# thrust does not work in space

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#### PmbPhy

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##### Re: thrust does not work in space
« Reply #100 on: 25/06/2014 10:12:54 »
Quote from: CitronBleu
To what empirical fact are you referring ?
Exactly what I was referring to, i.e. time and space have no affect on the pressure produced against the wall opposite the missing wall by the explosion. is an emperical fact. This doesn't happen.

Quote from: CitronBleu
To what laws of physics does this fact conform ?
All of them. Especially Newton's laws of physics.

Quote from: CitronBleu
My assumption, shared by others, is that man has never achieved flight beyond a hypothetical 80-120 Km altitude.
I see now. You're a conspiracy theorist who thinks that spaceflight to places outside that distance has never occured and that NASA and all the other space agencies on earth have lied to everyone on earth and everyon on earth bought it. Which means that hundreds of thousands of people in the world who work on it also lie and got away with it. And you're ignoring the fact that there are satelites in geosynchronous orbit around the planet which means that have to be at an altitude of 42,164 km.
http://en.wikipedia.org/wiki/Geosynchronous_orbit

Sorry but I won't talk to such people because I won't feed that kind of delusion past one post.

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Three hundred years ? That is it ?
No. You need to read more closely to what people write. I said well over 300 years. I know it was fact of Newton's thinking and those that came before him. I'm not that much of a history buff so I don't know how far back it does.

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You are right, humanity has never been known to be wrong for 300 years.
That's quite wrong. Newton's laws were found to be imprecise at atomic distances, at speeds close to the speed of light and in strong gravitational fields.

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Has sir Isaac Newton visited outer space perhaps to test the validity of his theories on classical mechanics ?
One doesn't need to be outer space to know that it's true. In anycase Newton used data provided by Kepler about the orbits of the planets who determined the orbits from the observational data that Tycho Brahe collected. In any case all one has to do is get a rocket engine and place it in a vacuum to establish that it works. And we know that it works because for salelites to be in geosynchronous orbit they have to be at an altitude of 42,164 km. And we know there there because that's how satelite TV works. The dish must point in exactly the same direction all the time which proves the satelites are that high.
The SCN presents all the major components of what can be defined as religion. Man lives among the gods (Jupiter, Pluto, etc.), human colonization of other planets will guide mankind to salvation, satellites will save us, etc.

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Then we were insulted for our efforts with the claim that all cranks use, i.e. that we're all brain washed and can't think for ourselves, which is utter nonsense.

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I thoroughly agree with your statement. You are among some of the brightest and most stimulating human beings on the planet, and true heirs to Thales of Militus.
Thank you. That is very kind of you to say.

Let me explain what's wrong with your beliefs. They can't be applied to anything because if they are they fall apart. For example; if Newton's third law holds then its wrong to believe it only holds in an atmosphere. And if it didn't work in a vacuum then some smart experimentalist would have figured it out years ago, long before we put many in space. You can't think that NASA is that stupid, do you? If Newton's third law didn't work then we'd be unable to walk or drive a car because the facts that it refers to are in operation when you're walking or driving a car. You're beliefs focus on a very small set of facts and ignores countless millions of experiments done in laboratories all over the world where these things have been tested in every concievable way, including in vacuum.

What I'll never understand about people like yourself is why you think that so many hundreds of thousands of use physicists are so morally bankrupt and so corrupted to lie as much as you think they are. I've never met a scientist that evil. You certainly haven't done anything to justify your claim that no spacecraft has ever been higher than you claim, that's for sure. In fact you didn't provide any reason why so many people would all agree to tell the same batch of lies.

So that's all for me. I don't talk to conspiracy theorists, even if they try to provoke me by challanges or name calling. Sorry.
« Last Edit: 25/06/2014 12:02:32 by PmbPhy »

#### jccc

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##### Re: thrust does not work in space
« Reply #101 on: 28/06/2014 02:32:54 »
If he had the chance to fart in space, he'll believe us.

#### dlorde

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##### Re: thrust does not work in space
« Reply #102 on: 29/06/2014 14:35:34 »
If he had the chance to fart in space, he'll believe us.
Not in a spacesuit, he wouldn't.

In space no one can hear you fart - but sooner or later they'll know...

#### jccc

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##### Re: thrust does not work in space
« Reply #103 on: 29/06/2014 18:35:20 »
If he had the chance to fart in space, he'll believe us.
Not in a spacesuit, he wouldn't.

In space no one can hear you fart - but sooner or later they'll know...

You are not helping him.

#### percepts

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##### Re: thrust does not work in space
« Reply #104 on: 01/07/2014 20:02:52 »

Isn't the point that the high energy material whether it be gas, water or something else is pushing against the space craft as well as anything else it comes into contact with and in all directions. The thruster nozzle pointing in one direction causes the push in the other direction to be directly opposite to the nozzle direction. The motion is caused NOT by the high energy material pushing against what is outside the spacecraft but by it pushing against the spacecraft itself.

i.e. completely flawed assumption in postulation that thrust motion is caused by pushing against what is external to rocket engine.

