🚀 go-pugleaf

In article <1993Jan2.053258.5064@adobe.com>, pngai@adobe.com (Phil Ngai) writes:
> In article <30DEC199200153934@pierre.mit.edu> chuck@pierre.mit.edu (Chuck Parsons) writes:
> >  Second mechanical strength of materials is _not_ greater than the
> >strength of the chemical bonds forming the material. 
> 
> In a flywheel, there is a relationship between material strength and
> stored kinetic energy, but it is hardly 1 to 1. This would be almost

Correct - it is worse.  Check my post on direct comparison of energy stored
to bond strength in the material based on C-C bonds at graphite density.
Even if the flywheel could be spun to the limit of the theoretical material
strength, it could only store half the energy represented by the bond
strength before the atoms flew apart.  Comparing this energy density
to that of gasoline proved very unfavorable.  When a maximum material
strength of 1 Mpsi for carbon composite was used in the calculation, a
minimum rotor mass of 510 kg was obtained.

> like arguing that the kinetic energy of a bullet or meteor is limited
> to its material strength.

No.  All kinetic energy is not created equal.  Storing kinetic energy
in a flywheel necessarily stresses the material since it is under
continuous acceleration.  However, I can establish an inertial reference frame
on any bullet or meteor (in a vacuum) in which that object has zero kinetic
energy.  There are no forces acting on the object, so it is not under stress.
No inertial frame can be established on the rotor to change its stored
kinetic energy due to rotation - this energy is the same in all inertial
frames.

Therefore it is indeed true that energy storage in a flywheel is limited
by material strength.  But in a collision, a meteor or bullet is only
limited by relativity considerations in the energy it can contribute to
the collision.


--
Richard Stead
Center for Seismic Studies
Arlington, VA
stead@seismo.css.gov