# How fast does a bullet travel on the moon? **URL:** \ **Category:** Factual Questions\ **Created:** [September 2, 2004, 10:19pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849 "2004-09-02T22:19:06Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![minor7flat5](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/minor7flat5/32/258_2.png) [@minor7flat5](https://boards.straightdope.com/u/minor7flat5)\ **Post date:** [September 3, 2004, 2:05am UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/21 "2004-09-03T02:05:12Z")
Hmmmm… It looks like the Moon’s intrinsic escape velocity is [2.37 km/sec](http://home.tiac.net/~cri/1999/moon.html), but all of the high muzzle velocities I can find in a few moments of searching are in the neighborhood of 1km/sec. Contrary to my gut instinct (that wimpy Moon gravity would allow a rifle to launch a bullet off the moon), it seems that an ordinary rifle won’t pack the required punch. Of course, since the difference is not an order of magnitude, it’s quite imaginable that one could possibly create a special rifle that could do the job. I know nothing of the subtlties of escape velocity, though – does a launch at the equator at the right angle ever reduce the escape velocity _below_ the stated value? ---
**Author:** ![Bytegeist](https://avatars.discourse-cdn.com/v4/letter/b/9dc877/32.png) [@Bytegeist](https://boards.straightdope.com/u/Bytegeist)\ **Post date:** [September 3, 2004, 4:21am UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/22 "2004-09-03T04:21:20Z")
> [@minor7flat5](#): > > I know nothing of the subtlties of escape velocity, though – does a launch at the equator at the right angle ever reduce the escape velocity _below_ the stated value? Escape velocity will be very slightly less at the equator, because your distance from the Moon’s center is a tiny bit larger than at the poles. The Moon isn’t very oblate though, so that’s a little difference that makes little difference. Incidentally, the Moon does rotate a bit (in absolute terms, though not relative to the Earth), so if you’re near the equator, you’ll get a tiny velocity boost when firing in the eastward direction. This doesn’t change the escape velocity in the Moon’s “inertial” (non-rotating) coordinate system, but it does reduce the velocity you need to achieve relative to the ground. ---
**Author:** ![Dancer\_Flight](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dancer_flight/32/7601_2.png) [@Dancer\_Flight](https://boards.straightdope.com/u/Dancer_Flight)\ **Post date:** [September 3, 2004, 4:57am UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/23 "2004-09-03T04:57:31Z")
If you are going to actually perform this experiment, make sure the gun is well lubricated as is the cartridge and bullet to avoid [cold-welding](http://encyclopedia.thefreedictionary.com/Cold%20welding). In a high vacuum, extremely clean surfaces (no oxide layer) tend to stick together rather permanently especially when subjected to heat and mechanical pressure. Note that it appears that unintentional cold-welding has thus far not been a major problem during space missions but I thought I’d show off my surface chemistry class :). -DF ---
**Author:** ![SPOOFE](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@SPOOFE](https://boards.straightdope.com/u/SPOOFE)\ **Post date:** [September 3, 2004, 7:48am UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/24 "2004-09-03T07:48:17Z")
> [@](#): > > It looks like the Moon’s intrinsic escape velocity is 2.37 km/sec, but all of the high muzzle velocities I can find in a few moments of searching are in the neighborhood of 1km/sec. [Here’s a gun](http://www.stormingmedia.us/23/2308/A230891.html) that’ll do the job… “This gun should be capable of launching a… 160 gram saboted KE penetrator at **3 km/sec** ” (bolding mine). 😃 ---
**Author:** ![Rufus\_Xavier](https://avatars.discourse-cdn.com/v4/letter/r/eada6e/32.png) [@Rufus\_Xavier](https://boards.straightdope.com/u/Rufus_Xavier)\ **Post date:** [September 3, 2004, 12:58pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/25 "2004-09-03T12:58:51Z")
Okay…assuming a rifle was located that could launch a bullet into space from the moon, and the trajectory was calculated so that the bullet would hit land (say, in my backyard, for the heckuvit), would the bullet survive the trip and embed itself in the ground, or would it be burned up in Earth’s atmosphere? ---
**Author:** ![paulberserker](https://avatars.discourse-cdn.com/v4/letter/p/c4cdca/32.png) [@paulberserker](https://boards.straightdope.com/u/paulberserker)\ **Post date:** [September 3, 2004, 1:05pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/26 "2004-09-03T13:05:38Z")
[This thread](http://boards.straightdope.com/sdmb/showthread.php?t=54869&highlight=shotguns+space) should help too. Similar question - Shotguns in Space and whether they would work. My first ever post that one. Old skool! ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [September 3, 2004, 1:59pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/27 "2004-09-03T13:59:15Z")