#### Reality207

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##### Re: thrust does not work in space
« Reply #105 on: 20/08/2014 03:46:01 »
I have read the objections to this statement and the arguments/logic behind it.
This subject has tormented me since childhood, as it does seem illogical that a rocket can work without resistance to push against.

Take the motorboat out of water and there is no resistance for it to push against.
Take the rocket out of atmosphere and there is no resistance for it to push against.

Ya sure Newton’s law “what you push against pushes back”, well if as in space there is nothing to push against or to push back, how can it be!!

I cannot explain why so many good scientists accept NASA's stories with such faith, but this is not a Conspiracy theory, it is logic.  You must reach and live with your own conclusions.  All I ask is that you don’t blindly accept what you were forced to learn and accept and that you apply logic for yourself.

Further, I ask, as flight controls also require atmosphere to react against and there is no atmosphere in space, logic would also demand that flaps, ailerons, spoilers and elevators would not affect the flight path of a space ship in space as they all require atmosphere passing by them to function.   Flight control - 101.

Now, realistically if we are to attain propulsion in outer space, logic demands it will have to be done by acting or reacting against something that exists in space.  If we are to attain flight control in space it will also have to be done by acting or reacting to something that exist in space.
I'm sorry but again we don't have that at this time, and no explanation of how thrust works without atmospheric resistance is known or offered.

Sorry Please don't hate me for these thoughts, I share with all due respect.
Offer me a logical explanation of how thrust works without atmosphere to push against.  Tell me how thrust can act or react without resistance.
Please don’t sight the example of throwing a ball standing on a skateboard or while sitting in a chair on wheels, as both of these experiments are conducted in atmosphere.

#### alancalverd

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##### Re: thrust does not work in space
« Reply #106 on: 20/08/2014 08:03:05 »
Have you ever fired a rifle? The recoil force is exactly the same whether you fire it under water or in air. Recoil force is independent of the surrounding medium.

Conservation of momentum is demonstrated in many ways: billiard balls, "Newton's Cradle", spinning tops and skaters.... and in no case is there any requirement of "something to push against".

Rockets work by conservation of momentum, nothing else. You chuck stuff out of the back and the rocket moves forward so that the net change in momentum is zero.

Interestingly, motor boats and aeroplanes work on exactly the same principle, except that the "stuff they chuck out at the back" happens to be the same ambient water or air that they are floating in, accelerated by the propellor. The difference with a rocket is that you carry the stuff with you as there isn't any ambient stuff to use.

You may have noticed that true space rockets http://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=xpmJJ5zcgCRSRM&tbnid=qpYSfLkBXvNeGM:&ved=0CAUQjRw&url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FAriane_(rocket_family)&ei=hkn0U_mDM4TK0QWE7oC4Dg&bvm=bv.73231344,d.d2k&psig=AFQjCNHgZpahKRn9bUN56MEe01OpAWmX0A&ust=1408604919233069 don't have flaps, ailerons or even wings. Have you asked why not? Directional control in space is done by pointing the rocket motor the way you want to go. The fins on the archetypal V2, and on air-to-air missiles, are for directional control whilst the machine is flying in air, which it does for most of the time.

Ultimately you are going to have to convince yourself. Not difficult. You can buy a model rocket motor, attach it to a spring balance, and fire it in a vacuum jar. Or just watch what happens if you energise an electric bell or a newton's cradle inside a vacuum jar. The absence of air makes no difference to the conservation of momentum.

The problem you will have is accepting that the laws of physics apply equally everywhere. Fortunately for the rest of the universe in general, and pilots and engineers in particular, that seems to be true.
helping to stem the tide of ignorance

#### aasimz

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##### Re: thrust does not work in space
« Reply #107 on: 20/08/2014 18:56:46 »
If you will allow me I believe I have the perfect explanation for that, I think any layman should grasp.

Because a one can argue with the cubes and spring example saying that the surrounding atmosphere has to be considered as one of the cubes, and the spring being the force of the expanding gas.

Thrust in space actually depends on the fact that there is nothing to push against in space. How?
Well it's very simple, imagine a box in space with 5 sides, one at the top and 4 on the sides and the bottom is open, if we triggered fuel reaction inside at the center of the box the (360 degrees) pushing force of the expanding gas will push against the 4 sides equally so the box will not move sideways, and will push against the up side and move it upward, but there is zero push toward the bottom because there is nothing to push against there.

We have to bear in mind that the rocket in space will have zero gravitational mass meaning much less force can make a big effect, so if you have something to push against, there will be gravitational mass which will lead to consume a lot more fuel.

