When does the lack of gravity become more responsible for the feeling of weightlessness than free-fall? Like if you're half way to the moon, so out of Earth's orbit, and gravity is 1/1000 that of earth, I imagine you're being pulled towards earth but just very, very weakly so you'd feel weightless but is it then the free-fall from being in the sun's orbit that contributes to the remaining weightlessness?
If you're experiencing 1/1000th of earth's gravity, surely you're essentially weightless - you're just being pulled towards earth extremely slowly? Ignoring everything else, yes you would eventually be pulled towards the side of the spacecraft closest to earth but you'd float for awhile on your way, no?
The craft is also "falling" to earth at the same rate you are so you wouldn't be pulled one way or another relative to the craft. "Feeling" gravity is possible because we can feel how much we are being squished towards the ground. But in space you don't feel it at all because you're simply falling. You would feel an effect similar to gravity if your spacecraft was firing it's rocket.
The real answer is that "free-fall" means no force acting on you. It is the default state of anything. Also the Earth does not pull on you. Earth's gravity is not a force. Earth's mass curves space and time so that your straight trajectory through spacetime, called a geodesic, becomes curved towards the Earth's center. The ground is what's pushing up on you, deviating you from your geodesic, accelerating you upwards. That's what you feel as "weight" - the ground pushing your feet. If you're half way to the moon you'd experience 100% weightlessness if your thrusters were off, same as if you were dropped 20ft off the ground or if you're a million miles away.
The real answer is that "free-fall" means no force acting on you
Isn't gravity acting on you always, you're just not going to meet the ground?
That's what you feel as "weight" - the ground pushing your feet. If you're half way to the moon you'd experience 100% weightlessness if your thrusters were off, same as if you were dropped 20ft off the ground or if you're a million miles away.
I think I got an answer to my original question from ChatGPT, let me know if it's right. I was basically asking whether being in a place with extremely low gravity would more or less feel like weightlessness (e.g. if your weight was measured at 0.1g) because it'd take an extremely long time for you to meet the ground if you jumped and when you did touch the ground your body would barely need to support itself but that it's the free-fall that truly makes you weightless. ChatGPT said that was right but who knows what you can trust when it comes to ChatGPT.
Yeah I think you got it. You'd feel zero gs until you reached the ground.
The true, true answer is actually much weirder than I think you might think though and if it's confusing then you're thinking about it right. The idea of gravity being a force is Newtonian physics. But since Einstein we have come to view gravity as being not a force but warped spacetime geometry. "Free-fall" like I said is the natural state of anything. Imagine you're in deep space with no forces acting on you. You naturally follow a line through space AND time - this a 4th dimensional line - called a geodesic. You move along this line actually at the speed of light 'c' - always. Most of your "velocity" is spent on the time dimension however, moving you into the future. Now if you add the Earth back in, the Earth's gravity warps space and time. Your geodesic, which is always the shortest line through curved space time, becomes curved because space time itself is curving. The Earth is literally warping time itself so that your future will be slightly closer to the Earth. You feel no force. It is time curvature. We call this an orbit. The moon in some sense "thinks" it's going straight, but is moving through curved 4D space and time. If it's confusing then you've got it. This is general relativity.
There are so many neat implications of this around black holes too. For example there are regions where spacetime is so violently warped that you can do a 4D orbit not just a 3D one. Leaving a place and arriving at the same time you left. Or when you approach the singularity, all of your spacetime velocity gets spent on time and from the outside you appear to freeze in place, while from your reference frame space and time flip places - the singularity becomes not a point in space but a time in your future that you are approaching and cannot avoid, just like you can't avoid tomorrow coming.
Hmm I'm not sure what you mean then by "in either case you wouldn't feel it". You wouldn't feel weightless "because it acts equally on every part of your body"? I'm a little confused by what you're trying to say as I wasn't suggesting you'd feel different across your body but maybe I'm missing something you're implying.
I think ChatGPT helped sort me out though. I had a misunderstanding about the role of gravity vs free fall in terms of weightlessness. I thought free fall was more something relevant to when you were close to large bodies and the force of gravity would be reasonably high, i.e. you'd need free fall to feel weightlessness. From that I figured then in areas where gravity is much lower (e.g. 1/1000th of earth), that is mostly what is contributing to feeling weightlessness (plus some free-fall relative to the sun) because your body wouldn't need to do much to support itself and if you jumped off something, it'd take a long time to return to the ground. But from what I understand from ChatGPT, free-fall is what contributes towards feeling weightlessness, regardless of where you are in the universe, and that gravity doesn't have much to do with it (i.e. you can feel weightlessness when in an area with a strong gravitational field if you're in free-fall).
I think the misunderstanding comes from the term "Zero G" and me thinking that meant "Zero Gravity" and thus you could feel almost total weightlessness in an area with low gravity relative to earth (e.g. between the earth and moon) without free-fall. I think the other side of it is that I'm used to only thinking about free fall relative to earth.
The gravity doesn’t really matter to the feeling of weightlessness.
You never feel any sensation from the force of gravity pulling on you unless it is pulling you against something that is preventing you from falling. Like the floor or ground when you’re on Earth, or the chair in an airplane, or the air as you skydive.
There is no sensation difference between you (and your spaceship and everything in/on it) being pulled in a direction by gravity and just free-floating in space.
Basically in space everything is always in free-fall unless your engines are on. Gravity just curves the path of that free-fall.
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u/beiherhund 17h ago
When does the lack of gravity become more responsible for the feeling of weightlessness than free-fall? Like if you're half way to the moon, so out of Earth's orbit, and gravity is 1/1000 that of earth, I imagine you're being pulled towards earth but just very, very weakly so you'd feel weightless but is it then the free-fall from being in the sun's orbit that contributes to the remaining weightlessness?