> [@SPOOFE](#): > > [Here’s a gun](http://www.stormingmedia.us/23/2308/A230891.html) that’ll do the job… So an enterprising astronaut with an ack ack gun could sit on the moon’s surface, and write his name in flames across the skies of earth. Ordinary lead bullets would likely vaporize on the way down, but a high melting metal like osmium should make it to the surface. ---
**Author:** ![Dancer\_Flight](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dancer_flight/32/7601_2.png) [@Dancer\_Flight](https://boards.straightdope.com/u/Dancer_Flight)\ **Post date:** [September 3, 2004, 2:22pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/28 "2004-09-03T14:22:10Z")
Earth-moon distance: ~385000 km Velocity of Projectile: 3 km/s Simplifying assumptions: Neglect the velocity loss due to climbing out of the gravity well and the attraction acceleration from the Earth; Also assuming the astronaut knows the correct location to fire at in order to intercept the earth. 385000 km x 1h x 1 d = 4.5 days. 3 km/s 3600 s 24 h It looks like the gunner could go take a long nap and get some coffee before the show 😃 -DF ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [September 3, 2004, 2:34pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/29 "2004-09-03T14:34:54Z")
So, your science teacher shows only minimal understanding of nature, and less understanding of inquiry science, and your English teacher is apparently unable to impart the basics of spelling… > [@](#): > > I was in school today and we were talking about how their is little gravity on the moon (This use requires “there,” not “their”) My recommendation: READ Try this forum on a regular basis. Use the internet to discover good questions - and answers. Try books - they’re not out of date yet. (notice that spelling, by the way) As Wilson Mizner wrote, “I respect faith, but doubt will get you an education.” And Mark Twain said, “I never let schooling interfere with my education.” Attend to these wise men. ---
**Author:** ![The\_Flying\_Dutchman](https://avatars.discourse-cdn.com/v4/letter/t/9fc348/32.png) [@The\_Flying\_Dutchman](https://boards.straightdope.com/u/The_Flying_Dutchman)\ **Post date:** [September 3, 2004, 2:48pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/30 "2004-09-03T14:48:28Z")
For those who are adept at it and inclined to do so, what is the muzzle velocity required for a 6 foot man to shoot himself with a rifle having 10 foot barrel on an airless moon? ---
**Author:** ![aegypt](https://avatars.discourse-cdn.com/v4/letter/a/76d3ee/32.png) [@aegypt](https://boards.straightdope.com/u/aegypt)\ **Post date:** [September 3, 2004, 3:03pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/31 "2004-09-03T15:03:26Z")
> [@CC](#): > > My recommendation: READ Sheesh, don’t be so hard on the guy. We all make mistakes. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [September 3, 2004, 3:09pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/32 "2004-09-03T15:09:13Z")
> [@aegypt](#): > > Sheesh, don’t be so hard on the guy. We all make mistakes. No kidding. Joss Whedon screwed this one up in _Firefly_–the gun guy said his assault rifle couldn’t fire in a vaccuum. Matchlocks, however, are right out. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [September 3, 2004, 3:15pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/33 "2004-09-03T15:15:43Z")
> [@Squink](#): > > Ordinary lead bullets would likely vaporize on the way down, but a high melting metal like osmium should make it to the surface. Osmium (T[sub]m[/sub]= 3000[sup]o[/sup]C, T[sub]b[/sub]= 5500[sup]o[/sup]C, [symbol]r[/symbol] = 22.4 gcm[sup]-2[/sup]) would be better than lead (T[sub]m[/sub]= 325[sup]o[/sup]C, T[sub]b[/sub]= 1740[sup]o[/sup]C, [symbol]r[/symbol] = 11.4 gcm[sup]-2[/sup]) at surviving entry into Earth’s atmosphere, but the gun couldn’t get it to anywhere near escape velocity because of its density. (Assuming the bullets were similar in size.) Try Molybdenum (T[sub]m[/sub]= 2610[sup]o[/sup]C, T[sub]b[/sub]= 5560[sup]o[/sup]C, [symbol]r[/symbol] = 10.2 gcm[sup]-2[/sup]) ---