I can safely say you can use your deodorant to spin in space, because the gas release will make it push against your arm that is limiting it is expanding speed, it is the gas trying to spread equally in all directions.

Out of this, I believe space is definitely not empty, actually it is absolutely full, there is no single Planck scale space that is empty in the whole universe, it's not only me, but more than 50 research groups of physicists around the globe and more are working on the Loop quantum gravity (LQG), where the theory predicts that not just matter, but also space itself has an atomic structure.
« Last Edit: 23/08/2014 14:50:44 by aasimz »

#### Reality207

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##### Re: thrust does not work in space
« Reply #108 on: 21/08/2014 02:13:51 »
First let me thank you for the gentlemanly reply, and the stimulating thoughts you provoked, in the words of my generation “groovy man”.
Rifle, I see it differently, for the sake of discussion, lets use a custom built device that will fire under water, in space and in the atmosphere.

First lets fire it in the atmosphere, as the gasses expands the projectile will push and compress the air in front of it as it leaves the barrel.  The gasses behind it will press against all side evenly, so the closed end, the barrel and the projectile will all see the same pressure.  The projectile will see resistance from its contact with the inside of the barrel as well as the displacement and compression of the air in front of it until it leaves the barrel.  As air compresses very easily the projectile will have no trouble exiting the barrel and will travel at a great speed until air resistance and gravity bring it to a stop.  I’m sure we pretty much all agree on that.

Second we fire the same projectile under water, the barrel will be full of water that must be displace, as water cannot be compressed, it will be difficult for the projectile to leave the barrel.  The projectile’s velocity will be decreased almost exponentially.  The projectile must displace the water in front of it that must displace the water in front if it and so on until the reaction reaches the end of the barrel.  At this point the displaced water will displace the water above the end of the barrel toward surface (assuming you fired the device horizontally) that will displace the water above it and so on until the reaction reaches the surface where that water will disburse.
As we take the device deeper and deeper into the water a fire it again the displacement becomes greater as more water must be displaced upwardly and projectile velocity decreases prospectively. Eventually we will get deep enough that the resistance will becomes so great that the pressure of the expanding gasses will exceed the displacement rate and the barrel will explode.
The projectile will not travel very far in water, as the resistance from water that must be displaced all the way to surface is extremely high.  Kick back will be greater as the pressure against the projectile is greater and velocity will decrease.  The kick back will also last longer, push harder and further, as the projectile will take longer to exit the barrel.

Lastly lets fire the device in space, as there is no resistance to the projectile exiting the barrel, the only resistance it will see is the friction between the projectile itself and the barrel.  The projectile velocity will be the greatest as the exit resistance is least.  The only kick back force that will result will be from the friction of the projectile against the inside of the barrel which will be minimal and the resulting kick back will be almost non-existent.  However the projectile will travel indefinitely, at the same velocity until it meets an object or other matter to influence its movement.
It’s all very simple, and I am not a layman, but a student of all sciences and an independent logical thinker, I think.lol

I have to say that I must rethink my statement that, “the only way space travel will be accomplished is to act or react on something that exist in space.”  I do believe that the kick back in space with the rifle though extremely small and short lived could produce a miniscule amount of propulsion in space.  If that kick back did occur in space it would do so without acting upon something that exists in space.

As the gun barrel has little to nothing in common with the rocket engine, which is to say that the rocket has no projectile to produce backpressure and thus propulsion, I have to maintain that I am not convinced sorry. No disrespect intended and I am very willing to listen.

The greatest number times zero is zero, the greatest thrusters against nothing (like in space) would seem to be zero and There is nothing to push against there how can there be a reaction?

Robert

#### Reality207

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##### Re: thrust does not work in space
« Reply #109 on: 21/08/2014 03:47:18 »
aasimz, Hi and thank you for your interesting response.

Someone a couple pages back added a diagram of two boxes and a spring in the middle between them both.  I would like to use that; one box represents the space ship, the spring represents the propulsion and the other box represents the atmosphere.  If we compress the spring and release it, both boxes will be accelerated equally provided both have the same mass and resistance....  but if we load the spring with only one box and release it, the box will not move, in atmosphere, in water or in space.  This is how I see the rocket in space, it is as a single box and spring with no resistance to move it and no movement.

Or to use your example if you place two five sided boxes with the open ends toward each other and explode something inside them they will then both be accelerated in opposite directions by pushing against each other.  This will prove true in atmosphere, water and space.  In space they will each continue all the way to the moon or the Milky Way or what ever they may strike along the way and at the same speed they started at.
But as I see it and this is only my logic, with one 5 sided box and one explosion: in water or atmosphere there is resistance and resulting propulsion, but in space I don't see it, no resistance, no propulsion.

