My textbook (Cengage Physics, 3rd ed, Mechanics-II, Pg-5.8) says that the gravitational mass of a body is affected by the presence of other bodies near it, whereas the inertial mass of a body remains unaffected by the presence of other bodies near it. How can that be true?
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1$\begingroup$ "Although inertial mass, passive gravitational mass and active gravitational mass are conceptually distinct, no experiment has ever unambiguously demonstrated any difference between them. " - en.wikipedia.org/wiki/Mass#Inertial_vs._gravitational_mass $\endgroup$– gandalf61Commented Apr 29 at 13:45
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1$\begingroup$ Maybe they're talking about gravitational binding energy. Or maybe they're just wrong and incompetent... $\endgroup$– PM 2RingCommented Apr 29 at 14:58
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1$\begingroup$ Certainly, taken out of context that statement is wrong. And it is not clear to me what context there could be which would make it ok. But I do not have that book so I cannot check $\endgroup$– DaleCommented Apr 29 at 15:39
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$\begingroup$ Yes, that's what I thought. It makes no sense, but it's in a highly reputable book. I searched for it on YouTube and found a video that supported this text: [youtu.be/z8I8IIVRQYo?si=ruz_Jrhjfae50rYi] $\endgroup$– Peter swiftCommented Apr 29 at 19:32
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1 Answer
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Could this just be a missunderstanding/ maybe a bit poorly formulated?
...the gravitational mass of a body is affected...
On second reading, this statement doesn't say "the gravitational mass is changing". It is "affected" may just mean that the gravitational force of the other body is "acting" on the gravitational mass of the first body.
This would be a perfectly normal statement within the framework of gravitational mass (response to gravitational forces, or "gravitational charge") and inertial mass (resistance to velocity changes), which would in succession state what @gandalf61 wrote, that both types are indistuingishable in experiment.
Maybe I'm wrong, but on first reading I read basically "other bodies change the gravitational mass of a body", which looked ridicolous. But now reading "other bodies interact with the gravitational mass of a body" is perfectly ok with me.
