6 ms·

One of the things I've always been curious about - gravity is still very much exerting force on things in orbit, it's just that the object is moving along the p

by RC_ITR 3y ago

One of the things I've always been curious about - gravity is still very much exerting force on things in orbit, it's just that the object is moving along the perpendicular axis just as fast. For someone smarter at physics than me - I get why this 'feels' like weightlessness/0G, but does it actually have that impact when it comes to physical manufacturing? If it does, wouldn't terrestrial factories that have some sort of inertial roller coaster in them (akin to a vomit comet) be the cheaper/better answer? EDIT: I think a lot of people are missing the point of my question here. Remember, objects in orbit are accelerating because they are changing direction. This is different that being motionless in a far field with microgravity. But in practice, does that acceleration matter for physical manufacturing?

JumpCrisscross 3y ago
> the object is moving along the perpendicular axis just as fast Orbit is free fall. It’s equally correct to describe a falling object’s weightlessness as moving as fast as gravity. > get why this 'feels' like weightlessness/0G, but does it actually have that impact when it comes to physical manufacturing No, it’s the first postulate of Einstein’s theory of special relativity [1]. Free fall and the absence of gravity are as indistinguishable as acceleration and the its presence. [1] https://en.m.wikipedia.org/wiki/Postulates_of_special_relativity https://en.m.wikipedia.org/wiki/Postulates_of_special_relati...
- twic 3y ago
  Known as the equivalence principle: https://en.wikipedia.org/wiki/Equivalence_principle https://en.wikipedia.org/wiki/Equivalence_principle In a curved orbit, that may be true at points, but for an extended object, tidal forces come into play: https://en.wikipedia.org/wiki/Tidal_force https://en.wikipedia.org/wiki/Tidal_force
f154hfds 3y ago
The 'feeling' of weightlessness is pretty much an indication of 0 (micro) gravity. Gravity always exerts a force, the problem is on Earth we have ground exerting an equal and opposite force contrary to gravity. When you feel weightless whether in orbit or just falling off a cliff you're in free fall experiencing none of that upward opposition to gravitational force. For example, it was very hard to replicate the moon's gravity when training pilots to land on the moon. How do you 'fake' a different gravity on Earth? It's pretty hard to do: https://www.youtube.com/watch?v=aw8kRZEvh_s https://www.youtube.com/watch?v=aw8kRZEvh_s EDIT: to your question about centripetal force, either you experience acceleration or you don't. Since gravity is in equilibrium with centripetal force relative to movement around Earth you shouldn't get acceleration from this. However, you will get micro g's from rotation of the station itself, etc.
- deleted 3y ago
  [deleted]
- RC_ITR 3y ago
  >centripetal force relative to movement around Earth you shouldn't get acceleration from this. If there is no acceleration, then how are objects changing direction?
  - f154hfds 3y ago
    The ISS will do a 360 degree rotation every 90 minutes to maintain its orientation relative to the surface of the Earth. This will result in bodies inside the ISS slowly rotating in the opposite direction of that rotation. However, this is unrelated to acceleration - these are constant angular velocities. The micro gravity I believe is the result of atmospheric drag, and the occasional boosting required to account for it. Also I should add, it is confusing thinking about 0g, because obviously bodies in a gravity well are experiencing a gravitational force. Really we're talking about 0 acceleration, where g is the acceleration due to gravity. In orbit this g acceleration is cancelled out by centripetal acceleration to produce 0 acceleration, or free fall.
    - heavenlyblue 3y ago
      Aren't bodies inside ISS rotating with it? Or are you implying that the rotation of ISS is not inertial but is constantly propelled by engines? If engines are driving it constantly, why is not constantly accelerating it's rotation?
      - f154hfds 3y ago
        True - thanks for the clarification. As long as the ISS is rotating at a constant rate anything oriented to it inside of it will not perceive it to be rotating. It's rotating relative to a stationary perspective on the surface of the Earth but by the time anything docks to it, everything in the system will be rotating at the same rate. Thanks for pointing this out!
    - 3y ago
nradov 3y ago
Terrestrial factories for round lead shot do something like that. Just drop molten lead from the top of a tower and it will form a near perfect sphere as it falls weightless. https://en.wikipedia.org/wiki/Shot_tower https://en.wikipedia.org/wiki/Shot_tower
narag 3y ago