Clearly I would not have graduated your college programs, they would have hated me and found a reason to expel me.

By the way, clearly propulsion is space is possible without acting or reaction against something that exists in space, as the two boxes and the explosion proves, but the efficiency would be ridiculously poor.  Space travel will become real when we find something that exist in space to act or react against.
I predict that when we do find that element or energy force.... we will blow away the speed of light and when we do that I further predict that we will cause a luminescent boom, the light equivalent of the sonic boom. Inverting light.

The only way I see us getting to the moon is if we fired a missile with enough momentum to leave our atmosphere, with the exact velocity and with the right timing (trial and error) so that a straight path would simple hit the moon.  I’ll bet that in less then five tries we could do it.  To get back we would use current rocket technology but with the moon itself as resistance blast off on a straight path back to earth.  That would be tricky as the only method of hitting the earth would be to use the exact amount of thrust against the moon to accelerate the rocket to a speed that would cause it’s timing and velocity to hit the earth.
we would only have a short distance to accelerate against the moon as there probably is no atmosphere there I don't know, but it wouldn't take much as there is no resistance holding it back.
Robert

#### aasimz

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##### Re: thrust does not work in space
« Reply #110 on: 21/08/2014 15:31:33 »
Ok, I will try to elaborate more on how we don't need an atmosphere to push against.

When you think about it, the gas will expand rapidly from a single point at the centre of the box, when the first atoms reach the sides of the box they are pushed by the atoms behind them and forced to push into the sides, you can consider the centre point as an anchored point in space as the sparks continues. so, it is the gas pushing against it self, if the fuel reaction generated enough force it will explode the box in order to spread in all directions equally, even if one of the sides was open.

The gas will expand the same no matter where it was in the universe.

As for your concerns about the efficiency, well it is not poor as you think at all, considering the gravitation pull at the opposite direction, just like earlier mentioned the amount of the fuel used only to get out from earth atmosphere is much more than the amount used to travel much greater distances out of gravitational fields and out of atmosphere.

If a dynamite explosion took place in space beside you, aren't you going to be effected by this explosion, yes and you will be effected more -by the same dynamite force- than if you were in earth, it will be a stronger effect and you will gain more acceleration than in earth with the same propulsion force, because there is no gravitational mass, and there is no resistance against you, and no atmospheric resistance against the expanding gas. The dynamite explosion will generate the same force always anywhere.
« Last Edit: 23/08/2014 16:54:35 by aasimz »

#### alancalverd

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##### Re: thrust does not work in space
« Reply #111 on: 21/08/2014 23:40:24 »

As the gun barrel has little to nothing in common with the rocket engine, which is to say that the rocket has no projectile to produce backpressure and thus propulsion, I have to maintain that I am not convinced sorry. No disrespect intended and I am very willing to listen.

As far as the physics is concerned, they are identical. The rocket's "projectile" is the exhaust gas molecules.

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I do believe that the kick back in space with the rifle though extremely small and short lived could produce a miniscule amount of propulsion in space.

Alas, belief has no place in science. Nor do words like "extremely" and "minuscule" - physics is about numbers, not adjectives. Conservation of momentum, however, seems to apply throughout the observable universe, and the numbers add up with sufficient accuracy to allow us to walk, fly, and travel to the planets.
helping to stem the tide of ignorance

#### Reality207

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##### Re: thrust does not work in space
« Reply #112 on: 22/08/2014 13:57:17 »
alancalverd - Again thank you for your scientific response.

I agree that the potential energy/force of an explosion/fuel will always be the same; simply put “it is what it is”.  But I ask respectfully; doesn’t the resulting action or reaction totally depend on the environment?

Being 20 feet from an exploded stick of dynamite in atmosphere would hurt.
Everything between one and the explosion would strike one and likely cause one to be knocked over while being “peppered” with the material wrapped around the dynamite and all the material in the atmosphere.  As atmosphere is easily compressed one would have area to be trusted into, resulting in minimal damage.

Being 20 feet from an exploded stick of dynamite in water would be fatal.
Everything between one and the explosion would be trusted toward one but as water cannot be compressed one would have nowhere to go and would be crushed by the pressure of the expansion.

Being 20 feet from an exploded stick of dynamite in space??
Everything between one and the explosion again would be trusted towards one, as there is nothing (we know of) in space, one would only be hit by the wrapping of the dynamite and the particles of the dynamite itself, resulting in the least amount of damage.  As an object in motion tends to stay in motion…. And energy cannot be created or destroyed only transformed the flying particles striking one would cause one to be acted upon, resulting in movement or thrust in space. The result is that one would be hurled endlessly across the universe at the same speed one was accelerated to.
You are gaining in convincing me; however many elements still remain in question.
Sorry time has come that I must depart; please, I will return and I dearly look forward your thoughts.

