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Deepak K Kapur
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When astronauts go into space (considerably away from Earth) they feel weightlessness. They just move aimlessly in space.
Why doesn't moon move aimlessly in space?
Why doesn't moon move aimlessly in space?
Funded by our tax money!Deepak K Kapur said:They just move aimlessly in space.
arildno said:You are somewhat confused about "the experience of weightlessness", relative to how we should say whether a person is subject to the force of gravity, or not.
Now, first off:
If we look into general relativity, the conception of "force", in particular gravity, is radically different from that within classical mechanics, but YOUR confusion can as easily be explained in terms of classical mechanics, so that is what I'll do:
When we "feel" our own weight, what is the ACTUAL force we are sensing?
If you simply stand on the ground, it is the NORMAL FORCE acting from the ground on you experience, that you think of as your "weight" (it is oppositely directed to gravity, but of the same magnitude).
Note that if you are in an elevator accelerating upwards, you will FEEL heavier (you feel a stronger push on your feet), although gravity hasn't changed a bit, but the normal force acting upon you has increased.
Are you in FREE FALL, only gravity acting on you, you will feel weightless.
Astronauts and the moon is in FREE FALL around the Earth (the moon keeps missing its target, fortunately!)
But, free fall is a situation in which you, as emphasized are under the influence of gravity, which in the classical mechanics point of view means you are subject to an external force, making your motion deviate from that of following a straight line of motion. You are following a determinate orbit, not floating "aimlessly" around.
As long as they don't push away they'll stay in the same orbit as the station indefinitely. If they do push away or otherwise apply force to themselves(e.g., with rockets) they'll change orbit to a different one, which will most likely take them farther and farther from the station.Deepak K Kapur said:So, why the astronauts who are to repair the space station tied with a rope to the space station?
If they are not tied, they would just drift away and may even reach the those regions of deep space from where they may never return back to earth. Isn't it so?
Deepak K Kapur said:So, why the astronauts who are to repair the space station tied with a rope to the space station?
If they are not tied, they would just drift away and may even reach the those regions of deep space from where they may never return back to earth. Isn't it so?
Deepak K Kapur said:So, why the astronauts who are to repair the space station tied with a rope to the space station?
If they are not tied, they would just drift away and may even reach the those regions of deep space from where they may never return back to earth. Isn't it so?
Well, why not? The rest of government moves aimlessly!A.T. said:Funded by our tax money!
One reason astronauts are tethered is that the astronaut and space station are *not* in the same orbit. Very similar orbits, yes. The same orbit? No.Bandersnatch said:As long as they don't push away they'll stay in the same orbit as the station indefinitely.
No. The gravitational force exerted by a 2 meter diameter iron ball on an astronaut 2 meters from the center of the ball is tiny, much smaller than the gravitational tidal force exerted by the Earth that acts to pull the astronaut away from the ball. For more info, google the term "Hill sphere."Deepak K Kapur said:Does all this mean:
1. The astronaut will be able to walk on an iron ball say 2 metre wide in all the directions (assuming astronaut and a ball only are in orbit).
A qualified yes. In a sense, the spaceship is *always* orbiting the Sun. You are implicitly treating "orbit" as a mutually exclusive term. For example, does the Moon orbit the Earth or the Sun? The answer is "yes". The Moon orbits both the Earth *and* the Sun.2. If you take the spaceship to a place between Venus and Earth where the effect of gravitation of both the planets is nil (or negligible), would the spaceship start orbiting the sun?
Another qualified yes. I'm not a fan of these kinds of questions. We don't live in a universe in which there is nothing but the Earth and the spaceship. However, the answer is yes with the assumption that the laws of physics in this nearly empty universe are the same as the laws of physics in our universe filled with lots of stuff. The spaceship needs to be moving at a ridiculously slow speed, however. Escape velocity at a million light years is 2.9×10-4 meters per second.3. Assuming there is nothing else in the universe except our Earth, would a spaceship orbit the Earth even if the spaceship is, say, a million light years away?
Not really. Atmospheric density falls off more or less exponentially, and the Moon is fairly massive. Atmospheric drag on geosynchronous satellites is tiny, tiny, tiny, and by the time you get to the Moon, the Earth's atmosphere is pretty much non-existent.4. Does the moon also experience friction?
arildno said:Note that in free space, the TINIEST collision type between astronaut and the ship will generate oppositely directed momenta (measured relative to the frame in which they gain the same velocity from the Earth).
D H said:The Hill sphere of the ISS is about 5.5 meters in diameter. So no.
Deepak K Kapur said:If this is true (at least in principle), why do we need an escape velocity of 11.2 km/s.
QED, in a very illustrative way!Vanadium 50 said:A friend of mine lost her toolkit in orbit when a grease gun didn't shut off properly. Propelled it like a rocket. A very slow rocket, but a rocket nonetheless. It wasn't until the following year until the toolkit reentered.
D H said:Another qualified yes. I'm not a fan of these kinds of questions. We don't live in a universe in which there is nothing but the Earth and the spaceship. However, the answer is yes with the assumption that the laws of physics in this nearly empty universe are the same as the laws of physics in our universe filled with lots of stuff. The spaceship needs to be moving at a ridiculously slow speed, however. Escape velocity at a million light years is 2.9×10-4 meters per second.
Stopping the engines doesn’t necessarily make it move towards Earth immediately. Especially if it was already moving faster than escape velocity at that distance.Deepak K Kapur said:Suppose the spaceship (that is a million light years away from Earth) stops firing its rockets. It will start moving towards earth.
A million years.Deepak K Kapur said:When would Earth know (detect, come into picture) about this?
Vanadium 50 said:A friend of mine lost her toolkit in orbit when a grease gun didn't shut off properly. Propelled it like a rocket. A very slow rocket, but a rocket nonetheless. It wasn't until the following year until the toolkit reentered.
Deepak K Kapur said:When would Earth know (detect, come into picture) about this? Instantaneously or after a million years?
georgir said:The fun part is, it doesn't matter. The Earth would be approximately equally attracted toward the spaceship and its fuel, no matter if they both fall toward the Earth together, or they split up, fuel hurling towards Earth so that the ship can move further away...
And if "approximately" is not good enough for you, the answer would depend on who you ask...
Newton would say the Earth instantly knows how to react. Einstein would say the Earth instantly reacts as if it assumed the fuel/rocket fell gravitationally, and if they didn't, the information about that would spread at light speed...
Your intuition is wrong. That's not how it works.Deepak K Kapur said:Let us divide the space between the very-very distant satellite and Earth into small parts, say 1 light second apart, each.
Unless each part of space communicates with each other part simultaneously, the effect of gravitation cannot take place. This communication, to my mind, has to be instantaneous.
Objects fall to the ground because of the force of gravity. Gravity is a force that exists between any two objects with mass and pulls them towards each other. The larger the mass of an object, the stronger its gravitational pull.
Gravity works by the principle of mass attracting mass. The more mass an object has, the more gravitational pull it exerts on other objects. Gravity also follows the law of universal gravitation, which states that the force of gravity between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
We stay on the ground because the Earth has a much larger mass than our bodies, so its gravitational pull on us is much stronger. This force of gravity keeps us grounded and prevents us from floating away into space.
Yes, gravity works the same everywhere in the universe. However, the strength of gravity can vary depending on the mass of the objects and the distance between them. For example, the force of gravity on the moon is weaker than on Earth because the moon has less mass.
No, gravity cannot be turned off. It is a fundamental force of nature that exists everywhere and cannot be controlled or manipulated by humans. However, astronauts in space experience weightlessness because they are in a state of freefall around the Earth, but gravity is still present and keeping them in orbit.