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# Physics/How many G's can a tungsten projectile endure?

Question
QUESTION: Hi! I was wondering how many G's can a railgun launched tungsten projectile take without breaking apart because I'm starting to write a scifi story and don't want to make spaceship weapons exceeding what real physics allow them to do. So assuming a railgun length is 9 meters and let's consider the acceleration linear. How many g's can a railgun projectile take and what velocity does it correlate to? And the projectile weights are 9 kilograms and 18 kilograms. Is a velocity around 6 kilometers/second close to maximum or what velocity is maximum before the projectile/railgun breaks apart?

ANSWER: Only 9 meters?  Wow, that is reeeeally short for a rail gun.  There are really not many physical limits.  You're also talking about reeeeally small projectiles.  With such small masses, in theory there's nothing keeping you from achieving the 200,000 g's necessary to get solid tungsten up to such a low rail gun velocity.  I mean, bullets fire from pistols at something like 4000 g's and are only made of lead...but you have to at least be able to say that the sudden pulse of electrical current was designed to keep the projectile from slagging itself.  If I were you and this were some kind of a spaceship, I'd definitely allow for a longer barrel by maybe a factor of 10 (a barrel can stick out from a ship) and worry more about accounting for the change in velocity of the ship upon firing.

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QUESTION: What velocity could a 90 meter railgun have with let's say 35 kilogram projectile and if that is too small let's make it 350 kilogram projectile?
Could a 90 meter long railgun on a space ship accelerate a 350kg projectile to six kilometers per second velocity and how much would recoil be a problem for this ship that has mass of 200000 metric tons? Would recoil change the velocity of the ship by a great deal or would the ship be fine with this recoil? And could I get the simplest form of mathematical/physics formula explained in determining the recoil and the g forces it would bring cause to the ship?

It probably could, that's somewhat realistic for a pure tungsten shell.  You can multiply mass*velocity and tell me the change in velocity of the ship...it's equal to the mass*velocity change of the shell (conservation of momentum).  That's how you determine the recoil.  Set final energy equal to force*distance on the shell (F*dist = mass*accel*dist = (1/2)*mass*velocity^2)  Mass will cancel out if you just use the last two terms and you'll end up with the acceleration of the shell.  The acceleration of the shell will be "a."  "a"*(mass of shell/mass of ship)= acceleration of ship.  Divide by about 10 (9.8, precisely, but about ten for literary work) to get it in g's.  200,000 metric tons is 200,000,000 kg, so I figure it'll be detectable but small.

Physics

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#### Dr. Stephen O. Nelson

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I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

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I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.