#### aasimz

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##### Re: thrust does not work in space
« Reply #113 on: 22/08/2014 18:20:14 »
Why would you worry about injury or the material that was wrapping the dynamite and other details, forget all that, we are talking about the force that has been unleashed.

Underwater, as a result of water resistance you will get the least momentum out of that force. Through air a greater momentum. In space it will be the greatest of all, not only because there is no atmospheric resistance but also the non-presence of gravitational effect.

#### alancalverd

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##### Re: thrust does not work in space
« Reply #114 on: 22/08/2014 19:39:06 »

I agree that the potential energy/force of an explosion/fuel will always be the same; simply put “it is what it is”.  But I ask respectfully; doesn’t the resulting action or reaction totally depend on the environment?

First, you must learn the meaning of the technical words you use. Energy, force, momentum and power are all quite different things and whilst you use terms like "energy/force" you will not be thinking clearly enough to follow the physics.

I suggest you learn the definition of momentum and the principle of conservation of momentum before continuing this discussion. Indeed once you have done so, you will immediately see why rockets work in space!

A great deal of the public misunderstanding of science is due to the imprecise use of language.

In the case of a rocket engine, the engine is the environment.
helping to stem the tide of ignorance

#### jeffreyH

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##### Re: thrust does not work in space
« Reply #115 on: 22/08/2014 21:06:35 »
What is pushing are the energetic particles of fuel that are expanding in all directions. I have only read the last page of this thread but find it reasonable that people have problems with this. We think of a push as having to have two elements simply because we as humans have to brace against something to push. If you were to throw 1000 rocks simultaneously at object it will move. The rocks have left the hands before they start to move the object so where is the push backwards? It is the recoil of the rocks from the surface of the object being moved as per Newton.

#### Reality207

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##### Re: thrust does not work in space
« Reply #116 on: 24/08/2014 17:01:07 »
I cut and pasted from alencalvard's thread

"Have you ever fired a rifle? The recoil force is exactly the same whether you fire it under water or in air. Recoil force is independent of the surrounding medium."

I couldn't disagree more Sir ( I hope I am allowed to do that without angering you or anyone else)
Maybe we are having a language break down??  Please correct the science, not the language.
I see the environment has everything to do with the reaction or kick back.

The potential force does not change in different environments!  but the result has to change in different environments, as part of the result has to be influenced by the environment.
Gun powder is gun power in any environment and it's potential will be the same I agree (potential f=ma) but resulting force or kick back when it's energy is released will never be the same in different environment. Everything it touches or that touches it will effect it and if nothing touches it nothing will affect it.
I realize this may upset many but kick back = ma/r   r being the environment which is the resistance.  The resistance of water is much different then the resistance of air.
Run through water then run through air,  your potential MA doesn't change but everyting does.

"what you push against must push back" push against water then push against air, air will compress and not push back much, water does not compress and will push back alot.  push against space and nothing pushes back as there is not (I don't know what I'm missing here??)
I have written lenghty explinations of this that can easily be done here on earth, here's another.

A rifle with a completely sawed off barrel, fired in water, with no projectile, will still have a great amount of resistance as the gasses will try to press into the water that cannot be compressed causing a pill up of the gass, back pressure and a considerable kick back.
A rifle with a completely sawed off barrel, fired in air, with no projectile, will have almost no resistance as air compresses very easily, there is almost no pill up and almost no back pressure and the kick back will be almost nothing.  KB =MA/R.   KB = kick back
thus environment changes forces in action or the kick back, How can you not agree !!!! ?

Maybe we are having a language problem here so please try to understand the thoughts, as perhaps I don't speak your language hopefully you can speak mine.

The dynamic of every atom, every molicule.... has to change when the environmet is changed, as the action and reaction of each one of them is effected differently in different environments. Come on, seriously!!!!

A rifle with a completely sawed off barrel, fired in space, with no projectile, will have no resistance at all and the rifle cannot have any kick back at all, as there is nothing there to act against it.
"Everything you push against must push back", does not and can not apply, as when you push against nothing the law becomes invalid. sorry but .... think about it!!! 0 x 10K = 0
This third scenario to me would most seem to resemble the rocket engine and why I must still conclude that it should have no thrust in space.

I hope I am allowed to have and share my thoughts and opinions, logic and views, even if they are different.  I intend NO DISRESPECT to anyone!!!!  These are simply my views.

Alen, if you are still reading this. sorry I was away, unavoidable; would you please explain what you intend when you wrote, "the engine is the environment"?

--------------------

It seems we are going round and round, but if anyone is willing to explain where the resistance comes from or why it is not needed, I am willing to listen.

Question – what do we know of that actually exists in space? Like radiation, gravity….?

