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*From*: John Denker <jsd@av8n.com>*Date*: Thu, 30 Jan 2020 13:25:44 -0700

One more thing:

This "should" be obvious, and we've discussed it before, but

here's a reminder. Most textbooks get this badly wrong. Even

Feynman gets it wrong.

There are *two* different concepts that we call "gravity".

Textbooks mercilessly switch back and forth between the

two meanings. No wonder students are confused.

There is no hope of understanding the Roche limit until

this is cleared up.

-- There is the extrinsic gravity, namely the acceleration

relative to some chosen local reference frame. I call

this /framative/ gravity since it is 100% frame-dependent.

This is commonly denoted g, but I recommend g_@F to make

explicit the dependence on the frame F.

-- Then there is the intrinsic, massogenic gravity. This

is what you calculate using the law of universal gravitation.

It is 100% frame-independent. I recommend denoting this

as δg or perhaps δg_M(r) since it depends on M and r.

For the next level of detail, see

https://www.av8n.com/physics/weight.htm#sec-various-notions

**References**:**[Phys-L] Roche limit***From:*Anthony Lapinski <alapinski@pds.org>

**Re: [Phys-L] Roche limit***From:*John Denker <jsd@av8n.com>

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