重量为其秤起来的重量。这裡的重量是施在一物上的反作用力。一般而言，测量物体的重量时，物体会被放置在相对于地球处于静止状态的秤上，而这个定义也能延伸到其他的运动状态。因此，自由落体的物体重量为零。这第二种重量的定义，允许地面上的物体处于失重状态。若忽略[[阻力|空气阻力]]，[[艾萨克·牛顿|艾萨克牛顿]]那颗著名的苹果从树上掉下来接触地面之前是没有重量的。
另外，根据[[相对论]]，重力是[[时空]][[曲率|弯曲]]的结果。教学界已经为「如何向学生定义重量」争论超过半世纪。目前的情况是多种概念并存，视情况使用不同概念。<ref name="Galili"/>
== 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"/>
根据亚里斯多德，重量是物体坠落的直接原因，其坠落速率应与重量成正比。后来，中世纪学者发现物体坠落的速率随时间增加。为了维持这种因果关系，重量的概念被修改，分成两部分：静止的重量（{{lang|en|still weight}}）和因重力导致的重量（{{lang|en|actual gravity}}）。前者为物体的本质，后者反应了坠落速率增加的原因。「重力导致的重量」这概念之后被[[让·布里丹]]的「[[冲力说|衝力]]」取代。其中衝力为[[动量]]的前身。<ref name="Galili"/>
{{tsl|en|Copernican heliocentrism|哥白尼的日心说|哥白尼世界观}}的兴起重振了「同类相吸」的想法（柏拉图），以解释天体间的互相吸引。17世纪，[[伽利略·伽利莱|伽利略]]在重量的观念上取得重大进展。他提出一种测量方法，来衡量运动中的物体和静止物体的重量差异。最终，他认爲物体的重量与物质的量成正比，而非速率（亚里斯多德）。<ref name="Galili"/>
=== 牛顿 ===
牛顿[[牛顿运动定律|运动定律]]和[[牛顿万有引力定律|万有引力定律]]的引入，进一步发展了重量的概念。重量和[[质量]]（物质的量）被区分开来。质量被认为是物体的基本性质，与其[[惯性]]相关；而重量则是重力作用于物体的结果，与物体的情况有关。特别的是，牛顿认为重量是相对的，是一对物体间的性质。例如，他曾写道：「行星们『对太阳的重量』必须是它们物质的量」{{noteTag|1=原文："{{lang|en|the weights of the planets ''towards the sun'' must be as their quantities of matter}}"}}。牛顿对重量的操作定义为：它与阻碍物体下降的力相反、值相等。<ref name="Galili"/>
牛顿认为时间和空间是[[绝对时空|绝对的]]，这让他有「真实的」（{{lang|en|ture}}，对应于 {{lang|en|relative}}，「相对的」）位置或真实的速度这类的概念。他也知道秤量的重量会受浮力等环境因素影响，因此引入了「视重」（{{lang|en|apparent weight}}）这个词来表达因不完善测量条件造成的假重量，以区隔由重力定义的「真实重量」。这裡的视重和现代的不太一样，现代的视重通常与惯性力有关，例如用来解释地理上[[纬度]]和离心力的关系。<ref name="Galili"/>
<!--暂时懒找来源
Although Newtonian physics made a clear distinction between weight and mass, the term weight continued to be commonly used when people meant mass. This led the 3rd [[国际度量衡大会|General Conference on Weights and Measures]] (CGPM) of 1901 to officially declare "The word ''weight'' denotes a quantity of the same nature as a ''force'': the weight of a body is the product of its mass and the acceleration due to gravity", thus distinguishing it from mass for official usage.
