# Gravity model

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'''Gravity models''' are used in various [social sciences](/source/social_sciences) to predict and describe certain behaviors that mimic gravitational interaction as described in [Isaac Newton](/source/Isaac_Newton)'s laws of [gravity](/source/gravity).  Generally, the social science models contain some elements of [mass](/source/mass) and distance, which lends them to the metaphor of physical gravity. A gravity model provides an estimate of the volume of flows of, for example, goods, services, or people between two or more locations. This could be the movement of people between cities<ref>{{Cite journal|title = Modelling regional imbalances in English plebeian migration to late eighteenth-century London|journal = Economic History Review|volume = 71|issue = 3|date = 2017-07-27|doi = 10.1111/ehr.12569|first = Adam|last = Crymble|first2 = Adam|last2 = Dennett|first3 = Tim|last3 = Hitchcock|pages=747–771|url = http://sro.sussex.ac.uk/id/eprint/69500/4/Modelling%20Regional%20Imbalances.pdf|hdl = 2299/20290|hdl-access = free}}</ref> or the volume of trade between countries.

A gravity model cannot accurately predict flows, but is instead a measure against which actual observed values can be compared, highlighting where those flows are unexpectedly high or low. 

Social science gravity models:
* [Gravity model of trade](/source/Gravity_model_of_trade)
* [Trip distribution](/source/Trip_distribution)
* [Gravity model of migration](/source/Gravity_model_of_migration)
* [Two-step floating catchment area (2SFCA) method](/source/Two-step_floating_catchment_area_method)
* [Reilly's law of retail gravitation](/source/Reilly's_law_of_retail_gravitation)

==References==
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Adapted from the Wikipedia article [Gravity model](https://en.wikipedia.org/wiki/Gravity_model) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Gravity_model?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.