A question of credibility

[unknown]

sts60 wrote:
"1. "Bending moment" isn't what you're thinking about. Try Googling up another random term and see if we're any more impressed next time".

In the space moments of the forces (o.k.?) are infinite and an object hanging on the bottom will roll down in any directions.

I want to make an example for children:
if you, dear little child, put your forefinger under a can of coke you'll see that it will fall down in any directions and you will not able to keep it "in hovering".
If your forefinger was a magnet and the can was made by iron, you easily could lift the can sustaining it from the top. ;D ;D ;D

[DaveC]

Isn't it time to just ignore any further drivel from unknown? Isn't that the best way to deal with a troll?

[Bob B.]

davec said:

Isn't it time to just ignore any further drivel from unknown? Isn't that the best way to deal with a troll?

Agreed.

[martin]

bob said:

davec said:

Isn't it time to just ignore any further drivel from unknown? Isn't that the best way to deal with a troll?

Agreed.

He can not read what we are writing any way, since we are too far to be seen

Martin

[sts60]

In the space moments of the forces (o.k.?) are infinite and an object hanging on the bottom will roll down in any directions.
No. Being in space has nothing to do with it, and neither the forces nor the moments involved are infinite. That's either two more errors, or three, depending on how you count it.

Furthermore, while any thrust not aligned with the center of mass will induce an overall torque on the vehicle, that does not mean a vehicle is inherently unstable, as you seem to think. Another error.

Finally, bottles poised on fingers don't have guidance systems, nor two independent types of reaction mechanisms to counteract unwanted R/P/Y rates. A real whopper of an error. Anyone who took about 100 seconds to Google "lunar module" and look at a page or two would figure this one out.

[JayUtah]

I suggest you to begin with bending moment.

LOL! Bending moment has absolutely nothing to do with flight dynamics. You're simply Googling around for random concepts you think can apply to your argument. I'm an engineer; I can write at least a thousand words off the top of my head on the subject of bending moment. You were obviously just introduced to the concept

Bending moment describes the force applied to a cantilevered member such as to induce bending (transverse load) or buckling (axial load) strain. The precise geometry of the cross section in combination with Young's modulus govern how much bending moment is required to bring about deformation.

You want simple moment, which is merely any rotational force. Yes, that is an important concept in flight dynamics, but it is quantitatively discussed -- not merely the handwaving you have demonstrated. It must also be discussed in connection with moment of inertia, on which topic you have expressed uncommon ignorance.

Moment is defined as a force acting a certain distance from a body's center of gravity, in a direction perpendicular to that dimension. The resulting angular acceleration depends on the body's moment of inertia and the magnitude/distance of the moment.

Normally a rocket motor's thrust vector points along a line connecting the center of thrust (the rocket's throat) with the center of mass. It can point in either direction. Off-axis thrust results when that vector is not parallel to the connecting line -- the thrust basis. The distance from the throat to the center of mass is the moment arm length. Decomposing the off-axis thrust vector along that dimension produces the moment magnitude. The rotation rate is this moment divided by the vehicle's moment of inertia.

If you take the time to do the vector mathematics, you discover that this is the case regardless of the orientation of the relationship between engine and center of mass. That is, the decomposition produces an identical moment regardless of whether the center of mass is ahead of or behind the center of thrust. The resulting vectors, reckoned in the thrust basis, are identical.

That is the formal proof of the theorem.

You argue that gravity, in the "pendulum" model, should return the vehicle to equilibrium. But gravity, by definition, operates at the center of gravity -- and only there. It cannot, by definition, create a correcting moment because the length of any moment arm relating to gravity is, again by definition, zero.

So how does a pendulum work?

It works because the clock and pendulum have two different bases. ("Basis" is the linear algebraist's term for what dynamicists refer to as a "reference frame". In either case it is a coordinate system that defines a vector space in which force computations can be consistently performed.)

The clock frame, including the pivot, is fixed in the basis of the room. The pendulum is a separate body having its own center of gravity and thus its own basis. The forces applied by gravity, and by the pivot, in the pendulum's basis oscillate. The force applied by the pivot to the pendulum, in the pivot's basis, is constant.

I have now given you the formal vector underpinnings for your claims regarding flight dynamics. You claim I am uneducated and inexperienced in the nature of the applications of force in dynamics. You're still fumbling around trying to find the right terminology.

Refute this with mathematical rigor, if you can.

[JayUtah]

In the space moments of the forces (o.k.?)...

No, not okay. "Moment" and "bending moment" are two completely unrelated concepts. One discusses dynamics. The other discusses the mechanics of materials. "Moment of force" is meaningless.

...are infinite and an object hanging on the bottom will roll down in any directions.

No.

if you, dear little child, put your forefinger under a can of coke...

Irrelevant as there are two frames of reference in your example -- one for your finger and another for the can. I have proved my point mathematically. You have not. You keep returning to this example even after it has been rigorously shown not to apply to rocketry.

You clearly have no experience in dynamics, as evidenced by your fumbling misuse of terms and concepts. And your condescension offered up from the position of extreme ignorance is now simply annoying.

You are a petulant child, and I will not suffer it.

[sts60]

Ouch. I believe this is what's called a "woodshed" moment. As in, "Pa done took him out behind the woodshed."

[unknown]

JayUtah wrote:
"Refute this with mathematical rigor, if you can".

Hey, JayUtah
Mathematics is a rigorous discipline if you do operations using its relationships in its ambit.
When you apply mathematics to physics you can't consider all the various angles (because you don't know which they are) and you simplify the big complexity of problems and think vangloriously to have understood the enormous complexity of the universe.
Be quiet, little man, you know almost nothing about forces that reign in the universe.
In fact you are so small that you don't understand what even a child can realize.
Nobody in 1969 (and perhaps even today) could pilot that nice old crock (Lunar Module) thrusted from the bottom driving it being seated inside.
If you don't understand this simple thing, you are a big idiot and your mathematics has distroyed your little brain. ;D ;D ;D

[RAF]

unknown said:

Hey, JayUtah...snip...Nobody in 1969 (and perhaps even today) could pilot that nice old crock (Lunar Module) thrusted from the bottom driving it being seated inside. If you don't understand this simple thing, you are a big idiot and your mathematics has distroyed your little brain.

Well, that was an intelligent response...

I have no tolerance for "name callers", unknown. If you can't carry on a rational discussion, then just GO AWAY.

Then again...keep it up, and you could have the "honor" of being the first person banned on this "new" board.

[LunarOrbit]

unknown

Be polite or I will ban you.

Jay has brought up a lot of valid points that you have not refuted. It is clear to everyone except you that Jay knows what he is talking about, and you do not. Insulting him will not help you prove your case.

[Bob B.]

admin said:

unknown

Be polite or I will ban you.

One more post like the one above and I'll support this course of action.

[martin]

bob said:

admin said:

unknown

Be polite or I will ban you.

One more post like the one above and I'll support this course of action.

I support it now.

I think too many times, trolls are finding what they are wanting when they come here...

Martin

[Bob B.]

Unknown has been warned multiple times already and I don't expect any change in behavior. It seems obvious his/her goal is to do nothing but provoke and insult us. I think LunarOrbit's post should be considered a final warning with zero tolerance.

[LunarOrbit]

There will be no more warnings.