I think a lot of people are missing the point of my question here. I believe it's you who are missing the point. Acceleration is irrelevant, it's how it's transmitted that matters. You feel gravity because the ground prevents you from falling exerting an opposite force, that is transmitted mechanically along your body. There is no difference between free falling and no gravity except in monster gravitational fields like the one close to an event horizon where differential gravity (tide) could torn you apart. In any other situation you can safely assume that all the points in an object are pulled uniformly.
- RC_ITR 3y ago
  Direction is a fundamental aspect of acceleration, no? I'm also not asking about what our brains are conditioned to feel. I am simply asking - is the constant acceleration of orbit fundamentally different than no acceleration, even if both would feel the same? No-one has answered that in a compelling way. Because to be clear - in one, no forces are being applied and in another, there are forces being applied (how else would you change directions?).
  - narag 3y ago
    I'm also not asking about what our brains are conditioned to feel. Brain can't feel without senses input. is the constant acceleration of orbit fundamentally different than no acceleration...? No. how else would you change directions? You don't. You keep going straight, space is deformed by gravity. But even if you look at it like in classical mechanics, the effect is applied uniformly to every particle of your body, so it makes no difference. Ask yourself this: how do you feel gravity right now?
    - RC_ITR 3y ago
      >No. Ok but why? >You don't. You keep going straight, space is deformed by gravity. Yeah, and if gravity weren't deforming the space, objects otherwise in orbit would move differently. That's just changing the mechanics (presumably in an attempt to appear more knowledgeable?) to avoid the question of why two wildly different scenarios (no forces vs. offsetting forces) are the exact same. >But even if you look at it like in classical mechanics, the effect is applied uniformly to every particle of your body, so it makes no difference. Again, my question is why in your model is the uniform application of a force the same as no application of a force? >Ask yourself this: how do you feel gravity right now? You don't have a sense for your own weight? I do and I don't know how to describe that feeling beyond that. If I were in a true extremely low gravity situation (like deep space) I would feel differently.
wildzzz 3y ago
Assume the earth is a perfectly smooth sphere with a constant force of gravity and there is no air resistance: Throw a ball parallel to the ground. Now throw it faster. It will land farther away than last time, right? Keep throwing it faster and faster and the ball will keep landing further and further away from you. Eventually, you throw it so fast that the ball flys through the air, all the way around the earth and lands back at your feet from behind you. You've just completed a single orbit around the earth. Keep throwing it faster and faster until the ball flies past you forever without touching the ground. This is a little hard to imagine because this speed is tremendous and something no one can really experience on earth. The ball is constantly falling away from that direction you threw it originally due to gravity. Gravity is always acting on the ball and is always acting on any satellite in space as well. Gravity doesn't change that much for how high satellites fly. However the speed of the ball is just so such that it will never change from the height you originally threw it from. Catch the ball out of the air and throw it just a little faster this time. The ball will still orbit but will pass over your head this time. The speed of the ball dictates the orbit altitude. Mass also factors in as well but not much for something so small. Grab it out of the air and keep throwing it faster and faster and eventually, the speed is able to overcome gravity and the ball leaves Earth's gravity entirely. In Low Earth Orbit, there is just enough atmosphere to provide some minor air resistance that will actually slow down that ball you threw. As the ball slows, the orbit altitude decreases. As the altitude decreases, the atmosphere gets thicker and air resistance increases which makes the ball slow even more. It gets so slow that it can't maintain an orbit any more so it lands on the surface. If you attach a small rocket engine to the back of the ball, you can occasionally turn it on to maintain the exact speed you need for that orbit. If you use the rocket engine to make the ball go faster, you can raise the orbit. Rotate the ball 180deg and now you can use the rocket engine to slow the ball to lower the orbit. Astronauts in space constantly have gravity on them but they are moving at such high speeds that gravity is not able to change their altitude. They are always "falling" just like the ball but never land. They float around inside their spacecraft because those too are falling constantly.
- lloeki 3y ago
  IOW orbital mechanics is the art of falling whilst constantly missing the ground