--------------------

On a different subject, as this is getting old...
It is my understanding that the current belief is that, water displaced from the front of a submarine is pushed to the back of the submarine.  There was an experiment where they ejected ink from the front of a submarine and watched as the submarine moved through the ink and the ink fell in behind the submarine.
Is this the general consensus?
Because I have an interesting experiment to share on that, if anyone is interested?

“It is the blend of science and art that leads us to creativity and progress.” rl

#### Reality207

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##### Re: thrust does not work in space
« Reply #117 on: 24/08/2014 17:45:56 »
aasimz wrote
"The gas will expand the same no matter where it was in the universe."

The gas will have the same potential to expand anywhere in the universe.  But as everything it touches and that touches it during expansion, in different environments, will be different, the resulting reaction will be different, everywhere, and so the expansion has to be different!

Contain expanding gas in a rigid box then , then contain the same expanding gas in a balloon
two very different reactions will accure.  am I missing someting in what you are saying in the above quote?

The environment will always affect the action and the reaction.

#### Reality207

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##### Re: thrust does not work in space
« Reply #118 on: 24/08/2014 17:51:32 »
aaismz wrote
Underwater, as a result of water resistance you will get the least momentum out of that force. Through air a greater momentum. In space it will be the greatest of all, not only because there is no atmospheric resistance but also the non-presence of gravitational effect.

We must be having a language thing as that is exactly what I have said, except you correctly add gravity.

My question remains, "how the thrust occurs in space that results in that momentum"?

#### Reality207

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##### Re: thrust does not work in space
« Reply #119 on: 24/08/2014 17:58:49 »
aasimz also wrote,
When you think about it, the gas will expand rapidly from a single point at the centre of the box, when the first atoms reach the sides of the box they are pushed by the atoms behind them and forced to push into the sides, you can consider the centre point as an anchored point in space as the sparks continues. so, it is the gas pushing against it self, if the fuel reaction generated enough force it will explode the box in order to spread in all directions equally, even if one of the sides was open.

that is all true, but again if the first of the expanding gas doesn't strike anything, like in space where there is nothing push back against it continues indefinately and the explination would seem to become invalid.
Sorry I am not trying to be combative, only logical. Perhaps I am missing something?

#### Reality207

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##### Re: thrust does not work in space
« Reply #120 on: 24/08/2014 18:34:13 »
Jeff wrote,
"If you were to throw 1000 rocks simultaneously at object it will move. The rocks have left the hands before they start to move the object so where is the push backwards? It is the recoil of the rocks from the surobjeface of the object being moved as per Newton."

In your analogy the hand represents the rocket and the rock represents the out gas or expanding gasses if I understand your analogy.
In space there is no object for the thrown rocks to strike, so the thrown rock will continue indefinately, there is no recoil, and the hand will see no return thrust; just like I see the rocket in space, no thrust.
Im sorry if my view seem to be anything but respectful, I am not intending to be argumentitive but this analogy doesn't work for me.

Thank you for your understanding of my questions. and thank you for your attemp the help me understand this, but I still don't understand it.

#### aasimz

• Jr. Member
• 42
##### Re: thrust does not work in space
« Reply #121 on: 25/08/2014 00:31:09 »

In your analogy the hand represents the rocket and the rock represents the out gas or expanding gasses

No the hand is what releases the gas, and the rocks are the gas particles and the object is the rocket. And the recoil happens for the gas particles exactly as for rocks and according to Newton's law.
« Last Edit: 25/08/2014 00:32:43 by aasimz »

#### alancalverd

• Global Moderator
• Neilep Level Member
• 4810
• life is too short to drink instant coffee
##### Re: thrust does not work in space
« Reply #122 on: 25/08/2014 07:33:35 »
My question remains, "how the thrust occurs in space that results in that momentum"?

Back to front reasoning.

Start with a rocket in space, not moving. The total momentum of rocket (mass M) plus fuel (mass m) is zero. Now expel the fuel as exhaust gas at velocity v. Since the total momentum must be conserved, mv = -Mv' where /v'/ is the speed of the rocket. The minus sign is there because v and v' are vectors with opposite directions.

If the initial potential energy of the fuel was E than E = (mv2 +Mv'2)/2, from which you can work out the final speed of the rocket - at least in principle: reality is a bit more complicated* because the mass of the rocket plus residual fuel is changing throughout the burn, and some of E is lost heating the rocket engine, but you get the general idea.

Thrust is the result of conservation of momentum - nothing more or less.

*rocket science is dead easy - in fact it's all in these two equations - but rocket engineering is a lot more difficult!
« Last Edit: 25/08/2014 07:40:27 by alancalverd »
helping to stem the tide of ignorance

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #123 on: 25/08/2014 11:23:10 »
Jeff wrote,
No the hand is what releases the gas, and the rocks are the gas particles and the object is the rocket. And the recoil happens for the gas particles exactly as for rocks and according to Newton's law.

