Planetary orbit: What makes any objects go in an orbit around the sun or the Earth?
Objects in orbit are really just falling. Consider what happens if you throw a rock horizontally on the Earth. It falls to the ground. But not where you are standing — because it’s moving horizontally, it falls some distance away from you. The harder you throw it, the further away it gets. But the Earth is curved. So there must be some speed at which you can throw the rock so that, by the time it falls to where the ground would’ve been (were the Earth flat), it isn’t there any more. Not only that, but the gravity isn’t pointing in the same direction any more, so the gravity is actually pulling behind a little bit as well as perpendicular to the rock’s flight — except that the rock’s flight has now curved due to the gravity acting on it. The speed it needs to be moving in order to stay at an even height above the surface is about 8 km/s or around 17,500 mph. That’s called “circular orbital velocity”. If it’s going faster, then it will rise up to a high-point (apogee) and fall back to