by RC_ITR 3y ago

JumpCrisscross 3y ago

> the object is moving along the perpendicular axis just as fast Orbit is free fall. It’s equally correct to describe a falling object’s weightlessness as moving as fast as gravity. > get why this 'feels' like weightlessness/0G, but does it actually have that impact when it comes to physical manufacturing No, it’s the first postulate of Einstein’s theory of special relativity [1]. Free fall and the absence of gravity are as indistinguishable as acceleration and the its presence. [1] https://en.m.wikipedia.org/wiki/Postulates_of_special_relativity https://en.m.wikipedia.org/wiki/Postulates_of_special_relati...

twic 3y ago
Known as the equivalence principle: https://en.wikipedia.org/wiki/Equivalence_principle https://en.wikipedia.org/wiki/Equivalence_principle In a curved orbit, that may be true at points, but for an extended object, tidal forces come into play: https://en.wikipedia.org/wiki/Tidal_force https://en.wikipedia.org/wiki/Tidal_force

f154hfds 3y ago

The 'feeling' of weightlessness is pretty much an indication of 0 (micro) gravity. Gravity always exerts a force, the problem is on Earth we have ground exerting an equal and opposite force contrary to gravity. When you feel weightless whether in orbit or just falling off a cliff you're in free fall experiencing none of that upward opposition to gravitational force. For example, it was very hard to replicate the moon's gravity when training pilots to land on the moon. How do you 'fake' a different gravity on Earth? It's pretty hard to do: https://www.youtube.com/watch?v=aw8kRZEvh_s https://www.youtube.com/watch?v=aw8kRZEvh_s EDIT: to your question about centripetal force, either you experience acceleration or you don't. Since gravity is in equilibrium with centripetal force relative to movement around Earth you shouldn't get acceleration from this. However, you will get micro g's from rotation of the station itself, etc.

deleted 3y ago
[deleted]
RC_ITR 3y ago
>centripetal force relative to movement around Earth you shouldn't get acceleration from this. If there is no acceleration, then how are objects changing direction?
- f154hfds 3y ago
  The ISS will do a 360 degree rotation every 90 minutes to maintain its orientation relative to the surface of the Earth. This will result in bodies inside the ISS slowly rotating in the opposite direction of that rotation. However, this is unrelated to acceleration - these are constant angular velocities. The micro gravity I believe is the result of atmospheric drag, and the occasional boosting required to account for it. Also I should add, it is confusing thinking about 0g, because obviously bodies in a gravity well are experiencing a gravitational force. Really we're talking about 0 acceleration, where g is the acceleration due to gravity. In orbit this g acceleration is cancelled out by centripetal acceleration to produce 0 acceleration, or free fall.
  - heavenlyblue 3y ago
    Aren't bodies inside ISS rotating with it? Or are you implying that the rotation of ISS is not inertial but is constantly propelled by engines? If engines are driving it constantly, why is not constantly accelerating it's rotation?
    - f154hfds 3y ago
      True - thanks for the clarification. As long as the ISS is rotating at a constant rate anything oriented to it inside of it will not perceive it to be rotating. It's rotating relative to a stationary perspective on the surface of the Earth but by the time anything docks to it, everything in the system will be rotating at the same rate. Thanks for pointing this out!
  - 3y ago

nradov 3y ago

Terrestrial factories for round lead shot do something like that. Just drop molten lead from the top of a tower and it will form a near perfect sphere as it falls weightless. https://en.wikipedia.org/wiki/Shot_tower https://en.wikipedia.org/wiki/Shot_tower

narag 3y ago

I think a lot of people are missing the point of my question here. I believe it's you who are missing the point. Acceleration is irrelevant, it's how it's transmitted that matters. You feel gravity because the ground prevents you from falling exerting an opposite force, that is transmitted mechanically along your body. There is no difference between free falling and no gravity except in monster gravitational fields like the one close to an event horizon where differential gravity (tide) could torn you apart. In any other situation you can safely assume that all the points in an object are pulled uniformly.

