Question about gravitational field

[joecap]

Greetings, fellow earthlings.

My apolgies for what is about to be a long post, but I have been curious about
a number of things for a while, and have not gotten any answers at any of the
astronomy sites I have been to:

I know that an object in geosynchronous orbit effectively "hovers" over a specific
point on earth, due to it actually orbiting the planet at the same relative speed as the
earth is revolving.

Yet the object does not actually "fall". So how high up does an object need to be
before it can do this without "falling"?
Also, what would be the minimum speed an object can be moving before it falls,
probably dependant on its altitude.

Also, I have heard that the force of the earth's gravity does not actually diminish very much
even at an altitude of several hundred miles. So, theoretically, if you can "hold" a spacecraft motionless
over the earth with no orbiting movement at all, "holding" it so it does not fall down, if you were standing
inside it, would you feel normal earth gravity? Would it just be a little less?

I know the feeling of no gravity aboard a spacecraft is actually just an illusion caused by centrifugal force
putting you into freefall around the planet.

Hopefully someone with more physics knowledge than myself will stumble upon this and answer.

Thanks! Joe Cap

[nbrosch]

Joe:

Greetings, fellow earthlings.

My apolgies for what is about to be a long post, but I have been curious about
a number of things for a while, and have not gotten any answers at any of the
astronomy sites I have been to:

I know that an object in geosynchronous orbit effectively "hovers" over a specific
point on earth, due to it actually orbiting the planet at the same relative speed as the
earth is revolving.

Yet the object does not actually "fall". So how high up does an object need to be
before it can do this without "falling"?

NB: The object does indeed fall, but because it has transversal velocity, it does miss the Earth all the time. This is why a satellite actually turns around the Earth.

Also, what would be the minimum speed an object can be moving before it falls,
probably dependant on its altitude.

About 7 km/sec.

Also, I have heard that the force of the earth's gravity does not actually diminish very much
even at an altitude of several hundred miles. So, theoretically, if you can "hold" a spacecraft motionless
over the earth with no orbiting movement at all, "holding" it so it does not fall down, if you were standing
inside it, would you feel normal earth gravity? Would it just be a little less?

The gravity would be a bit less, but it would be there. It would cause your soles to press on the lower deck of the spacecraft.

I know the feeling of no gravity aboard a spacecraft is actually just an illusion caused by centrifugal force
putting you into freefall around the planet.

Not really. A person in orbit is actually in free fall, as one would be in a freely falling elevator. As I explained above, the transversal velocity makes the spacecraft miss the Earth.

Hopefully someone with more physics knowledge than myself will stumble upon this and answer.

Thanks! Joe Cap

Hope this helps,
Noah Brosch