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From: John De Armond
Subject: Re: Flywheel batteries - this is really disgusting
Message-ID: <>
Date: Sat, 19 Dec 92 21:18:15 GMT

stead@skadi.CSS.GOV (Richard Stead) writes:

>Look what up?  The melting temperatures for ceramics?  Lots of references,
>but you don't understand the physics here.  The particles have so much
>energy that they will melt any solid in existance.  This has more to
>do with the molecular behavior of the material - the impact velocity is
>so high that the atoms are forced well beyond any sound speeds.  They
>then form a shockwave, completely disordeing the material, leaving it
>in a fluid state and creating a great deal of heat.  Just check some
>sound velocities and compare that to the velocity of the particles from the
>rotor.  That starts to give you an idea of what kind of regime we're in.


Thanks for bringing some sanity to this disucssion.  Frankly, I've been
so sickened by the thorough ignorance of basic physics displayed in
this thread that I didn't jump in.  Your description of the knetics involved
is of course, right on the mark.

Here's another perspective.  Back in the early 70s when I was in school,
we were doing some research for NASA on micrometeor impact.  Our research
was conducted using a hydrogen gas gun we built to accelerate BB-sized
pellets of various materials to hypersonic speeds.  A BB shot from
this gun would penetrate 18" or so of steel and leave a melted hole
6" or so in diameter.  When it didn't penetrate, it spalled a parabolic
chunk out the other side so that a cross section of the target looked
like an hour glass.  More interesting, a pellet of plexiglass penetrated
almost as deep.  Demonstrates how much mass vs velocity (squared)
contributes to the energy.  All experiments were conducted in a high
vacuum chamber because air friction would heat any projectile to
incandescence practically by the time the projectile left the barrel.

We studied the impacts using photographs taken by a camera capable of
almost 20,000 frames per second and high speed air-arc lights.  The point
of impact was particularly interesting.  Practically upon the first
contact, the projectile was transformed to a glowing plasma flame.
This flame melts and shocks its way into the material.  When shooting
plexiglass targets, the shock wave could be seen forming in the
target even without polarizers or other image enhancements.

The velocities we achieved are in the same order of magnitude as the
peripheral velocity proposed for some of these flywheel batteries.
In my book, that makes the battery a bomb just waiting to detonate.


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