RC_ITR 3y ago
Direction is a fundamental aspect of acceleration, no? I'm also not asking about what our brains are conditioned to feel. I am simply asking - is the constant acceleration of orbit fundamentally different than no acceleration, even if both would feel the same? No-one has answered that in a compelling way. Because to be clear - in one, no forces are being applied and in another, there are forces being applied (how else would you change directions?).
- narag 3y ago
  I'm also not asking about what our brains are conditioned to feel. Brain can't feel without senses input. is the constant acceleration of orbit fundamentally different than no acceleration...? No. how else would you change directions? You don't. You keep going straight, space is deformed by gravity. But even if you look at it like in classical mechanics, the effect is applied uniformly to every particle of your body, so it makes no difference. Ask yourself this: how do you feel gravity right now?
  - RC_ITR 3y ago
    >No. Ok but why? >You don't. You keep going straight, space is deformed by gravity. Yeah, and if gravity weren't deforming the space, objects otherwise in orbit would move differently. That's just changing the mechanics (presumably in an attempt to appear more knowledgeable?) to avoid the question of why two wildly different scenarios (no forces vs. offsetting forces) are the exact same. >But even if you look at it like in classical mechanics, the effect is applied uniformly to every particle of your body, so it makes no difference. Again, my question is why in your model is the uniform application of a force the same as no application of a force? >Ask yourself this: how do you feel gravity right now? You don't have a sense for your own weight? I do and I don't know how to describe that feeling beyond that. If I were in a true extremely low gravity situation (like deep space) I would feel differently.

wildzzz 3y ago

Assume the earth is a perfectly smooth sphere with a constant force of gravity and there is no air resistance: Throw a ball parallel to the ground. Now throw it faster. It will land farther away than last time, right? Keep throwing it faster and faster and the ball will keep landing further and further away from you. Eventually, you throw it so fast that the ball flys through the air, all the way around the earth and lands back at your feet from behind you. You've just completed a single orbit around the earth. Keep throwing it faster and faster until the ball flies past you forever without touching the ground. This is a little hard to imagine because this speed is tremendous and something no one can really experience on earth. The ball is constantly falling away from that direction you threw it originally due to gravity. Gravity is always acting on the ball and is always acting on any satellite in space as well. Gravity doesn't change that much for how high satellites fly. However the speed of the ball is just so such that it will never change from the height you originally threw it from. Catch the ball out of the air and throw it just a little faster this time. The ball will still orbit but will pass over your head this time. The speed of the ball dictates the orbit altitude. Mass also factors in as well but not much for something so small. Grab it out of the air and keep throwing it faster and faster and eventually, the speed is able to overcome gravity and the ball leaves Earth's gravity entirely. In Low Earth Orbit, there is just enough atmosphere to provide some minor air resistance that will actually slow down that ball you threw. As the ball slows, the orbit altitude decreases. As the altitude decreases, the atmosphere gets thicker and air resistance increases which makes the ball slow even more. It gets so slow that it can't maintain an orbit any more so it lands on the surface. If you attach a small rocket engine to the back of the ball, you can occasionally turn it on to maintain the exact speed you need for that orbit. If you use the rocket engine to make the ball go faster, you can raise the orbit. Rotate the ball 180deg and now you can use the rocket engine to slow the ball to lower the orbit. Astronauts in space constantly have gravity on them but they are moving at such high speeds that gravity is not able to change their altitude. They are always "falling" just like the ball but never land. They float around inside their spacecraft because those too are falling constantly.

lloeki 3y ago
IOW orbital mechanics is the art of falling whilst constantly missing the ground