What would happen if you throw a stone in outer space ?
Answers
The part about “no air resistance” is correct, but the part about “no gravity” is wrong. Gravity is everywhere in space. It’s what holds the Earth in its orbit and keeps our solar system within our galaxy. Gravity binds our galaxy with its nearby (in intergalactic terms) neighbor galaxies into what astronomers cleverly call the Local Group.
You didn’t say where you threw the stone from. If you threw it from the Earth’s surface, it can’t possibly make it into space — either gravity will stop it and pull it back to Earth, or the stone will burn up from friction and compression heating as it passes through the air.
If you were above the Earth’s atmosphere and threw the stone outward, whether or not it continues forever depends on its velocity. In order to escape Earth’s gravity, it has to be traveling at escape velocity, which for the Earth is 25,020 miles/hour (11.2 km/s). If the stone is traveling at less than escape velocity, the Earth’s gravity will eventually slow it, stop it, and pull it back down.
If you can throw the stone faster than Earth’s escape velocity, what happens next again depends again on how fast the stone is traveling. If it is traveling at less than 42 km/s, it will not be able to escape the sun’s gravity, and will enter an orbit around the sun. Faster than that, and it will escape into interstellar space.
If it manages to escape the solar system, then the answer is yes, it will continue forever, unless it hits something (extremely unlikely). Along the way, the gravity of nearby planets, stars, and other objects will alter its path, so it won’t necessarily continue in a straight line.