-->
=== 相对论 ===
20世纪，牛顿的绝对时空观受到[[相对论]]的挑战。爱因斯坦的[[等效原理]]认为不同参考系的观察者是平等的，这会使得观察者无法区分自己是处在加速中的参考系或是重力场之中，进而促使「[[重力]]」的概念与「重量」分离。至此，重量这个概念在科学上的历史可视为终结了。不过在日常生活和物理教学上，重量的概念依然有用。相对论的引入，使教学界自1960年代以来对「如何向学生定义重量」进行了相当多辩论。教师们可以选择使用「因重力引起的力」（名义定义）或是「秤重」这个行为（操作定义）来定义重量。<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"/>
=== 重力定义 ===
重量最常见的定义为「重力作用在物体上的力」，可在入门等级的物理教科书中找到。<ref name="Morrison"/><ref name="Galili-Lehavi"/>公式通常可表达为<math>W = mg</math>，其中<math>W</math>为重量，<math>m</math>为物体质量，<math>g</math>为[[重力加速度]]。
1901年，第三届[[国际度量衡大会]]（CGPM）确立了他们正式的重量定义：
{{quotation|"The word ''weight'' denotes a quantity of the same nature{{noteTag|1=The phrase "quantity of the same nature" is a literal translation of the [[法语|French]] phrase ''grandeur de la même nature''. Although this is an authorized translation, VIM 3 of the [[国际度量衡局|International Bureau of Weights and Measures]] recommends translating ''grandeurs de même nature'' as ''quantities of the same kind''.<ref name = "JCGM/WG 2"/>}} as a ''force'': the weight of a body is the product of its mass and the acceleration due to gravity."
|Resolution 2 of the 3rd General Conference on Weights and Measures<ref name="3rdCGPM"/><ref name=taylor/>}}
这项决议将重量定义为向量（由于力是向量）。然而，一些教科书使用了下列定义，将重量当成纯量：
{{quotation|"The weight ''W'' of a body is equal to the magnitude ''F<sub>g</sub>'' of the gravitational force on the body."<ref name="Halliday 2007 95"/>}}
不同地点的重力加速度不一样。有时会直接使用[[标准重力]]提供的标准值<math>9.80665 m/s^2</math>。<ref name="3rdCGPM"/>
量值等于<math>mg</math>牛顿的力也会写为 {{lang|en|kg-wt}}（{{lang|en|m kilogram weight}} 的缩写）。<ref name ="Chester"/>
{{multiple image
| align = right
| direction = horizontal
| header = Measuring weight versus mass
| image1 = Weegschaal-1.jpg
| width1 = 125
| image2 = Bascula_9.jpg
| width2 = 220
| footer = Left: A [[计重秤|spring scale]] measures weight, by seeing how much the object pushes on a spring (inside the device). On the Moon, an object would give a lower reading. Right: A [[计重秤|balance scale]] indirectly measures mass,<!-- It compares weights. It has the secondary effect of comparing masses because weight is proportional to mass. --> by comparing an object to references. On the Moon, an object would give the same reading, because the object and references would ''both'' become lighter.}}
=== 操作定义 ===
重量的操作定义为「秤重」物体得到的重量，也就是「支撑物体的[[力]]」。<ref name="King"/>
<!--以下无来源，有些甚至可能原创研究-->
<!--Since, W=downward force on the body by the centre of earth, and there is no acceleration in the body. So, there exists opposite and equal force by the support on the body. Also it is equal to the force exerted by the body on its support because action and reaction have same numerical value and opposite direction.
This can make a considerable difference, depending on the details; for example, an object in [[自由落体|free fall]] exerts little if any force on its support, a situation that is commonly referred to as [[失重|weightlessness]]. However, being in free fall does not affect the weight according to the gravitational definition. Therefore, the operational definition is sometimes refined by requiring that the object be at rest.{{Citation needed|date=May 2010}} However, this raises the issue of defining "at rest" (usually being at rest with respect to the Earth is implied by using [[标准重力|standard gravity]]{{Citation needed|date=May 2010}}). In the operational definition, the weight of an object at rest on the surface of the Earth is lessened by the effect of the centrifugal force from the Earth's rotation.
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'''
*When the reference frame is Earth, this quantity comprises not only the local gravitational force, but also the local centrifugal force due to the rotation of the Earth, a force which varies with latitude.
*The effect of atmospheric buoyancy is excluded in the weight.
*In common parlance, the name "weight" continues to be used where "mass" is meant, but this practice is deprecated.
|ISO 80000-4 (2006)}}
The definition is dependent on the chosen [[参考系|frame of reference]]. When the chosen frame is co-moving with the object in question then this definition precisely agrees with the operational definition.<ref name="French"/> If the specified frame is the surface of the Earth, the weight according to the ISO and gravitational definitions differ only by the centrifugal effects due to the rotation of the Earth.