**Author:** ![flamingbananas](https://avatars.discourse-cdn.com/v4/letter/f/f4b2a3/32.png) [@flamingbananas](https://boards.straightdope.com/u/flamingbananas)\ **Post date:** [September 3, 2004, 4:17pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/34 "2004-09-03T16:17:09Z")
> [@CC](#): > > So, your science teacher shows only minimal understanding of nature, and less understanding of inquiry science, and your English teacher is apparently unable to impart the basics of spelling… > (This use requires “there,” not “their”) > > My recommendation: READ > > Try this forum on a regular basis. > Use the internet to discover good questions - and answers. > Try books - they’re not out of date yet. (notice that spelling, by the way) > > As Wilson Mizner wrote, “I respect faith, but doubt will get you an education.” > And Mark Twain said, “I never let schooling interfere with my education.” > > Attend to these wise men. I do read. It was one mistake. I can spell fine. I do read this fourm on a regular basis. This was a question, I put it in the correct fourm, these people are giving answers. Chill out. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [September 3, 2004, 4:41pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/35 "2004-09-03T16:41:16Z")
> [@grienspace](#): > > For those who are adept at it and inclined to do so, what is the muzzle velocity required for a 6 foot man to shoot himself with a rifle having 10 foot barrel on an airless moon? Is he unladen? An African man or a European man? Are there coconuts involved. I know this is a trick question is to figure out the orbital velocity for 6’ altitude but you’ll need to frame the question tighter as the man could simply fire straight up and let the bullet fall on his head. Muzzle velocity would not matter and in fact the bullet would impact with a tiny amount more velocity than when it left the muzzle as it will fall an additional four feet from it’s starting point. ---
**Author:** ![InvidiousCourgette](https://avatars.discourse-cdn.com/v4/letter/i/e47c2d/32.png) [@InvidiousCourgette](https://boards.straightdope.com/u/InvidiousCourgette)\ **Post date:** [September 3, 2004, 4:43pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/36 "2004-09-03T16:43:41Z")
> [@grienspace](#): > > For those who are adept at it and inclined to do so, what is the muzzle velocity required for a 6 foot man to shoot himself with a rifle having 10 foot barrel on an airless moon? The two equations you want are: 1. Force of gravity attracting the bullet to the moon = G.m1.m2/r^2 2. Centripetal force required to keep bullet in a constant orbit = m2.v^2/r Solving gives: v = (G.m1/r)^0.5 Where v is the required muzzle velocity, G is the gravitational constant, m1 is the mass of the moon and r is the radius of the moon. m1 = 7.35e22 kg G = 6.67e-11 Nm^2/kg^2 r = 1.738e6 m Hence the required muzzle velocity for a gunman to shoot himself in the back on the moon is 1.679 km/s The bullet will hit the gunman 6.5 seconds after he pulls the trigger, should he be sufficiently accurate with his shot. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [September 3, 2004, 4:44pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/37 "2004-09-03T16:44:25Z")
Don’t let them bust your chops **flamingbananas**. Well make grammar and spelling mistakes when our fingers outpace our brains. I thought your question was a good one as the answer is not obvious if you don’t know certain details about guns and ammunition. ---
**Author:** ![Cerowyn](https://avatars.discourse-cdn.com/v4/letter/c/82dd89/32.png) [@Cerowyn](https://boards.straightdope.com/u/Cerowyn)\ **Post date:** [September 3, 2004, 4:49pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/38 "2004-09-03T16:49:41Z")
> [@RickJay](#): > > The Earth is in fact the densest of all planets and moons. It is the densest large object in the solar system except the Sun itself. [Hijack for cool fact]: The Earth is only denser than Mercury because of gravitational compression; if Mercury was Earth-sized, it would be more massive. One more reason that I’m fascinated by the [MESSENGER](http://www.nasa.gov/mission_pages/messenger/main/index.html) mission. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [September 3, 2004, 5:09pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/39 "2004-09-03T17:09:44Z")
> [@Padeye](#): > > Well make grammar and spelling mistakes when our fingers outpace our brains. Yes we does. 😉 Good question **FB**. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [September 3, 2004, 5:22pm UTC](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849/40 "2004-09-03T17:22:56Z")
> [@InvidiousCourgette](#): > > Hence the required muzzle velocity for a gunman to shoot himself in the back on the moon is 1.679 km/s > > The bullet will hit the gunman 6.5 seconds after he pulls the trigger, should he be sufficiently accurate with his shot. So the Moon is only about 10 km in circumference? Assuming your calculations of the speed are correct, it would take almost two hours for the bullet to come around. [Previous page](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849.md?page=1) [Next page](https://boards.straightdope.com/t/how-fast-does-a-bullet-travel-on-the-moon/262849.md?page=3)