Weight: Difference between revisions

| image = WeeghaakMass versus weight in earth and mars.JPGsvg

| imagesize = x200px300px

| caption = A [[springdiagram scale]] measuresexplaining the weightmass ofand an object.weight

In [[science]] and [[engineering]], the '''weight''' of an object is a quantity associated with the [[gravitational force]] actingexerted on the object dueby other objects in its environment, although there is some variation and debate as to [[acceleration]]the orexact [[gravity]]definition.<ref name="Morrison">{{cite journal

Some standard textbooks<ref name='Knight'>{{Cite book|author=Knight, Randall D.|year=2004|title=Physics for Scientists and Engineers: a Strategic Approach|location=San Francisco, USAUS|publisher=Addison–Wesley|isbn=0-8053-8960-1|pages=100–101|url=https://archive.org/details/physicsforscien200knig}}</ref> define weight as a [[Euclidean vector|vector]] quantity, the [[gravitational force]] acting on the object. Others<ref name='Bauer-and-Westfall'>{{Cite book |authorfirst1=Bauer, Wolfgang and Westfall,|last1=Bauer |first2=Gary D. |last2=Westfall |year=2011 |title=University Physics with Modern Physics|location=New York|publisher=McGraw Hill|isbn=978-0-07-336794-1 |pages=103}}</ref><ref name='Serway-and-Jewett'>{{Cite book |authorfirst1=Serway, Raymond A. and Jewett,|last1=Serway |first2=John W. Jr.|last2=Jewett |year=2008 |title=Physics for Scientists and Engineers with Modern Physics|location=USAUS|publisher=Thompson|isbn=978-0-495-11245-7 |pages=106}}</ref> define weight as a scalar quantity, the magnitude of the gravitational force. Yet others<ref name='Hewitt'>{{Cite book|author=Hewitt, Paul G.|year=2001|title=Conceptual Physics|location=USAUS|publisher=Addison–Wesley|isbn=0-321-05202-1|pages=[https://archive.org/details/conceptualphysic00hewi_3/page/159 159]|url=https://archive.org/details/conceptualphysic00hewi_3/page/159}}</ref> define it as the magnitude of the [[reaction (physics)|reaction]] force exerted on a body by mechanisms that counteract the effects of gravity: the weight is the quantity that is measured by, for example, a spring scale. Thus, in a state of [[free fall]], the weight would be zero. In this sense of weight, terrestrial objects can be weightless: ignoringso if one ignores [[Drag (physics)|air resistance]], one could say the famouslegendary apple falling from the tree{{cn|date=March 2024}}, on its way to meet the ground near [[Isaac Newton]], would bewas weightless.

The [[unit of measurement]] for weight is that of [[force]], which in the [[International System of Units]] (SI) is the [[newton (unit)|newton]].<ref name="Morrison" /> For example, an object with a mass of one kilogram has a weight of about 9.8 newtons on the surface of the Earth, and about one-sixth as much on the [[Moon]]. Although weight and mass are scientifically distinct quantities, the terms are often confused with each other in everyday use (e.g. comparing and converting force weight in pounds to mass in kilograms and vice versa).<ref name="Canada">The National Standard of Canada, CAN/CSA-Z234.1-89 Canadian Metric Practice Guide, January 1989:

Further complications in elucidating the various concepts of weight have to do with the [[theory of relativity]] according to which gravity is modeled as a consequence of the [[curvature]] of [[spacetime]]. In the teaching community, a considerable debate has existed for over half a century on how to define weight for their students. The current situation is that a multiple set of concepts co-exist and find use in their various contexts.<ref name="Galili"/>

{{blockquote|"The weight ''W'' of a body is equal to the magnitude ''F_g'' of the gravitational force on the body."<ref name="Halliday 2007 95">{{cite book |title=Fundamentals of Physics |volume=1 |first1=David |last1=Halliday |first2=Robert |last2=Resnick |first3=Jearl |last3=Walker |publisher= Wiley |date=2007 |edition=8th |page=95 |isbn= 978-0-470-04473-5}}</ref>}}

{{Main|Mass versus weight}}[[File:WeightNormal.svg|thumb|250px|An object with mass ''m'' resting on a surface and the corresponding [[free body diagram]] of just the object showing the [[force]]s acting on it. NoticeThe that the amountmagnitude 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 [[mechanical equilibrium|equilibrium]] (all the forces and [[Moment (physics)|moments]] acting on it sum to zero).]]

| location = Cleveland, USAUS

| journal = NistNIST

The table below shows comparative [[Surface gravity|gravitational accelerations at the surface]] of the Sun, the Earth's moon, each of the planets in the solar system. The “surface”"surface" is taken to mean the cloud tops of the [[gasgiant giantsplanet]]s (Jupiter, Saturn, Uranus, and Neptune). For the Sun, the surface is taken to mean the [[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 gasgiant giantsplanets) and therefore, generally speaking, are similar to the actual gravity that would be experienced near the poles.