3 ms·

Okay, but what if you were on the Moon? Would the absence of atmospheric friction result in a different outcome? Also, I've heard you could fire a bullet on the

Okay, but what if you were on the Moon? Would the absence of atmospheric friction result in a different outcome? Also, I've heard you could fire a bullet on the Moon and it would be able to go into as low an orbit as a few 100 meters without ever hitting the ground. What's the minimal velocity for that to be plausible?

d_tr 4y ago
> What's the minimal velocity for that to be plausible? The escape velocity, which is 2.4 km/s on the surface of the moon, so you would need a pretty powerful gun :p
- perilunar 4y ago
  Low lunar orbit is a bit less than that, ~1.7 km/s. Higher than a rifle round, but a "kinetic energy penetrator" from a tank gun gets that fast [0] Many years ago I read a short story about a gun battle on the moon where the bullets orbit the moon. Took me an hour to find it: Men of Good Will by Ben Bova & Myron R. Lewis Galaxy v22n05 (June 1964), p 170. [1] 0. https://en.wikipedia.org/wiki/Muzzle_velocity https://en.wikipedia.org/wiki/Muzzle_velocity 1. https://archive.org/details/Galaxy_v22n05_1964-06_modified/page/n111/mode/2up https://archive.org/details/Galaxy_v22n05_1964-06_modified/p...
kadoban 4y ago
> Would the absence of atmospheric friction result in a different outcome? Yes. > Also, I've heard you could fire a bullet on the Moon and it would be able to go into as low an orbit as a few 100 meters without ever hitting the ground. What's the minimal velocity for that to be plausible? Apparently: 1679 m/s per https://www.quora.com/How-fast-must-an-object-be-moving-to-orbit-the-moon-at-elevation-of-say-1-2-miles-above-surface https://www.quora.com/How-fast-must-an-object-be-moving-to-o... . The answer isn't very sensitive to height because the radius in the equation is from the center of the moon, so the answer will only change a tiny amount. Note that low orbits on the Moon aren't stable. The Moon's gravity is lumpy due to its composition, so things that are low quickly become unstable and crash.

d_tr 4y ago

> What's the minimal velocity for that to be plausible? The escape velocity, which is 2.4 km/s on the surface of the moon, so you would need a pretty powerful gun :p

perilunar 4y ago
Low lunar orbit is a bit less than that, ~1.7 km/s. Higher than a rifle round, but a "kinetic energy penetrator" from a tank gun gets that fast [0] Many years ago I read a short story about a gun battle on the moon where the bullets orbit the moon. Took me an hour to find it: Men of Good Will by Ben Bova & Myron R. Lewis Galaxy v22n05 (June 1964), p 170. [1] 0. https://en.wikipedia.org/wiki/Muzzle_velocity https://en.wikipedia.org/wiki/Muzzle_velocity 1. https://archive.org/details/Galaxy_v22n05_1964-06_modified/page/n111/mode/2up https://archive.org/details/Galaxy_v22n05_1964-06_modified/p...

kadoban 4y ago

> Would the absence of atmospheric friction result in a different outcome? Yes. > Also, I've heard you could fire a bullet on the Moon and it would be able to go into as low an orbit as a few 100 meters without ever hitting the ground. What's the minimal velocity for that to be plausible? Apparently: 1679 m/s per https://www.quora.com/How-fast-must-an-object-be-moving-to-orbit-the-moon-at-elevation-of-say-1-2-miles-above-surface https://www.quora.com/How-fast-must-an-object-be-moving-to-o... . The answer isn't very sensitive to height because the radius in the equation is from the center of the moon, so the answer will only change a tiny amount. Note that low orbits on the Moon aren't stable. The Moon's gravity is lumpy due to its composition, so things that are low quickly become unstable and crash.