Hi - Thanks for the link to your blog. I thought we should probably move this fascinating discussion here, since it's a more appropriate place for it.
I'm still trying to understand how the GEO satellite "stays put". Let me try to explain what confuses me.
First, let's stop the universe from rotating (!). The satellite sees two forces, one force vector points from the satellite though the center of the Earth (that's gravity). If we want the satellite to stay put, that force must be balanced by an equal and opposite force (from the universe's collective gravity). So far, so good.
Now, let's let the universe rotate again (phew!). That force vector that was counteracting gravity will follow whatever part of the universe was exerting it, dragging the satellite with it. Right?
But if all parts of the universe exert an (almost) equal gravitational force, we have another problem. The gravitational force from the part of the universe "behind" the Earth is the same as the force from the part of the universe "above" the satellite. Think of the earth as the center of a plate, the satellite is a pea on the edge of the plate, draw a line on the plate, from the satellite, through the earth, to the other side of the plate - there's a force coming from there' too, right?)) So wouldn't these two force vectors cancel each other out (because they're equal and opposite)?
Physics class, with all those force vectors was a long time ago, so maybe I have missed something?
Hi -
ReplyDeleteThanks for the link to your blog. I thought we should probably move this fascinating discussion here, since it's a more appropriate place for it.
I'm still trying to understand how the GEO satellite "stays put". Let me try to explain what confuses me.
First, let's stop the universe from rotating (!). The satellite sees two forces, one force vector points from the satellite though the center of the Earth (that's gravity). If we want the satellite to stay put, that force must be balanced by an equal and opposite force (from the universe's collective gravity). So far, so good.
Now, let's let the universe rotate again (phew!). That force vector that was counteracting gravity will follow whatever part of the universe was exerting it, dragging the satellite with it. Right?
But if all parts of the universe exert an (almost) equal gravitational force, we have another problem. The gravitational force from the part of the universe "behind" the Earth is the same as the force from the part of the universe "above" the satellite. Think of the earth as the center of a plate, the satellite is a pea on the edge of the plate, draw a line on the plate, from the satellite, through the earth, to the other side of the plate - there's a force coming from there' too, right?)) So wouldn't these two force vectors cancel each other out (because they're equal and opposite)?
Physics class, with all those force vectors was a long time ago, so maybe I have missed something?