=== 视重 ===
{{See also2|{{tsl|en|Apparent weight|视重}}}}
In many real world situations the act of weighing may produce a result that differs from the ideal value provided by the definition used. This is usually referred to as the apparent weight of the object. A common example of this is the effect of [[浮力|buoyancy]], when an object is immersed in a [[流体|fluid]] the displacement of the fluid will cause an upward force on the object, making it appear lighter when weighed on a scale.<ref name = "Bell, F."/> The apparent weight may be similarly affected by {{tsl|en|levitation||levitation}} and mechanical suspension. When the gravitational definition of weight is used, the operational weight measured by an accelerating scale is often also referred to as the apparent weight.<ref name = "Galili, Igal"/>
== 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.
The distinction between mass and weight is unimportant for many practical purposes because the strength of gravity does not vary too much on the surface of the Earth. In a uniform gravitational field, the gravitational force exerted on an object (its weight) is [[比例|directly proportional]] to its mass. For example, object A weighs 10 times as much as object B, so therefore the mass of object A is 10 times greater than that of object B. This means that an object's mass can be measured indirectly by its weight, and so, for everyday purposes, [[重量|weighing]] (using a [[计重秤|weighing scale]]) is an entirely acceptable way of measuring mass. Similarly, a [[计重秤|balance]] measures mass indirectly by comparing the weight of the measured item to that of an object(s) of known mass. Since the measured item and the comparison mass are in virtually the same location, so experiencing the same [[引力|gravitational field]], the effect of varying gravity does not affect the comparison or the resulting measurement.
The Earth's [[引力|gravitational field]] is not uniform but can vary by as much as 0.5%<ref name = "Hodgeman"/> at different locations on Earth (see [[地球引力|Earth's gravity]]). These variations alter the relationship between weight and mass, and must be taken into account in high precision weight measurements that are intended to indirectly measure mass. [[弹簧秤|Spring scale]]s, which measure local weight, must be calibrated at the location at which the objects will be used to show this standard weight, to be legal for commerce.{{Citation needed|date=May 2010|reason=Doesn't this depend on the jurisdiction?}}
This table shows the variation of acceleration due to gravity (and hence the variation of weight) at various locations on the Earth's surface.<ref>{{cite book
|first = John B
|last = Clark
|title = Physical and Mathematical Tables
|publisher = Oliver and Boyd
|date = 1964}}</ref>
{| class="wikitable" border="2"
|-
! 地点
! 纬度
! m/s<sup>2</sup>
|-
| [[赤道]]
| 0°
| 9.7803
|-
| [[悉尼]]
| 33°52′ S
| 9.7968
|-
| [[阿伯丁]]
| 57°9′ N
| 9.8168
|-
|-
| [[北极点]]
| 90° N
| 9.8322
|-
|}
The historic use of "weight" for "mass" also persists in some scientific terminology – for example, the [[化学|chemical]] terms "atomic weight", "molecular weight", and "formula weight", can still be found rather than the preferred "[[原子量|atomic mass]]" etc.
In a different gravitational field, for example, on the surface of the [[月球|Moon]], an object can have a significantly different weight than on Earth. The gravity on the surface of the Moon is only about one-sixth as strong as on the surface of the Earth. A one-kilogram mass is still a one-kilogram mass (as mass is an extrinsic property of the object) but the downward force due to gravity, and therefore its weight, is only one-sixth of what the object would have on Earth. So a man of mass 180 [[磅|pounds]] weighs only about 30 [[磅力|pounds-force]] when visiting the Moon.
=== SI制单位 ===
In most modern scientific work, physical quantities are measured in [[国际单位制|SI]] units. The SI unit of weight is the same as that of force: the [[牛顿 (单位)|newton]] (N) – a derived unit which can also be expressed in [[国际单位制基本单位|SI base unit]]s as kg·m/s<sup>2</sup> (kilograms times meters per second squared).<ref name=NIST811wt/>
In commercial and everyday use, the term "weight" is usually used to mean mass, and the verb "to weigh" means "to determine the mass of" or "to have a mass of". Used in this sense, the proper SI unit is the [[千克|kilogram]] (kg).<ref name=NIST811wt/>
=== 其他单位 ===
In [[美制单位|United States customary units]], the pound can be either a unit of force or a unit of mass.<ref name ="Common"/> Related units used in some distinct, separate subsystems of units include the {{tsl|en|poundal||poundal}} and the [[斯勒格|slug]]. The poundal is defined as the force necessary to accelerate an object of one-pound ''mass'' at 1 ft/s<sup>2</sup>, and is equivalent to about 1/32.2 of a pound-''force''. The slug is defined as the amount of mass that accelerates at 1 ft/s<sup>2</sup> when one pound-force is exerted on it, and is equivalent to about 32.2 pounds (mass).
