# Gravity calculations I should be able to do

**URL:** <https://boards.straightdope.com/t/gravity-calculations-i-should-be-able-to-do/604776>\
**Category:** Factual Questions\
**Created:** [December 2, 2011, 1:38am UTC](https://boards.straightdope.com/t/gravity-calculations-i-should-be-able-to-do/604776 "2011-12-02T01:38:54Z")\
**Posts on this page:** 5\
**Page:** 3

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**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\
**Post date:** [December 4, 2011, 3:30am UTC](https://boards.straightdope.com/t/gravity-calculations-i-should-be-able-to-do/604776/41 "2011-12-04T03:30:58Z")

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> [@](#):
>
> Actually, you always have to take both masses into account, unless one is so much more massive than the other that it doesn’t matter to the accuracy of solving the problem. (A bowling ball falling towards the earth.)

Unless you’re working to extreme precision, the Earth falling into (or around) the Sun is also such a case. Heck, even Jupiter is less than 1% the mass of the Sun.

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**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\
**Post date:** [December 4, 2011, 4:07am UTC](https://boards.straightdope.com/t/gravity-calculations-i-should-be-able-to-do/604776/42 "2011-12-04T04:07:35Z")

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> [@iamnotbatman](#):
>
> If you picture the motion to be a circle on the X-Y axis with radius 1 AU, then when the earth is at X=1, you can see that Y=0. Go a quarter of the way around, then X=0, and Y=1. The point is to think of the earth as “falling” from X=1 to X=0, ignoring the Y-coordinate.

Thanks. Got it.

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**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\
**Post date:** [December 4, 2011, 4:10am UTC](https://boards.straightdope.com/t/gravity-calculations-i-should-be-able-to-do/604776/43 "2011-12-04T04:10:27Z")

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> [@SlowMindThinking](#):
>
> … Both objects are perpetually falling towards that center of mass but, Adamseque, they just keep missing.

Got your point, but I don’t get reference “Adamseque.” Sounds nice. What is it?

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**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\
**Post date:** [December 4, 2011, 4:15am UTC](https://boards.straightdope.com/t/gravity-calculations-i-should-be-able-to-do/604776/44 "2011-12-04T04:15:27Z")

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“Adamsesque”: “In a manner reminiscent of that described by Douglass Adams”. In the _Hitchhikers’ Guide to the Galaxy_ books, he explains that the secret to flying is to throw yourself at the ground, but miss.

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**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\
**Post date:** [August 3, 2018, 3:00pm UTC](https://boards.straightdope.com/t/gravity-calculations-i-should-be-able-to-do/604776/45 "2018-08-03T15:00:06Z")

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Just learned the term for this calculation - “free-fall time”. This article confirms the calculations we made above and talks about other uses for it [Free-fall time - Wikipedia](https://en.wikipedia.org/wiki/Free-fall_time)

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