- 5 days
You are correct that they orbit a mutual point, which is not the earth’s core, but actually outside of it, which is known as a barycenter
- 5 days
Not looking to fight just trying to understand. If that is true at a certain point then there is a position which both pulls are the greatest? And if something big enough or small enough passed through said point would it not feel the pull on both sides or get ripped apart if the object was weak enough?
That’s not really how gravity works. As you move closer to one object, the balance of gravitational forces will shift. If you move away from the earth and toward the moon, you’re going to eventually be pulled equally by both, leading to zero acceleration toward either.
In order for something to be pulled apart by two different gravitational forces, you’d need to be able to have a massive change in gravity over the distance of that object. For something planetary sized, this might be possible, but for anything on the scale of a human, you’d need something like a black hole event horizon to get enough of a force gradient to do damage.
Gravity is actually a pretty weak force compared to almost all other basic forces, and it doesn’t often get “concentrated” like other forces can.
If the moon-earth gravitational system was able to generate enough force to rip something apart at some specific point, space travel would certainly be a lot more interesting/daunting.
- Legianus@programming.devEnglish5 days
Astrophysicist here, I think you’d enjoy reading about the Hill Sphere and Roche limit. Not quite what you are asking for but comes close.
- 5 days
Not calling you a liar or anything but FUCK YOU. Now I can’t ask or debate anymore cause I am reading to much of the Hill Sphere and Roch limit. Your like a knowledge drug dealer…first hit is free. Then the next you have to pay for. All BS aside thank you for turning me on to these. Much love and have a happy 4th.
- 5 days
The barycenter of the earth and moon is outside Earth’s core, but still inside earth. On average (since it changes with mountains and such) about 1707 km deep. So technically earth itself is constantly going through that point without being ripped appart. The forces are strong enough to move water on earth’s surface though, this is what causes tides in the seas.
- 5 days
But with that there has to be a point where one or the other is the strongest or weakest? While they probably haven’t lined up or never will but it is safe to assume they will even for a millisecond.
- 5 days
You have to remeber that gravity is actually pretty weak, with exceptions that break our understanding of reality. So gravity can’t usually pull apart the strong nuclear force, which keeps quarks together, at least to my knowledge
- 5 days
You’re thinking about lagrange points – the places in a (dissimilar?) two-body system where the gravitational pull (and kinetic energy?) from both is equal and thus relatively stable.
Not a physicist, obviously.
Also, be aware that the effect of gravity diminishes with distance. We’re pulled towards the earth at about 9.8m/s/s here on the surface, but as you get further away that 9.8 drops off on an exponential curve.
This gives me a chance to repeat the best argument for why Star Wars is higher tech than Star Trek. When the enterprise gets to a planet they orbit, and the artificial gravity is only an internal issue. In star wars we see gravity shift as ships list due to damage or even fall towards planets, because they aren’t orbiting; they’re just hovering above the planet, presumably with their artificial gravity just working enough to stop the ship itself from falling.
- 5 days
Not a physics major here, but that would have to be exceptionally weak to be pulled apart as I see it. Even on the surface of earth you can hold a piece of tissue paper up and effectively neutralize the force of gravity without it pulling itself apart.
The bonds holding the molecules together would have to be weaker than the force of gravity pulling them apart, which would essentially make it into a gas I suppose.
- 5 days
Keep in mind that the answers given so far are true for a two body system. The system is unstable if there are three or more bodies (i.e. the sun, Jupiter…). There is a possibility that the moon will crash into the Earth.
- 5 days
The moon is receding from the Earth and would eventually roughly double its orbital period, while Earth’s rotation would nearly stop (one rotation every 47 days), and both would be tidally locked to the other. The same side of the Earth would always face the moon, and the same side of the moon would always face the Earth (as happens currently).
This is all assuming the system would continue unperturbed forever, however, it won’t. Before the above happens, the sun will turn into a red giant and the drag from the expanded atmosphere will slow down the orbits of both the Earth and Moon, eventually leading to them both ceasing to exist - the moon from reaching the Roche limit above the Earth, and the the Earth from entering the Sun’s photosphere and eventually spiraling into the core.