The [[千克力|kilogram-force]] is a non-SI unit of force, defined as the force exerted by a one kilogram mass in standard Earth gravity (equal to 9.80665 newtons exactly). The [[达因|dyne]] is the [[厘米-克-秒制|cgs]] unit of force and is not a part of SI, while weights measured in the cgs unit of mass, the gram, remain a part of SI.
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== 感知 ==
{{See also2|{{tsl|en|Apparent weight|视重}}}}
The sensation of weight is caused by the force exerted by fluids in the [[前庭系统|vestibular system]], a three-dimensional set of tubes in the inner [[耳|ear]].{{Dubious|Sensation of Weight|date=June 2010}} It is actually the sensation of [[G力|g-force]], regardless of whether this is due to being stationary in the presence of gravity, or, if the person is in motion, the result of any other forces acting on the body such as in the case of acceleration or deceleration of a lift, or centrifugal forces when turning sharply.
== 量测 ==
{{Main article|计重秤}}
[[File:Peso-Valdivia-dsc02545.jpg|thumb|给卡车秤重的{{tsl|en|weighbridge|地磅}}。]]
Weight is commonly measured using one of two methods. A [[计重秤|spring scale]] or [[计重秤|hydraulic or pneumatic scale]] measures local weight, the local [[力|force]] of [[引力|gravity]] on the object (strictly {{tsl|en|apparent weight||''apparent'' weight force}}). Since the local force of gravity can vary by up to 0.5% at different locations, spring scales will measure slightly different weights for the same object (the same mass) at different locations. To standardize weights, scales are always calibrated to read the weight an object would have at a nominal [[标准重力|standard gravity]] of 9.80665 m/s<sup>2</sup> (approx. 32.174 ft/s<sup>2</sup>). However, this calibration is done at the factory. When the scale is moved to another location on Earth, the force of gravity will be different, causing a slight error. So to be highly accurate, and legal for commerce, [[弹簧秤|spring scale]]s must be re-calibrated at the location at which they will be used.
A ''[[计重秤|balance]]'' on the other hand, compares the weight of an unknown object in one scale pan to the weight of standard masses in the other, using a [[杠杆|lever]] mechanism – a lever-balance. The standard masses are often referred to, non-technically, as ''"weights"''. Since any variations in gravity will act equally on the unknown and the known weights, a lever-balance will indicate the same value at any location on Earth. Therefore, balance ''"weights"'' are usually calibrated and marked in [[质量|mass]] units, so the lever-balance measures mass by comparing the Earth's attraction on the unknown object and standard masses in the scale pans. In the absence of a gravitational field, away from planetary bodies (e.g. space), a lever-balance would not work, but on the Moon, for example, it would give the same reading as on Earth. Some balances can be marked in weight units, but since the weights are calibrated at the factory for standard gravity, the balance will measure standard weight, i.e. what the object would weigh at standard gravity, not the actual local force of gravity on the object.
If the actual force of gravity on the object is needed, this can be calculated by multiplying the mass measured by the balance by the acceleration due to gravity – either standard gravity (for everyday work) or the precise local gravity (for precision work). Tables of the gravitational acceleration at different locations can be found on the web.
'''Gross weight''' is a term that is generally found in commerce or trade applications, and refers to the total weight of a product and its packaging. Conversely, '''net weight''' refers to the weight of the product alone, discounting the weight of its container or packaging; and '''{{tsl|en|tare weight||tare weight}}''' is the weight of the packaging alone.
== 不同天体上的相对重量 ==
{{Main article|地球引力|表面重力}}
The table below shows comparative [[表面重力|gravitational accelerations at the surface]] of the Sun, the Earth's moon, each of the planets in the solar system. The “surface” is taken to mean the cloud tops of the [[气态巨行星|gas giants]] (Jupiter, Saturn, Uranus and Neptune). For the Sun, the surface is taken to mean the [[光球|photosphere]]. The values in the table have not been de-rated for the centrifugal effect of planet rotation (and cloud-top wind speeds for the gas giants) and therefore, generally speaking, are similar to the actual gravity that would be experienced near the poles.
