For a body to stay in orbit around Earth, it must travel tangentially (magenta arrow) with a velocity that lets the body fall a radial distance due to the force of gravity (black arrow) in such a way that it follows the curvature of Earth (yellow arrow). The resultant displacement can be represented as the sum of both motions (blue arrow).
I browsed over this the other day but it didn't mean anything to poor old me.
Then yesterday it came to me. I understood.
Imagine a pole in your back garden with a wire attached to a ball that could freely spin 360. You can then throw the ball with sufficient force that it comes back to you, it does one orbit.
This is very crude, please excuse.
is the direction of force, very important. Now imagine the direction of force at every point the ball will take on it's journey. The little man is at each station and f
is going off at a tangent.(See image 2 above) His mirror image will be at 12:00, with f
pointing in the opposite direction.
If I launch the ball gently it will not make one orbit but collapse, if I launch it hard, it orbits, decays quickly then collapses.
To keep the ball constantly spinning around the pole, constant force along f
needs to be applied, or it's orbit will decay rapidly?
Where does the constant force f
come from that make objects like the "ISS" travel tangentially
with sufficient velocity that it remains in orbit?