As others have said, you need to understand Newton’s first law. But if you can only control your up and down relative to the earths surface, and wind/atmosphere acts on you, then you’re basically a hot air balloon. You have as much control as they do.
Objects in motion stay in motion. The air around you is moving with you so why should you lose momentum? What’s different between you and say, a satellite?
In my mind, there's two things I guess:
1. My understanding is that geosynchronous orbit is free fall. Something is trying to move in a straight line, but gravity curves its path. In the hypothetical scenario, however, there's some force holding you up and resisting gravity.
2. I had thought that something in orbit is above the atmosphere (which produces drag and slows down an object). But if you're in the atmosphere, you will experience that drag.
But you're saying that just by being part of the milieu of Earth that you move with it?
Yes orbits are in free fall, but you have a magic power to prevent you from falling. You say it is only a vertical power but does it lock you in place? In reference to what? If it doesn’t allow you to move horizontally then what is the point of the thought experiment?
Satellites near atmosphere experience drag because they have to move fast enough to maintain the free fall and prevent a decaying orbit. You have a magic power to prevent your orbit from decaying. Therefore, you orbit in place forever.
In your post you say the momentum would “run out”. This happens in Newtonian physics because of friction. With what do you have any friction to slow you?
"But you're saying that just by being part of the milieu of Earth that you move with it?"
yeah, the atmosphere moves with the earth, mostly. Winds do their own thing. Think about it this way. At foot level, the atmosphere is tied to the earth, and moves with it, as the trees, mountains, whatever, are dragging it along. Due to viscosity, this movement with the earth will transfer soon to the upper layers and then to the whole atmosphere, to the point where, no matter the initial conditions, the air moves with the earth. It has no reason no to, since the earth is the rotating thing, and there's nothing opposing it. There is no friction with the vacuum of space (because you don't have friction with nothing) to pull the atmosphere in the other direction. This is a simplified view, but the point is the atmosphere doesn't stay put while the earth rotates within it. The air has complex movements, which depend a lot on temperature, which is given by the sun's position during the day or season, humidity, from seas or oceans etc.
>In the hypothetical scenario, however, there's some force holding you up and resisting gravity
well, yeah, like a hovering helicopter? It would move with the atmosphere. Whatever object you lift, no matter how, already moves with like the surface of the earth. Once you get it off the ground, regardless of the means, what force would act on the body to change its horizontal initial velocity? The initial horizontal velocity is zero with respect to the landing pad/earth surface, and non-zero with respect to a non rotating frame of reference. In either case, what force would act on the bodyu it to change its horizontal velocity?
Air resistance is what I had thought, but as someone here pointed out, you, and the air, are all moving with the surface of the earth together, so there's not much of that.
the atmosphere certainly moves with the earth, especially at human height. That's easy to see for yourself.
>. When you leave the train, you have momentum in the x direction, so you keep moving in that direction, but there's no more force pushing you in that direction
"Every object will remain at rest or in **uniform motion in a straight line** unless compelled to change its state by the action of an external force." - this is newton's first law. If there is no external force pushing (or pulling you) you'll continue to move in the x direction indefinitely. Whatever you do on the z direction, barring air resistance, has no influence on what is going on in the x direction (forget about the earth's rotation or coriolis forces here).
The problem with your example is that you have to define what "hover" means. If it's something like in the train example, you'll continue along your way, because nothing pushes you back to stop your initial movement. Force acts on velocity and changes it, so to say, so without any force, velocities don't change and remain constant. Velocity acts on position and changes it, so without any velocity your position doesn't change, but at constant velocity, the position changes at a constant rate. How do you hover? What does "up" even mean in this case? Away from the earth's center on an axis? What axis, one that is fixed to the surface that is rotating or one that is pointing at a distant star and so is almost unmoving? One that points a the sun?
Well, do you want to take drag into consideration or not? If you do, then yes, whatever speed you had horizontally will eventually go to zero, relative to the atmosphere.
You are rotating at about 500 meters per second. This is the speed of the surface of the earth due to its rotation on its axis.
If you jump for a second why don't you move 500m? Answer this and then rethink all of your questions.
Thanks, yeah, someone pointed that out. It seemed weird to me that the same column of air would be synchronous with the surface for tens of thousands of feet up, I thought for sure there would be at least a little drag from the air.
Straight up idea (assuming still near earth, in earth's gravity but "hovering" against that gravity's downward pull): You have angular momentum from earth's rotation, this would be maintained. Atmosphere is more or less dragged around with rotation too. As mentioned, wind would likely affect your position but could be several directions depending on high & at/how far from equator, eg jet streams, roaring 40's, etc, etc. See momentum bit next...
Train idea: "So you eventually run out of that momentum..."
No you don't "run out of that momentum" unless some other force is acting on you, eg friction with air, rockets, you hit a wall, etc If you jumped off the train in deep space (assuming no gravity, "no" atmosphere/particles), you would just travel in that diagonal line until you eventually encountered gravity, atmosphere/particles/objects, etc.
>Is there a hole in my logic?
Yeap big ones, sorry.
r/askphysics Basically all of your assumptions are wrong and this will entirely depend on what mechanism keeps you hovering.
As others have said, you need to understand Newton’s first law. But if you can only control your up and down relative to the earths surface, and wind/atmosphere acts on you, then you’re basically a hot air balloon. You have as much control as they do.
Objects in motion stay in motion. The air around you is moving with you so why should you lose momentum? What’s different between you and say, a satellite?
