[TML] [OT] One for Gun Safty

[shadow at shadowgard.com]

On 14 Oct 2007 at 16:07, Jerry W Barrington wrote:

> On 10/12/07 11:34 AM, Kirk Bailey wrote:
> 
> > A recent arrival is the TL15 BB gun, which  tosses a tiny bit of metal
> > downrange at relativistic velocities.
> 
> Relativistic velocities in a man portable weapon?  How long is the barrel?

Given that it takes around 1000 km to accelerate a projectile to a 
few percent of c at 1 million gees, I don't see how the projectile 
can hold together.

Let's assume a 1 meter barrel.

d = .5 * a * t^2
v = a * t

rearrange the second equation
v/a = t

substitute into the first equation.

d = .5 * a * (v/a)^2
d = .5 * a * v^2 / a^2
d = .5 * v^2 / a

ok, substituing 1 meter barrel and 1% of c as the velocity.

1 = .5 * (3e7)^2 /a
a = .5 * 9e14
a = 4.5e14

That's 450 *trillion* gees!

No way in hell that's going to work. That level of acceleration, even 
if applied gravitically will rip the projectile (or the weapon) 
apart.

Also consider the energy inputs required. 

For a 1 gram projectile (0.001 kg) that's

E = .5 * m * v^2
e = .5 * 0.001 * 9e14
e = 4.5e11 

That's roughly one tenth of a *megaton*. And what are you going to 
make a 1 gram projectile out of so it won't vaporize on impact with 
the air. 






--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com