From: lwcamp@gmail.com   
      
   On Thursday, September 1, 2016 at 2:57:29 PM UTC-7, MrAnderson wrote:   
      
   > So for now, I give the projectile mass of 0.5 g, which at 200 km/s is   
   10000000 Joules if my calculations are ok, so it's around two kilograms of TNT   
   coming at your face.   
      
   That's about right.   
      
   If you keep the same dimensions for your bolt, this gives you a density of   
   0.05 g/cm^3.  Consequently, at Earth-standard atmospheric pressure and   
   temperature the bolt will travel a distance of about 3 meters before it is   
   ablated away by its high speed    
   passage through the air.   
      
   > I don't remember how to calculate all of the quantities with recoil, I don't   
   remember anything after my holidays, so could you help me with this?    
      
   Recoil momentum is equal to the projectile momentum   
   p = m v   
   where p is momentum, m is projectile mass, and v is projectile speed.    
      
   Recoil energy is the kinetic energy of the gun due to its momentum   
   E = p * p / (2 m)   
   where E is the gun's kinetic energy.   
      
   > I know the full idea of plasma weapons, non existent fields keeping them in   
   place is *dumb* in most places, but you know, they are just nice ;>    
      
   Note that if you just shoot out a tungsten slug (or any other solid   
   projectile) at 200 km/s, it will quickly become a plasma.  As it punches its   
   way through the air, the air at the shock wave at the front will be   
   compression heated to a brilliant plasma (   
   which in turn heats the front of the projectile and the material ablated off   
   the projectile to a plasma.  At these speeds, the shock in the projectile   
   itself might heat the projectile material to a plasma as well).  So this is   
   one way to get around that    
   pesky virial theorem - just use a solid material to get confinement and let it   
   form a plasma as it goes.   
      
   > Also, do you know about experiments with containing plasma in open air? The   
   first one I know about is the MARAUDER, US project for anti missile plasma   
   cannon, from whai know failure, and second is not so old, I recall watching a   
   video of 1 foot plasma    
   ring in free air, I don't know where did I see this, it was from 2010 at most.   
      
   Plasma in open air is stable because it is being compressed and contained by   
   the pressure of the surrounding atmosphere.  This limits your plasma to a   
   pressure of one atmosphere.  The energy contained in the plasma at equilibrium   
   is thus going to be    
   approximately 1.5 * P * V, where P is the plasma pressure and V is the plasma   
   volume.  The factor of 1.5 might change by a small amount if you are in a   
   regime where the plasma atoms are readily gaining or losing electrons as it is   
   further heated or    
   compressed but that can be neglected for these back of the envelope   
   calculations.   
      
   So for a 0.5 cm diameter by 50 cm long plasma bolt, you would have about 8   
   joules of energy as thermal energy of the plasma.  This is less than a   
   firecracker.   
      
   Luke   
      
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