{| class="wikitable" border="1"
|-
! 天体
! 地球重力<br>的倍数
! [[表面重力]]<br>m/s<sup>2</sup>
|-
| [[太阳]]
| 27.90
| 274.1
|-
| [[水星]]
| 0.3770
| 3.703
|-
| [[金星]]
| 0.9032
| 8.872
|-
| [[地球]]
| 1 （定义）
| 9.8226{{noteTag|1=这个值排除了地球自转导致的离心力的影响，因此大于9.806 65 <math>m/s^2</math>（[[标准重力]]）}}
|-
| [[月球]]
| 0.1655
| 1.625
|-
| [[火星]]
| 0.3895
| 3.728
|-
| [[木星]]
| 2.640
| 25.93
|-
| [[土星]]
| 1.139
| 11.19
|-
| [[天王星]]
| 0.917
| 9.01
|-
| [[海王星]]
| 1.148
| 11.28
|-
|}
-->
== 延伸阅读 ==
* [[体重]]
== 注释 ==
{{noteFoot}}
== 参考资料 ==
{{reflist|2|refs=
<ref name="Morrison">{{cite journal
|title=Weight and gravity - the need for consistent definitions
|author=Richard C. Morrison
|journal={{tsl|en|The Physics Teacher||The Physics Teacher}}
|volume=37 |page=51 |date=1999 |doi=10.1119/1.880152
|bibcode = 1999PhTea..37...51M }}</ref>
<ref name="Galili">{{cite journal
|title=Weight versus gravitational force: historical and educational perspectives
|author=Igal Galili
|journal=International Journal of Science Education
|volume=23 |page=1073 |date=2001 |doi=10.1080/09500690110038585
|bibcode = 2001IJSEd..23.1073G }}</ref>
<ref name="Gat">{{cite book |title=Standardization of Technical Terminology: Principles and Practice – ''second volume'' |editor=Richard Alan Strehlow |date=1988 |publisher=[[美国材料和试验协会|ASTM International]] |isbn=978-0-8031-1183-7 |chapter=The weight of mass and the mess of weight |last=Gat |first=Uri |pages=45–48 |url=https://books.google.com/books?id=CoB5w9Km0mUC&pg=PA45}}</ref>
<ref name="Canada">The National Standard of Canada, CAN/CSA-Z234.1-89 Canadian Metric Practice Guide, January 1989:
*'''5.7.3''' Considerable confusion exists in the use of the term "weight." In commercial and everyday use, the term "weight" nearly always means mass. In science and technology "weight" has primarily meant a force due to gravity. In scientific and technical work, the term "weight" should be replaced by the term "mass" or "force," depending on the application.
*'''5.7.4''' The use of the verb "to weigh" meaning "to determine the mass of," e.g., "I weighed this object and determined its mass to be 5 kg," is correct.</ref>
<ref name="Sur Das">{{cite web|author=Sur Das |url=http://warfare.atspace.eu/Moghul/Baburnama/Weighing_Grain.htm |title=Weighing Grain |date=1590s |work=Baburnama |archiveurl = http://archive.fo/hYPTy |archivedate = 2013-07-14 |deadurl = yes}}</ref>
<ref name="King">{{cite journal
|title=Weight and weightlessness
|author=Allen L. King
|journal={{tsl|en|American Journal of Physics||American Journal of Physics}} |volume=30 |page=387 |date=1963 |doi=10.1119/1.1942032
|bibcode = 1962AmJPh..30..387K }}</ref>
<ref name="French">{{cite journal |title=On weightlessness |author=A. P. French |journal={{tsl|en|American Journal of Physics||American Journal of Physics}} |volume=63 |pages=105–106 |date=1995 |doi=10.1119/1.17990|bibcode = 1995AmJPh..63..105F }}</ref>
<ref name="Galili-Lehavi">{{cite journal |last1=Galili |first1=I. |last2=Lehavi |first2=Y. |date=2003 |title=The importance of weightlessness and tides in teaching gravitation |journal={{tsl|en|American Journal of Physics||American Journal of Physics}} |volume=71 |issue=11 |pages=1127–1135 |url=http://sites.huji.ac.il/science/stc/staff_h/Igal/Research%20Articles/Weight-AJP.pdf |doi=10.1119/1.1607336|bibcode = 2003AmJPh..71.1127G }}</ref>
<ref name = "JCGM/WG 2">{{cite book
