eli5: I’ve heard orbit described as continuously falling past or missing the Earth, how then do objects in geosynchronous orbit above a single point not fall out of the sky?

Question

eli5: I’ve heard orbit described as continuously falling past or missing the Earth, how then do objects in geosynchronous orbit above a single point not fall out of the sky?

In: 2204

Answer 1

It’s a kinda shitty description of what’s happening, but has a popular foothold for some reason.

A stable orbit is when the centripetal force to keep you moving in a circle is equal to the gravitational force at the same altitude. It’s about balancing forces, not about throwing yourself at the ground and missing.

Geosynchronous orbits are achieved by calculating what altitude has an orbital period equal to the rate of earth’s rotation, then you stick a satellite at that altitude, at the appropriate velocity.

Edit: For those who think this *isn’t* about balancing forces please share a non-force based derivation of how you calculate orbital velocity at a given altitude.

For reference the force-based derivation is:

GM(earth) /2 = V^2 /r
The left side is gravitational force at a given altitude
The right side is centripetal force required for a velocity at that altitude
This rearranges to
V = sqrt (GM(earth) / r)