*If* the ISS is freely falling, doesn't that mean it's following

In summary, according to relativistic mechanics, the curvature in spacetime being created by Earth's gravity is what keeps the ISS orbiting around Earth. However, if the ISS were closer to the Earth's surface, it would need to speed up to maintain its orbit.
  • #1
49ers2013Champ
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...curvatures in spacetime being created by Earth's gravity?

My understanding is that its speed offsets the gravity being created by earth, that it's freely falling towards Earth but never hits it because its speed somehow causes it to keep missing. If that's the case, wouldn't that suggest that the ISS is under the influence of Earth's gravity (but that it just constantly maintains its orbit because of speed)?

Thanks.
 
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  • #2
doesn't that mean it's following...curvatures in spacetime being created by Earth's gravity?
As seen by general relativity: Right.
My understanding is that its speed offsets the gravity being created by earth
I don' think "offset" is the right word here.
that it's freely falling towards Earth but never hits it because its speed somehow causes it to keep missing.
That is better.
If that's the case, wouldn't that suggest that the ISS is under the influence of Earth's gravity (but that it just constantly maintains its orbit because of speed)?
Of course it is!
 
  • #3
49ers2013Champ said:
curvatures in spacetime being created by Earth's gravity?

I would say the curvature in spacetime *is* Earth's "gravity"; they aren't two separate things, one of which is created by the other. However, that's really a side issue here.

The more important point is that it's curvature in *spacetime*, not space. In spacetime, the path of the ISS is not an ellipse; it's a helix, because time is one of the dimensions. The Earth's path in spacetime is just a line that runs upward (assuming we think of the time direction as "upward") through the center of the helix.

49ers2013Champ said:
My understanding is that its speed offsets the gravity being created by earth, that it's freely falling towards Earth but never hits it because its speed somehow causes it to keep missing. If that's the case, wouldn't that suggest that the ISS is under the influence of Earth's gravity (but that it just constantly maintains its orbit because of speed)?

Since the Earth is the primary determinant of spacetime curvature in its vicinity, yes, the ISS's trajectory, given its speed at some particular instant, is primarily due to the Earth.
 
  • #4
Peter, I have a question related to this that may seem trivial but would help me understand this some more.

If the ISS were closer to the Earth's surface, would it have to speed up or slow down to maintain its smooth orbit around the earth?
 
  • #5
49ers2013Champ said:
If the ISS were closer to the Earth's surface, would it have to speed up or slow down to maintain its smooth orbit around the earth?

The orbital velocity gets larger as the radius gets smaller, so if the ISS were closer to the Earth, it would need to speed up to maintain orbit.
 
  • #6
You can answer that using Newtonian gravity. ##\frac{GM_{e}}{r^{2}} = \frac{v^{2}}{r}\Rightarrow v^{2} = \frac{GM_{e}}{r}## so smaller ##r## means larger ##v##.

EDIT: Peter won this one :frown:
 
  • #7
This reminds me of Olympic ski jumpers and how they can jump so far. :smile:
 

1. If the ISS is freely falling, what keeps it from crashing to the ground?

The ISS is constantly falling towards the Earth, but it is also moving at a high speed sideways. This sideways motion, known as its orbital velocity, keeps it from crashing to the ground and causes it to continuously fall around the Earth.

2. How does the ISS stay in orbit if it is falling?

The ISS stays in orbit by constantly falling towards the Earth while also moving at a high speed sideways. This combination of falling and moving sideways creates a curved path around the Earth, known as an orbit.

3. Does the ISS ever stop falling?

No, the ISS is always falling towards the Earth due to the force of gravity. However, its sideways motion keeps it from crashing to the ground and allows it to continuously fall in a circular path around the Earth.

4. Is the ISS considered weightless because it is falling?

Yes, the feeling of weightlessness experienced by astronauts on the ISS is due to the fact that they are constantly falling towards the Earth at the same rate as the ISS. This gives the illusion of weightlessness, but they are actually still being pulled towards the Earth by gravity.

5. Could the ISS ever fall out of orbit and crash to the ground?

Yes, the ISS could potentially fall out of orbit if it experiences a decrease in its orbital velocity or if it encounters an external force that affects its orbit. However, NASA closely monitors the ISS's orbit and makes adjustments to ensure that it stays in orbit and does not crash to the ground.

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