If the event you're trying to detect is the end of major acceleration,
of course, mechanical rebound or residual atmospheric friction could
actually work in your favor. The trick is to understand the forces
involved well enough that the mechanism works robustly and reliably.
On 12/1/2015 9:44 AM, Robert Steinke wrote:
And remember there exist no perfect vacuums any more than there are
perfectly inelastic ball bearings.
On Tue, Dec 1, 2015 at 9:07 AM, Henry Vanderbilt
<hvanderbilt@xxxxxxxxxxxxxx <mailto:hvanderbilt@xxxxxxxxxxxxxx>> wrote:
In an ideal perfectly rigid rocket or cannon projectile structure in
vacuum, that should be so. In the real world where the structures
will be to some degree elastic, removal of the accelerating force
will cause the structure to revert to its unstressed shape, which,
depending on design details, could then impart a force to your
ball-bearing or mercury droplet.
There's also the elasticity of the ball-bearing (or even, given
surface-tension, of the mercury droplet) which could also cause a
rebound once the overall acceleration ends.
As for the specific case of a projectile within a cannon barrel,
that depends on whether it is being accelerated for its entire time
within the barrel. This depends on the quantity and burn-rate of
the propellant charge. Typically the answer is yes, accelerated the
whole time, because calculating the propellant charge to still be
producing considerable positive pressure on the base of the
projectile as it reaches the muzzle tends to make best use of a
given length of barrel. It is however possible to use a small
fast-burning charge such that pressure has dropped off enough that
the projectile is decelerating by the time it reaches the muzzle.
On 12/1/2015 8:35 AM, John Dom wrote:
Just checking assumptions, please advise.
Am I right assuming a mercury droplet or loose ball-bearing will not
move forward inside a rocket in vacuum the instant the motor
stops? It
then only might start floating.
Nor will such droplet move forward inside a cannon projectile
after it
leaves the muzzle since on that instant push force has stopped.
As to
during the short residence time inside barrel, it might fly
forward I
reckon.
jd