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How do things in space end up pulled into each other? If big object A pulls small object B with gravity, wouldn't B just speed up and then miss, ending up in s

How do things in space end up pulled into each other? If big object A pulls small object B with gravity, wouldn't B just speed up and then miss, ending up in some kind of orbit? Like, if you are in space and throw a rock at the Sun, it won't hit unless you perfectly counteract the relative speed, right?

laserlight 4y ago
That's right, as explained in the following minutephysics video (3 minutes): Hitting the Sun is HARD. https://www.youtube.com/watch?v=LHvR1fRTW8g https://www.youtube.com/watch?v=LHvR1fRTW8g
lisper 4y ago
You can tell that there must be something wrong with your reasoning by observing that meteorites regularly impact earth. You are correct that it is not easy to make things collide in space. But it's (obviously) not impossible. The trajectory doesn't have to be perfect, just close enough that the lowest point in the orbit is less than the radius of the object being orbited. In the case of a supermassive black hole, that's a pretty big target. The event horizon of Sgr A* is about 50 million kilometers in diameter, and that is surrounded by an accretion disk that acts kind of like an atmosphere, so anything that comes close gets slowed down through friction, and then it eventually falls in. (Also, near black holes, general relativity makes things kinda weird.) > if you are in space and throw a rock at the Sun, it won't hit unless you perfectly counteract the relative speed, right? If you are out in space in orbit around the sun this is true. But there are lots of ways to be "out in space" not in orbit around the sun. The reason that most of the stuff we see is in orbit around the sun is that the stuff that is not in orbit around the sun doesn't stick around very long. It either flies off into deep space, or it falls into the sun.
- darkerside 4y ago
  Hmm, the meteorite never reaches the core of the Earth. It just happens to explode on contact with the massive crust that's constantly rotating around it. Similarly, that rock would be pulverized by the heat of the Sun before it ever came to a rest at its center. Assuming of course that you could "throw" that rock hard enough to counter our massive rotational velocity.
dotnet00 4y ago
It'd speed up and miss, but say it passes through a cloud of gas which acts as drag and slows it down a little, now it misses the body slightly less, keep this going for a few thousand years and its lost enough energy relative to the first body that it can't keep 'missing' anymore and collides/falls in. They're essentially counteracting that relative speed over time by bleeding energy to all sorts of drag (one exotic example that comes to mind is with things like neutron stars and black holes bleeding out vast amounts of energy in gravitational waves - literal waves in space-time we can detect from billions of light years away - in the moments before they crash into each other).

laserlight 4y ago

That's right, as explained in the following minutephysics video (3 minutes): Hitting the Sun is HARD. https://www.youtube.com/watch?v=LHvR1fRTW8g https://www.youtube.com/watch?v=LHvR1fRTW8g

lisper 4y ago

You can tell that there must be something wrong with your reasoning by observing that meteorites regularly impact earth. You are correct that it is not easy to make things collide in space. But it's (obviously) not impossible. The trajectory doesn't have to be perfect, just close enough that the lowest point in the orbit is less than the radius of the object being orbited. In the case of a supermassive black hole, that's a pretty big target. The event horizon of Sgr A* is about 50 million kilometers in diameter, and that is surrounded by an accretion disk that acts kind of like an atmosphere, so anything that comes close gets slowed down through friction, and then it eventually falls in. (Also, near black holes, general relativity makes things kinda weird.) > if you are in space and throw a rock at the Sun, it won't hit unless you perfectly counteract the relative speed, right? If you are out in space in orbit around the sun this is true. But there are lots of ways to be "out in space" not in orbit around the sun. The reason that most of the stuff we see is in orbit around the sun is that the stuff that is not in orbit around the sun doesn't stick around very long. It either flies off into deep space, or it falls into the sun.

darkerside 4y ago
Hmm, the meteorite never reaches the core of the Earth. It just happens to explode on contact with the massive crust that's constantly rotating around it. Similarly, that rock would be pulverized by the heat of the Sun before it ever came to a rest at its center. Assuming of course that you could "throw" that rock hard enough to counter our massive rotational velocity.

dotnet00 4y ago

It'd speed up and miss, but say it passes through a cloud of gas which acts as drag and slows it down a little, now it misses the body slightly less, keep this going for a few thousand years and its lost enough energy relative to the first body that it can't keep 'missing' anymore and collides/falls in. They're essentially counteracting that relative speed over time by bleeding energy to all sorts of drag (one exotic example that comes to mind is with things like neutron stars and black holes bleeding out vast amounts of energy in gravitational waves - literal waves in space-time we can detect from billions of light years away - in the moments before they crash into each other).