What would gravity feel like at different points on Earth if there was a super massive object near Earth?

I know it would depend on the mass of the object, but what I'm wondering is could there be a scenario where gravity appeared to be zero at any of the points on Earth?

For example, could point B ever feel like they're in freefall? Or would they simply feel 1G? (Earth and everything on it may be in "freefall" toward the black hole, but Earth still exerts its own gravity?)

what is the felt gravity at A, B and C?

I'm assuming that Earth is not orbiting the black hole, or the other way around. I'm not making assumptions of distance or mass, I'm more wondering if we could tweak the assumptions about distance or mass to get a zero-G effect at any point on Earth.

  • $\begingroup$ So you assume that Earth is falling into the black hole? $\endgroup$ – Qmechanic Nov 13 '19 at 9:59

Considering how gravity is an attractive force, point B can never experience $0$ gravitational field since the gravitational force from both bodies points in the same direction there. A person at B would just feel heavier than if they would without the other body there.

Additionally, for two forces to cancel out they need to act along the same line, therefore point C is out as well. Someone there would feel a pull that is not completely towards the center of the Earth though.

However, at point A the forces could definitely cancel out. It just depends on the mass of the two bodies and their separation.

I will also note that "free fall" does not mean "no gravitational force", as it seems like your answer hints at that idea.

  • $\begingroup$ So you're saying that if the black hole was massive enough, a person at point A could stop feeling Earth's gravity? This seems weird to me, because objects of different mass fall in gravity at the same rate. So wouldn't both person A and Earth be falling at the same rate towards the black hole? And if so, wouldn't person A still feel Earth's gravity as they are both falling towards the black hole? Or could a person at point A actually be lifted from the surface of Earth? $\endgroup$ – chris c Nov 11 '19 at 18:52
  • $\begingroup$ @chrisc I am saying at point A the gravity from the Earth could be canceled by the gravity of the black hole. I didn't say anything about the orbits. That depends on initial conditions of the orbits. I am merely talking about forces here. Not motion due to those forces. $\endgroup$ – Aaron Stevens Nov 11 '19 at 19:04
  • $\begingroup$ I made the edit about orbits in response to Qmechanics's comment. What I'm asking about your comment is why gravity could be canceled at point A. I'm imagining holding a bowling ball and a marble and dropping them. They both fall at the same rate. So, wouldn't person A and Earth be falling towards the black hole at the same rate? And since they'd both be falling toward the black hole at the same rate, wouldn't person A still just feel 1G pointed into the center of Earth? $\endgroup$ – chris c Nov 11 '19 at 19:18
  • $\begingroup$ @chrisc Gravity is a vector quantity. If the gravity magnitude at point A due to Earth is equal to the gravity magnitude at point A due to the black hole, then these forces are going to cancel because they point in opposite directions. $\mathbf F_g-\mathbf F_g=0$ This has nothing to do with the motion of anything. It is true for forces, because forces are vectors. What happens because of the forces depends on what the objects are doing at that time. Since you do not care about that part, I have not addressed it in my answer. $\endgroup$ – Aaron Stevens Nov 11 '19 at 19:29
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    $\begingroup$ ...If the BH was so close that the tidal force would actually lift the person off the ground, then it probably also would be close enough to start ripping the Earth apart. The Earth is not a solid body. It's mostly soft and squishy, with a hard rocky crust, and a hard iron pit in the center. en.wikipedia.org/wiki/Spaghettification $\endgroup$ – Solomon Slow Nov 11 '19 at 20:05

We have a massive object near Earth: the Moon. It causes tides but I do not feel lighter at high tide nor heavier at low tide. If an object nearby is heavy enough so that I feel a weight difference I will probably drown in a monster tidal flood.


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