Full_Temperature_920 t1_j2dg30n wrote
Reply to comment by Gnonthgol in eli5: back then, before astronouts goes to space, how do we know about thing like nonexistent of oxygen & zero gravity? by zetasstra
Wait, so you're saying things in orbit are just endlessly falling? Does that apply to the earth and the sun as well? Is the earth's orbit just the earth falling towards the sun but missing? That's fascinating lol. Oh shit does this mean the moon is always falling towards the earth??
cavalier78 t1_j2dhb8v wrote
Yes. But everything is also moving fast perpendicular to the falling direction. Like it’s falling down, but it’s also going thataway so fast that it always misses the Earth. And there’s no air in space to slow you down, so you just keep going thataway and keep missing the Earth.
SomethingMoreToSay t1_j2di49z wrote
>Wait, so you're saying things in orbit are just endlessly falling?
That's exactly right.
Fun fact: If you want to go into space, the key problem isn't going high enough, it's going fast enough. If you don't go fast enough, you'll fall down and hit the earth. But if you go fast enough, you'll miss the earth and you'll be in orbit.
svidale t1_j2dhjfq wrote
Yes, calculated to get just the right angle and speed to be missing. I don't think thats endless though. As in, most satellites will eventually crash down anyway. Even the international space station has to fire up its boosters sometimes to stay in the right orbit angle.
Scuka1 t1_j2e3ktu wrote
>I don't think thats endless though
It is endless in theory, if you're high enough.
ISS has to boost because, even though it's technically outside the atmosphere, there are still some air particles floating around up there, producing a tiny amount of drag which needs to be compensated every so often.
For a body to stay in orbit, it needs to have a certain speed. Drag is slowly taking that speed away. Boosting is adding that speed back.
Full_Temperature_920 t1_j2e7j76 wrote
I'm assuming planets and other celestial bodies don't experience drag in space, so those definitely will keep orbiting their star until it expands and swallow them then? Assuming nothing flying through space impacts them with enough momentum to shift the course
Scuka1 t1_j2e9lzb wrote
Well, in theory, if conditions don't change, an orbit remains unchanged forever.
However, in practice, in our Solar system for example, you've got planets orbiting the Sun, each at their own pace, and every planet is exerting some gravitational force on other planets as they pass each other by, making tiny changes in their orbits.
So, orbits do change over HUGE periods of time (but we're talking slight changes over millions of years), but they don't really decay.
ViciousKnids t1_j2drffz wrote
Yes and Issac Newton was the one to make a mental picture of the relationship of speed, trajectory, and gravity called "Newton's Cannonball." He hypothesized that there's basically a "sweet spot" in which an object traveling fast enough to not fall back to a surface but slow enough to not trail off into space. He hypothesized that gravity was a universal force and was the driver of planetary and satellite motion.
It's a pretty famous though experiment. It's even referenced in Issac Newton's episode of Epic Rap Battles of history.
Scuka1 t1_j2e37sv wrote
Yes. Orbit is basically a fall that "misses" the Earth (or whatever body you're orbiting around).
Newton's Cannon is a great explanation of that.
https://i.stack.imgur.com/STNEW.jpg
If you launch an object, it will fall in a curved path. If you launch if faster, it will fall in a curved path, but with a larger radius. If you launch it REALLY fast, the radius of that curve will be such that it will go around the Earth.
That's how rockets reach orbit. They basically accelerate sideways a lot.
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