Rockets

"Matthew F Funke" wrote in message
...

No disagreement here. I just wanted to avoid the notion that a
rocket needs to "push against" the ground, air, previously expelled
propellant, or any other thing that is sitting out the back end when the
rocket fires in order to work. (Rockets work better in vacuum than in
air, in fact.)


Right. I think ultimately we're in agreement here.


--
-- With Best Regards,
Matthew Funke )

Ian Woollard wrote:

Joann Evans wrote in message ...
Ian Woollard wrote:

Joann Evans wrote in message ...
rockets ... are the only way known in current physics to make
something move in a vacuum.

That's not actually true; electromagnetic tethers and solar sails also
work among several other options.

Okay, but Newton's Third Law is still involved, momentum is still
transferred.

Big deal, Newton's third law and momentum transfer happen when I play
basketball. That doesn't make me a rocket either.

Are you playing it in free fall? Throw that basketball, and see what
happens to you. Basketballs are acceptable reaction mass.

Rockets have one or more rocket engines. Neither an electromagnetic
tether nor a solar sail have rocket engines.

Repeating: okay.

I agree with that. Strictly speaking, this is not a rocket.

"Joann Evans" wrote:
And indeed, as an atmosphere *impedes* the exhaust gases, rockets
work *better* in vacuum, and are the only way known in current physics
to make something move in a vacuum.
[snip]

This depends much more on the definition of vacuum than on
anything else. If your definition is the ordinary definition
then this is not true, as solar sails, mag sails, and
electrodynamic tethers can change momentum in the "vacuum"
of space. If your definition is a gasless, "perfect vacuum",
then there are still solar sails and electrodynamic tethers.
Only when you consider absolute, perfect vacuums without
light, or any force gradients would your statement be true.

In article ,
John Schoenfeld wrote:
...
... ellastic. ...
...
... ellastic ...
...

I have often wondered why idiosyncratic misspelling
so often coincides with crackpotism. Anyone know?
(It is certainly a helpful shibboleth.)

"Bruce Janson" wrote in message
...
In article ,
John Schoenfeld wrote:
..
... ellastic. ...
..
... ellastic ...
..

I have often wondered why idiosyncratic misspelling
so often coincides with crackpotism. Anyone know?
(It is certainly a helpful shibboleth.)

Speaking for myself, the poor spelling and crackpotism
are both caused by a self inflicted education. I've been thinking
about suing myself for the defficiencies in learning.

John Hare

(Bruce Janson) writes:

In article ,
John Schoenfeld wrote:
..
... ellastic. ...
..
... ellastic ...
..

I have often wondered why idiosyncratic misspelling
so often coincides with crackpotism. Anyone know?
(It is certainly a helpful shibboleth.)

For one thing, crackpots typically are ill-educated to un-educated ---
which they often view as giving them an "advantage," since to their minds
it means they are not "hidebound" or "constrained" by "conventional thinking."

Regardless of their level of formal education, crackpots generally grossly
over-estimate their own mental competence, typically considering themselves
to be "brilliant" or even "geniuses," when in reality they are of sub-normal
intelligence, and are often incapable of forming even a coherent sentence,
let alone a coherent thought.

It is an interesting phenomenon that the incompetent generally
over-estimate their own abilities, while the highly skilled generally
under-estimate them. See "Unskilled and Unaware of It: How Difficulties
in Recognizing One's Own Incompetence Lead to Inflated Self-Assessments,"
http://www.apa.org/journals/psp/psp7761121.html.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

Joe Strout wrote:

[snip]

All that needs to be done is to make the upwards push a greater
impulse than the downwards push - the rocket would essential jerk its
way upwards - after all there is no "conservation of displacement"
with such an inertial system.

There is conservation of momentum, and you just proposed to violate it.
This is a stiction (static friction) drive, and works only when in
contact with some other body. The movement comes from the difference
between static and sliding friction. And, BTW, if you want a drive that
only works when in contact wiith a larger body, there are much better
ones (the wheel comes to mind).

Such a drive is utterly useless in space, however. Jerk your rocket
around all you want, it'll never make any net progress at all.

Cheers,
- Joe


One more reason for cheap access at least to LEO: Everyone who thinks
they've got a reactionless drive can take a prototype up there, put it
outside the ship, and then they can put up, or shut up.

(I know, there are cheaper ways of doing this [suspend it, and see if
you get a unidirectional deflection, instead of gyrating or oscillating
around the perpindicular], but my approach is instinctively unambiguous.
This, after all, is where the thing is supposed to work.)

It would be even more interesting, if the losers have to find their
own way back to the ground.....

John Schoenfeld wrote:

[snip]

Um, yes, it is.

No it is not. Imagine a stationary black-box floating in space. One
wall of the box is hard iron and the opposite side is ellastic. If a
ball is thrown from the middle at the hard iron wall there will be a
high-impulse transfer of momentum from the ball to the box. Relative
from the center of the box (which at this point is moving), the ball
now approaches the opposite ellastic wall in which it inevitably
collides with and transfers the same momentum but in the opposite
direction bringing the box to rest again. However, the elastic wall
collision was low-impulse and took longer for the momentum to be
conservered. Irrespective of momentum conservation, there is an
overall displacement.

At this point we have the box at rest yet it is displaced from its
original position, however in future time this same effect will occur
but in the opposite direction and thus the overal motion of this
contraption would be to OSCILLATE about the original position. So
technically speaking, its not inertial propulsion yet as the center of
mass is constant.

So the third and final requirement would to have a constant stream of
balls colliding just as the first one thus always staying one step
ahead of the "backwards oscillation phase".

I think some past claims of reactionless drives that allegedly
reduced their weight (though never to zero, it seems) on scales, had
more to do with a similar phenomenon in the springs of the scale, then
actually providing a net upward force. Time your oscillations right, and
you can fool the scale, but not Mother Nature....