How do we know geosynchronous sattelites are actually moving?

geocentrism went out a long time ago - as for your question, the earth rotates once a day and the sattelites manage to stay above one point on the spinning earth, so they must be revolving about the earth at the same speed as earth's rotation speed. Or look at it another way, if they were not in orbital motion, they would fall to the earth (gravity)

Well velocities are all relative, so in a sense if you take the earth to be the center of the universe (or in other words your reference frame) then they aren't moving. Really the only way to prove that the earth isn't the center of the universe is to prove something else is. We can take this to be the sun, but our sun moves in relation to other galaxies as well. It makes much more sense for us to model our solar system with the sun in the center since then orbital mechanics make much more sense, but it is completely possible to develop a path showing the sun orbiting the earth, however it wouldn't be a nice elliptical and definitely wouldn't be as easy to mathematically model as modelling the earth orbiting the sun. In short whether the satellites are moving is completely dependent on your reference frame, so if you take that to be the earth then they aren't.

Ask your friend how he/she'd keep a bucket of bolts hanging up without it falling down.
(On a side note, remember that Earth's gravity doesn't "disappear" when you're in space, otherwise the International Space Station would fly in a straight line away from Earth and never come back.)


<QUOTE>in an argument with someone who believes in geocentrism </QUOTE>

Doesn't matter. Personal beliefs do not dictate reality.

Do either of you have satellite TV or know someone who does?

Also, you can (with surprisingly modest equipment) can photograph these satellites.
http://www.youngsphotogallery.com/Img_0780x.jpg
http://www.universetoday.com/34623/geosynchronous-orbit/

if you're arguing with someone who really, truly, believes in geocentrism, then you're wasting your time.

we know they move because the rockets that put them up don't go straight up.
They go at an angle around the earth.

it's actually quite interesting.
geocentric satellites move slower in their orbits, but it takes more energy to put them there than it does low earth orbit satellites, which move around 18,000 mph.

geocentric satellites only move around 27000*2*pi/24 = 7,068 mph.

rather than wasting your time, you might consider how 2 moons can have the same orbit. Really.

http://en.wikipedia.org/wiki/Epimetheus_%28moon%29

If they didn't move, they wouldn't stay over one place on the Earth, since the surface of the Earth is moving (the Earth rotates).

I would love to hear how you use geosynchronous satellites to disprove geocentrism (the only relationship between the 2 is the term "geo" meaning "of the Earth").

Geosynchronous means that the sattelites stays over the same point on the earth and the earth is revolving around it's axis so the sattelites there for are moving. If your friend believes in a geocentric universe then they need to go back to school