1. if the hand is what releases the gas it is part of the rocket, how can it be the acting and the acted at the same time?
2. How does the recoil happen from the gas particles? are they not all traveling at the same speed?

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #124 on: 25/08/2014 13:21:25 »
Again it is really great that you take the time to try to explain this, Thank you, all.

E is obvious, M and m are obvious, but the equation doesn’t explain how in the physical world, the rocket attains V?   Equations, formulas and theories are not going to convince me.

If rockets work in space, (and I’m not saying they do or don’t, just that I don’t see how), it could be explained using actual parts and product, their actions and reactions, by and to particles and substances.     Couldn’t it??

#### alancalverd

• Global Moderator
• Neilep Level Member
• 4810
• life is too short to drink instant coffee
##### Re: thrust does not work in space
« Reply #125 on: 25/08/2014 14:32:03 »
Again it is really great that you take the time to try to explain this, Thank you, all.

E is obvious, M and m are obvious, but the equation doesn’t explain how in the physical world, the rocket attains V?   Equations, formulas and theories are not going to convince me.

If rockets work in space, (and I’m not saying they do or don’t, just that I don’t see how), it could be explained using actual parts and product, their actions and reactions, by and to particles and substances.     Couldn’t it??

Momentum is conserved, anywhere and everywhere. Why not in space? Given that, and the definition of momentum (mass x velocity), if we start with M and m stationary and not connected to anything else, then give an impulse to m so that it attains a velocity v, conservation demands that M must move in the opposite direction with velocity -v' such that mv = -Mv'.

You can apply the principle to rocks, particles, cricket balls, planets, anything you fancy. The force pushing the gas out of the back of the rocket produces a reaction force that accelerates the rocket in the opposite direction (Newton). Actual particles and substances used in space travel include steam, oxides of nitrogen, mercury ions, and a whole lot of more exotic molecules depending on the particular job to be done.
helping to stem the tide of ignorance

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #126 on: 25/08/2014 16:58:38 »
Alan wrote, "then give an impulse to m so that it attains a velocity v,"
I understand all that and I agree except for that one little part, I seem to be hung up on again or still,  how is the impulse provided, where does V come from??

Before momentium is conserved, it must be stablished or its just potential, right?

Do submarines interest you?

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #127 on: 25/08/2014 17:12:20 »
I have a propulsion system that will put submarines over a hundred miles an hour.  EASILY
G-Force that will cause one to pass out, move through water like it was air.
On everything that I am, everything that I have,  I guarentee it!

Something like that worth anything $$, to whom? and how would one, "cash it in"? #### jeffreyH • Global Moderator • Neilep Level Member • 4055 • The graviton sucks ##### Re: thrust does not work in space « Reply #128 on: 25/08/2014 19:35:35 » Jeff wrote, "If you were to throw 1000 rocks simultaneously at object it will move. The rocks have left the hands before they start to move the object so where is the push backwards? It is the recoil of the rocks from the surobjeface of the object being moved as per Newton." In your analogy the hand represents the rocket and the rock represents the out gas or expanding gasses if I understand your analogy. In space there is no object for the thrown rocks to strike, so the thrown rock will continue indefinately, there is no recoil, and the hand will see no return thrust; just like I see the rocket in space, no thrust. Im sorry if my view seem to be anything but respectful, I am not intending to be argumentitive but this analogy doesn't work for me. Thank you for your understanding of my questions. and thank you for your attemp the help me understand this, but I still don't understand it. The hand most definitely does not represent the rocket. The hand represents the centre of the explosive release of the gases. The rocket is to be considered a separate system entirely from the ignited gases otherwise you are bootstrapping a system under its own power which is nonsense. The expanding gases push EVERYTHING away from them including the rocket. That is why there is an outlet for the gases AT THE BACK. #### alancalverd • Global Moderator • Neilep Level Member • 4810 • life is too short to drink instant coffee ##### Re: thrust does not work in space « Reply #129 on: 25/08/2014 20:03:07 » Alan wrote, "then give an impulse to m so that it attains a velocity v," I understand all that and I agree except for that one little part, I seem to be hung up on again or still, how is the impulse provided, where does V come from?? The impulse comes from burning fuel. This converts the potential energy of the mass m of fuel into kinetic energy = mv2/2, hence we have m and v, thus the rocket moves at v' so that Mv' balances mv. Quote Before momentium is conserved, it must be stablished or its just potential, right? Sorry, this is meaningless. Momentum is always conserved. You must appreciate the difference between ∂$$\sum\$$mv = 0 (the sum of momentum vectors doesn't change) and ∂$$\sum\$$mv2/2 > 0 (kinetic energy is created from potential energy). Note that v is a vector but v2 is a scalar, which is what it's all about! Quote Do submarines interest you? only as targets. helping to stem the tide of ignorance #### alancalverd • Global Moderator • Neilep Level Member • 4810 • life is too short to drink instant coffee ##### Re: thrust does not work in space « Reply #130 on: 25/08/2014 20:05:00 » I have a propulsion system that will put submarines over a hundred miles an hour. EASILY G-Force that will cause one to pass out, move through water like it was air. On everything that I am, everything that I have, I guarentee it! Something like that worth anything$$, to whom? and how would one, "cash it in"?

