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In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar quantity, the magnitude of the gravitational force. Others define it as the magnitude of the reaction force exerted on a body by mechanisms that keep it in place: 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: ignoring air resistance, the famous apple falling from the tree, on its way to meet the ground near Isaac Newton, would be weightless. The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton. 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 (i.e. comparing and converting force weight in pounds to mass in kilograms and vice versa). 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.
References
- Sur Das (1590s). "Weighing Grain". Baburnama. http://warfare.atspace.eu/Moghul/Baburnama/Weighing_Grain.htm.
- Igal Galili (2001). "Weight versus gravitational force: historical and educational perspectives". International Journal of Science Education 23: 1073. doi:10.1080/09500690110038585. Bibcode: 2001IJSEd..23.1073G. https://dx.doi.org/10.1080%2F09500690110038585
- http://www.averyweigh-tronix.com/museum accessed 29 March 2013.
- Gat, Uri (1988). "The weight of mass and the mess of weight". in Richard Alan Strehlow. Standardization of Technical Terminology: Principles and Practice – second volume. ASTM International. pp. 45–48. ISBN 978-0-8031-1183-7. https://books.google.com/books?id=CoB5w9Km0mUC&pg=PA45.
- Allen L. King (1963). "Weight and weightlessness". American Journal of Physics 30: 387. doi:10.1119/1.1942032. Bibcode: 1962AmJPh..30..387K. https://dx.doi.org/10.1119%2F1.1942032
- A. P. French (1995). "On weightlessness". American Journal of Physics 63: 105–106. doi:10.1119/1.17990. Bibcode: 1995AmJPh..63..105F. https://dx.doi.org/10.1119%2F1.17990
- Galili, I.; Lehavi, Y. (2003). "The importance of weightlessness and tides in teaching gravitation". American Journal of Physics 71 (11): 1127–1135. doi:10.1119/1.1607336. Bibcode: 2003AmJPh..71.1127G. http://sites.huji.ac.il/science/stc/staff_h/Igal/Research%20Articles/Weight-AJP.pdf.
- Richard C. Morrison (1999). "Weight and gravity - the need for consistent definitions". The Physics Teacher 37: 51. doi:10.1119/1.880152. Bibcode: 1999PhTea..37...51M. https://dx.doi.org/10.1119%2F1.880152
- "Resolution of the 3rd meeting of the CGPM (1901)". BIPM. http://www.bipm.org/en/CGPM/db/3/2/.
- Chester, W. Mechanics. George Allen & Unwin. London. 1979. ISBN:0-04-510059-4. Section 3.2 at page 83.
- ISO 80000-4:2006, Quantities and units - Part 4: Mechanics
- Bell, F. (1998). Principles of mechanics and biomechanics. Stanley Thornes Ltd. pp. 174–176. ISBN 978-0-7487-3332-3. https://books.google.com/books?id=bPcPnZQ36KwC&pg=PA174.
- Galili, Igal (1993). "Weight and gravity: teachers’ ambiguity and students’ confusion about the concepts". International Journal of Science Education 15 (2): 149–162. doi:10.1080/0950069930150204. Bibcode: 1993IJSEd..15..149G. https://dx.doi.org/10.1080%2F0950069930150204
- 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.
- A. Thompson; B. N. Taylor (March 3, 2010). "The NIST Guide for the use of the International System of Units, Section 8: Comments on Some Quantities and Their Units". Special Publication 811. NIST. http://physics.nist.gov/Pubs/SP811/sec08.html#8.3. Retrieved 2010-05-22.
- Hodgeman, Charles, ed (1961). Handbook of Chemistry and Physics (44th ed.). Cleveland, USA: Chemical Rubber Publishing Co.. pp. 3480–3485.
- Clark, John B (1964). Physical and Mathematical Tables. Oliver and Boyd.
- "Common Conversion Factors, Approximate Conversions from U.S. Customary Measures to Metric". National Institute of Standards and Technology. https://www.nist.gov/pml/wmd/metric/common-conversion-b.cfm. Retrieved 2013-09-03.
- This value excludes the adjustment for centrifugal force due to Earth’s rotation and is therefore greater than the 9.80665 m/s2 value of standard gravity.
