SpudFiles

DYI wrote:

Can I ask one thing DYI? Since the airsoft bb went through aluminum, does that mean it could possibly go through kevlar? If you can, could you test that theory for me please? I just wanted to prove a point to a friend, that with the right amount of power that it is possible.

How much Kevlar?
I'll add to what Fnord said (which is quite accurate as far as I'm aware) that the low density of Kevlar works against it in this case - when the impact behaviour becomes essentially hydrodynamic in nature, the density of the target usually makes more of a difference than the mechanical properties. Also, Kevlar doesn't work too well even against low speed projectiles when it isn't properly supported - stretch it out across a frame, and nearly any respectable projectile will punch through. Pack it with fabric on top and underneath and sit it loosely on a soft target, and it does a great job.

How much? Just like a 5"x5" Square, it doesn't have to be an actual vest, I just would like to prove to my friends that it is possible. This is what one of my friends said, "Its physically impossible to put an airsoft bb through kevlar, the bb would shatter before the kevlar even got a dent in it. You probably won't even be able to make a gun that can put an airsoft bb through sheet metal."

warhead052 wrote:"Its physically impossible to put an airsoft bb through kevlar, the bb would shatter before the kevlar even got a dent in it. You probably won't even be able to make a gun that can put an airsoft bb through sheet metal."

That shows a fundamental lack of understanding of how kevlar vests work.

You can cut inches of steel with a jet of water if it's travelling fast enough.

[youtube][/youtube]

jackssmirkingrevenge wrote:You can cut inches of steel with a jet of water if it's travelling fast enough

Just takes 70k psi+, we have one at work but the abrasive kind, it only runs at 40k psi.

Warhead, it's never worth proving your friends wrong, costs you time, and loses friends. Anything going quick enough will go through almost anything to answer your question.

before the kevlar even got a dent in it

?

If Kevlar stayed rigid on impact it would not be so bullet resistant...

You probably won't even be able to make a gun that can put an airsoft bb through sheet metal

Makes sense...


It's as impossible as an invisible tank!

You need to link this topic to your friend...

Warhead, your friend has no idea how projectile protection based around Kevlar works, as mentioned by the above posters.

The airsoft round will shatter (ripped apart by tensile shockwaves generated at the target-projectile interface, which is at well over 10GPa in this case) on impact with anything relatively solid - 1/8" aluminum plate, for example. At speeds where the impact is essentially a hydrodynamic phenomenon, whether the projectile is in one solid piece or a cloud of dust doesn't make much difference - the sectional density is the same, and thus so is the momentum or energy per unit surface area. A drop of water the same volume at that speed will have very similar impact characteristics, of which the water jet cutter is a nice example.

If they did, they would be the laughing stock of the scientific community. You only get out the energy you put in. This is not going to be done on just the power grid of the US or any other nation, even when using the entire output of the grid. It's not near enough power.

In regards to the airsoft round passing through the earth.. If it tries to accellerate a core of the planet on the way through, it would take on that mass as it punches a hole, this would transfer energy and reduce the mass of the round as it slows while the mass of the core pushed aside would gain mass due to the acceleration. I expect the result would be a huge explosion from the release of energy. It would be much larger than the Siberia explosion from about a century ago where a much slower particle impacted the air. A smaller particle at much higher speed impacting the core would do this to the solid core what the larger one did to the air.

http://en.wikipedia.org/wiki/Tunguska_event

Firstly, I'd like to say that I got the speed wrong - it's MUCH closer to c than I stated before, only off by about 10^-28 m/s.
Now, to respond to Tech's statement about energy release:

(EDIT: although the following is "pretty", it's also wrong. As the edit in my earlier post states, the round will not experience gravitational collapse, and to treat this problem in a purely special-relativistic sense is fallacious. The airsoft round would be scattered on impact regardless of its velocity, releasing all its energy at the surface.)

If the round was still in the form of atomic (or electron-degenerate) matter, it would probably be scattered on impact and release essentially all its kinetic energy as high frequency EM radiation.

As we get to higher mass density though... We get into areas that nobody fully understands yet. If singularities are a physical reality (or at least the actual diameter is low enough to make the following roughly accurate), as opposed to simply a mathematical artifact, then the following would be the case:

The singularity (which masses 110 billion tonnes) has an "actual" diameter of 0, so it does not "collide" with any of the matter that it passes through. It has a Schwarzschild radius of 1.63 * 10^-13 m. It is moving relative to the matter it passes through at almost exactly lightspeed, so only the mass within that radius would be captured by it as it passed through. This gives a core with a cross sectional area of 4.25 * 10^-25 m² which would, using Earth's average density, have a mass of about 1.5 * 10^-10 grams.

Now, using momentum conservation, I get...
Well, I must admit that I was expecting a lower number. Not counting the effects of the mass being constantly added as the particle moves (i.e., modeling it as an inelastic collision, this is still accurate to at least within an order of magnitude), I get an energy loss of 10²⁴ J during the transit through the Earth. That's 238 MT/m of its path through the Earth (assuming it went right through the centre). So, while it wouldn't destroy the target, it would certainly make for quite an impressive show. Energy release equivalent to a 20km bolide at 10km/s. Most of that energy release wouldn't affect the Earth's surface, but you'd still be looking at an extinction level event (although certainly a recoverable one).

In conclusion, singularities are very inefficient projectiles, but the one in question here would still punch a transient hole a few hundred metres (possibly several kilometres) across right through the Earth (and the entrance and exit holes would be craters probably over ten kilometres across). So now we reach the old answer yet again, in a more thoughtful manner - accelerate something fast enough, and it will destroy any target. It just becomes a very inefficient process after the target can no longer scatter the projectile.


EDIT: if anyone feels like wasting an hour or so with an arbitrary-precision calculator to verify my results or improve anything, I've been using a Lorentz factor of exactly 556 * 10¹⁵, and a 0.2g airsoft round.

hi to everyone, this is my first post and really i have to congratulate DYI your perseverance in your work and your launcher are amazing really is something to admire. i never imagine was possible to build a hypervelocity launcher for the hobbist but you prove me wrong
sorry my english isnt to good

DYI, tech, Brian, and Zeus, I am going to link this to my friend, and wait for his reaction.

Brian, I proved my friend wrong today, I shot through my sheet aluminum shed, about 2mm thick with an valveless concept using an oring and 200 psi. My dad is kinda pissed about it, so no more launches like that for me until I can replace the aluminum....

warhead052 wrote:My dad is kinda pissed about it, so no more launches like that for me until I can replace the aluminum....

Are you surprised?

Not really. I knew he would be pissed, but I didn't think it would actually go through. Seeing as I was standing like 20 feet away.

Little late on my part, of course, but good execution again, DYI. Are we running out of propulsion methods yet?

Also,
<jack_black>Yeah! SPALL!</jack_black>

Nice job, decent efficiencies too. Where did you get your capacitors?
Your chamber support looks a bit excessive to me. Is this just for sealing?

mark.f wrote:<jack_black>Yeah! SPALL!</jack_black>

*arm falls off*