|author=Working Group 2 of the Joint Committee for Guides in Metrology (JCGM/WG 2)
|title=International vocabulary of metrology — Basic and general concepts and associated terms (VIM) — Vocabulaire international de métrologie — Concepts fondamentaux et généraux et termes associés (VIM)
|url=http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2008.pdf
|date=2008 |edition=3rd |type=JCGM 200:2008 |publisher=[[国际度量衡局|BIPM]]
|at=Note 3 to Section 1.2
|language=English, French
|archiveurl = https://web.archive.org/web/20180127200534/https://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2008.pdf
|archivedate = 2018-01-27
|deadurl = no
}}</ref>
<ref name=taylor>{{cite book |editor=Barry N. Taylor |editor2=Ambler Thompson |title=The International System of Units (SI) |publisher=[[国家标准技术研究所|NIST]] |date=2008 |series=NIST Special Publication 330 |edition=2008 |page=52 |url=http://physics.nist.gov/Pubs/SP330/sp330.pdf |archiveurl = https://web.archive.org/web/20170622033951/http://physics.nist.gov/Pubs/SP330/sp330.pdf |archivedate = 2017-06-22 |deadurl =yes}}</ref>
<ref name="Halliday 2007 95">{{cite book |title=Fundamentals of Physics |volume=1 |first=David |last=Halliday |first2=Robert |last2=Resnick |first3=Jearl |last3=Walker |publisher= Wiley |date=2007 |edition=8th |page=95 |isbn= 978-0-470-04473-5}}</ref>
<ref name="3rdCGPM">{{cite web
|url=http://www.bipm.org/en/CGPM/db/3/2/
|title=Resolution of the 3rd meeting of the CGPM (1901)
|publisher=BIPM
|archiveurl = https://web.archive.org/web/20180117131214/https://www.bipm.org/en/CGPM/db/3/2/
|archivedate = 2018-01-17
|deadurl = no
}}</ref>
<ref name ="Chester">{{cite book |title = Mechanics |author1 = Chester, W. |publisher = George Allen & Unwin. |location = London |date = 1979 |ISBN = 0-04-510059-4 |page = 83}}</ref>
<ref name ="Quantities and units">ISO 80000-4:2006, Quantities and units - Part 4: Mechanics</ref>
<ref name = "Bell, F.">{{cite book
|title=Principles of mechanics and biomechanics
|author=Bell, F.
|isbn=978-0-7487-3332-3
|url=https://books.google.com/books?id=bPcPnZQ36KwC&pg=PA174
|pages=174–176
|date=1998
|publisher=Stanley Thornes Ltd
}}</ref>
<ref name = "Galili, Igal">{{cite journal
|author = Galili, Igal
|title = Weight and gravity: teachers’ ambiguity and students’ confusion about the concepts
|journal = International Journal of Science Education
|volume = 15
|number = 2
|pages = 149–162
|date = 1993
|doi = 10.1080/0950069930150204
|bibcode = 1993IJSEd..15..149G }}</ref>
<ref name="NIST811wt">{{cite web |author=A. Thompson |author2=B. N. Taylor |last-author-amp=yes |title=The NIST Guide for the use of the International System of Units, Section 8: Comments on Some Quantities and Their Units |work=Special Publication 811 |url=http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=200349 |publisher=[[国家标准技术研究所|NIST]] |origyear = 2009-07-02 |date = 2010-03-03 |accessdate=2010-05-22|archiveurl = https://web.archive.org/web/20180130125355/http://ws680.nist.gov/publication/get_pdf.cfm?pub_id=200349 |archivedate = 2018-01-30 |deadurl = no}}</ref>
<ref name = "Hodgeman">{{cite book
| editor-last = Hodgeman
| editor-first = Charles
| title = Handbook of Chemistry and Physics
| edition = 44th
| publisher = Chemical Rubber Publishing Co.
| date = 1961
| location = Cleveland, USA
| 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]]