I kind of understand that it’s like falling but falling past Earth but not really. Does it require power (in the case of artificial satellites, obviously the moon doesn’t have power) or does orbit last basically forever. If two things in orbit collide will they fall? If Deimos and Phobos somehow crash into each other will they just fall to Mars?
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When you throw a ball or fire a bullet, gravity pulls it down in an arc or curve shape. You know what also has a curve? The earths surface. What if the 2 shapes were the same size, so that the falling object always fell down at the same rate that the curvature of the Earth fell away from it? Voila, you’re in orbit now. You’ll keep falling forever and never get any closer to the ground. If you do something to slow the object down, however, then those shapes wont match any more and you WILL get closer to the ground, likely hitting it. In theory you don’t need any power to maintain orbit, but in reality for things in low earth orbit there are very very minor amounts of molecules that will slowly bleed you of your speed if you are close to the atmosphere. If you are far enough away then the drag will be negligible and you will stay up there indefinitely.
Imagine you are skydiving over lava (ignoring air resistance). If you fall without any horizontal speed, you’ll hit the lava every time. But if I push you, you’ll miss. If I push you harder, you’ll miss more. If the lava pool gets bigger, I keep having to push harder and harder to save you.
Eventually if the lava covers all the Earth, I have to push you so hard that you loop all the way back to where you started. That’s orbit.
Note: I didn’t need to add any speed after the initial push, so when you ignore air resistance, orbit doesn’t need power.
But in reality, air does exist, and it slows down our satellites, meaning they do need power, but it’s not a lot.
As for Phobos and Deimos, it depends on *how* they hit each other. A head on collision would make them lose orbit, but it all depends on how fast they’re going after the collision.
You’re falling down, but you’re just moving sideways fast enough that you miss the planet, it’s curving away from you as fast as you’re accelerating towards it. Imagine shooting a bullet perfectly sideways with no air, gravity pulls it down, but the curvature of the earth gives it extra height. Go fast enough and the planet can’t pull you down fast enough to make you hit the ground.
Orbits don’t last forever, if nothing else the gravitational waves will sap the energy required to maintain it. However that’s not going to happen on timescales we need to worry about. The moon is also gaining orbital energy from tidal forces, slowing Earth’s spin in the process.
What does matter for low orbits is the atmosphere. There’s not really a hard cutoff point where there’s no more atmosphere. Stuff in lower orbits will hit enough air molecules to deorbit in a few years. Stuff out at geostationary orbit will be there for a VERY long time.
If two objects collide they may or may not stay in orbit, it depends on what their velocity ends up after the collision. If they’re moving in the same direction around the planet, the objects or debris can stay in orbit. if they’re moving in opposite directions there’s a good chance the bulk of the objects won’t have enough energy to stay in orbit, though some fragments might.
Imagine standing on the top of a skyscraper, if You walk off its edge, You’re gonna fall, no surprize. Now if You measure from the bottom of the skyscraper to the point at which You landed, it’s a certain distance away from the bottom of the skyscraper since You maintained the walking speed through the fall. Now if You were to run off of the top edge of the skyscraper, You’d fall again, but land further away from the skyscraper, again, since You maintained the speed at which You left the skyscraper. If You were to run off of the top edge of that skyscraper fast enough, You’d not land at all, but You’d keep falling. The curvature of the earth would curve away from You all the while You’re falling, this would go on sand on and on if it wasn’t for atmospheric drag slowing You down.
Orbit is functionally a perpetual freefall.
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