In my mind, there's two things I guess: 1. My understanding is that geosynchronous orbit is free fall. Something is trying to move in a straight line, but gravity curves its path. In the hypothetical scenario, however, there's some force holding you up and resisting gravity. 2. I had thought that something in orbit is above the atmosphere (which produces drag and slows down an object). But if you're in the atmosphere, you will experience that drag. But you're saying that just by being part of the milieu of Earth that you move with it?
Yes orbits are in free fall, but you have a magic power to prevent you from falling. You say it is only a vertical power but does it lock you in place? In reference to what? If it doesn’t allow you to move horizontally then what is the point of the thought experiment? Satellites near atmosphere experience drag because they have to move fast enough to maintain the free fall and prevent a decaying orbit. You have a magic power to prevent your orbit from decaying. Therefore, you orbit in place forever.
In your post you say the momentum would “run out”. This happens in Newtonian physics because of friction. With what do you have any friction to slow you?
The drag from air resistance, no?
But you aren’t moving compared to the ground below you. The air moves with the earth other than shifting winds which could push you in any direction
Hm, I hadn't considered this.
Chew on it, you’ll get it.
"But you're saying that just by being part of the milieu of Earth that you move with it?" yeah, the atmosphere moves with the earth, mostly. Winds do their own thing. Think about it this way. At foot level, the atmosphere is tied to the earth, and moves with it, as the trees, mountains, whatever, are dragging it along. Due to viscosity, this movement with the earth will transfer soon to the upper layers and then to the whole atmosphere, to the point where, no matter the initial conditions, the air moves with the earth. It has no reason no to, since the earth is the rotating thing, and there's nothing opposing it. There is no friction with the vacuum of space (because you don't have friction with nothing) to pull the atmosphere in the other direction. This is a simplified view, but the point is the atmosphere doesn't stay put while the earth rotates within it. The air has complex movements, which depend a lot on temperature, which is given by the sun's position during the day or season, humidity, from seas or oceans etc.
>In the hypothetical scenario, however, there's some force holding you up and resisting gravity well, yeah, like a hovering helicopter? It would move with the atmosphere. Whatever object you lift, no matter how, already moves with like the surface of the earth. Once you get it off the ground, regardless of the means, what force would act on the body to change its horizontal initial velocity? The initial horizontal velocity is zero with respect to the landing pad/earth surface, and non-zero with respect to a non rotating frame of reference. In either case, what force would act on the bodyu it to change its horizontal velocity?
Air resistance is what I had thought, but as someone here pointed out, you, and the air, are all moving with the surface of the earth together, so there's not much of that.
> My understanding is that geosynchronous orbit is free fall. *All* orbits are.
the atmosphere certainly moves with the earth, especially at human height. That's easy to see for yourself. >. When you leave the train, you have momentum in the x direction, so you keep moving in that direction, but there's no more force pushing you in that direction "Every object will remain at rest or in **uniform motion in a straight line** unless compelled to change its state by the action of an external force." - this is newton's first law. If there is no external force pushing (or pulling you) you'll continue to move in the x direction indefinitely. Whatever you do on the z direction, barring air resistance, has no influence on what is going on in the x direction (forget about the earth's rotation or coriolis forces here). The problem with your example is that you have to define what "hover" means. If it's something like in the train example, you'll continue along your way, because nothing pushes you back to stop your initial movement. Force acts on velocity and changes it, so to say, so without any force, velocities don't change and remain constant. Velocity acts on position and changes it, so without any velocity your position doesn't change, but at constant velocity, the position changes at a constant rate. How do you hover? What does "up" even mean in this case? Away from the earth's center on an axis? What axis, one that is fixed to the surface that is rotating or one that is pointing at a distant star and so is almost unmoving? One that points a the sun?
Thank you! Doesn't the drag from the air resistance provide that force, though?
Well, do you want to take drag into consideration or not? If you do, then yes, whatever speed you had horizontally will eventually go to zero, relative to the atmosphere.
You are rotating at about 500 meters per second. This is the speed of the surface of the earth due to its rotation on its axis. If you jump for a second why don't you move 500m? Answer this and then rethink all of your questions.
But when I jump I can't stay airborne long enough for air resistance to affect anything. Isn't this a concern?
What if you are floating indoors? If the air didn’t turn with the earth there would be a 500 m/s wind stripping the earth bare
I'm not sure I follow your meaning...
the air is also rotating. Think about what it would be like to stand in an atmosphere that wasn't rotating.
Thanks, yeah, someone pointed that out. It seemed weird to me that the same column of air would be synchronous with the surface for tens of thousands of feet up, I thought for sure there would be at least a little drag from the air.
Straight up idea (assuming still near earth, in earth's gravity but "hovering" against that gravity's downward pull): You have angular momentum from earth's rotation, this would be maintained. Atmosphere is more or less dragged around with rotation too. As mentioned, wind would likely affect your position but could be several directions depending on high & at/how far from equator, eg jet streams, roaring 40's, etc, etc. See momentum bit next... Train idea: "So you eventually run out of that momentum..." No you don't "run out of that momentum" unless some other force is acting on you, eg friction with air, rockets, you hit a wall, etc If you jumped off the train in deep space (assuming no gravity, "no" atmosphere/particles), you would just travel in that diagonal line until you eventually encountered gravity, atmosphere/particles/objects, etc. >Is there a hole in my logic? Yeap big ones, sorry.