I think you would need to improve your grasp of elementary physics before presenting it to a potential customer.
helping to stem the tide of ignorance

#### dlorde

• Neilep Level Member
• 1441
• ex human-biologist & software developer
##### Re: thrust does not work in space
« Reply #131 on: 26/08/2014 00:19:18 »
An ice rink is a good place to get an understanding of these concepts because of the low friction. If you are standing still holding another person and you push them away, they will move away in one direction and you will move in the opposite direction. If you're holding a shopping trolley full of rocks and start throwing them away, one by one, in the same direction, you will get a small impetus in the opposite direction for each rock you throw. The more rocks you throw, the faster you will go. The rocks don't have to hit anything. If you use a fire extinguisher, the gas coming out has the same effect as throwing thousands of tiny rocks - you'll also get an impetus in the opposite direction. In a vacuum it will be even more noticeable because of the lack of air resistance to your motion. That's how a rocket works too. Newton's Third Law.

#### PmbPhy

• Neilep Level Member
• 2784
##### Re: thrust does not work in space
« Reply #132 on: 26/08/2014 01:39:47 »
Quote from: Reality207
Jeff wrote,
"If you were to throw 1000 rocks simultaneously at object it will move. The rocks have left the hands before they start to move the object so where is the push backwards? It is the recoil of the rocks from the surobjeface of the object being moved as per Newton."

In your analogy the hand represents the rocket and the rock represents the out gas or expanding gasses if I understand your analogy.
In space there is no object for the thrown rocks to strike, so the thrown rock will continue indefinately, there is no recoil, and the hand will see no return thrust; just like I see the rocket in space, no thrust.
Hi Reality207,

I see that you're back trying to prove that all of NASA and every single physicist who's alive today is wrong, huh?

What you said here is, again, not true at all. In fact all one has to do to demonstrate this oneself is to obtain a skateboard and a heavy stone. Sit down on the skate board and make sure its on a very flat smooth surface. Make sure that you and the skateboard are at rest before you throw the stone. Then throw the stone as hard as you possibly can parallel to the ground. The exact moment the rock leaves your hands the whole system of thrower + skateboard will recoil. You and skateboard won't wait until the rock see if there's something to hit because the rock and skateboard doesn't think. And we can replace you with a strong spring and a remote control.

You see, physicists are pretty darn smart people. When they make a law the first thing they do before stating that something is true is to actually see if it is experimentally first before they make claims. Not one of us is so dumb as to postulate a law with nothing to base it on. Physics students do these experiments in their very first year of study when they start their training in college to get their degree in physics. I'm sure they do the same in high school but it's been so long since I was in high school that I forgot.

I've been reviewing your posts in this thread and one of the things that I've noticed is that you're confusing two kinds of propulsion systems; there are those systems that work by pushing against a medium, such as airplanes and boats, and those that work by Newton's Third Law like rockets and missiles.

Here's a simple way to prove it too. Obtain a vacuum pump which will allow you to pull down a decent vacuum. Then get a large long tube or container which is see-through so that you can watch what's going on inside. Get another very very long PCV pipe and attach the other end to a very large container. This PCV pipe and container will allow the exhaust to be moved away for a few seconds so that you can watch the rocket move. Then get a rocket engine from a place which sells model rockets. Learn how to use them so you don't burn yourself or hurt yourself. With these materials you can construct your own vacuum chamber and watch how right NASA and the rest of us are.

I'm still curious as to how you think Men put corner reflecting mirrors on the Moon or satellites in geosynchronous orbit. Would you care to explain that for us?

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #133 on: 26/08/2014 02:56:07 »
first Thank you for your kind responce.
Now your analogy is completely bogus, as there is something foolish people like me call ATMOSPHERE to resist the ball and allow it to accelerate the person on the skateboard that DOES NOT EXIST IN SPACE.

This evening I read for the first time about EmDrive, this is logical to me foolish as I may seem to you. but no one and that includes you Sir has presented ONE element of logic that explains how rockets can thrust against nothing.

let me look through your big telescope and see the flag, the rovers, the mirror I never hear of.

I have a serious question
I went to the space musium and looked at the lander, and the rover, where did they put the rover to carry it up there?  How did they attach it?  no one at the musium could answer that question, will you?

I'm not saying we didn't go there I'm saying I don't see how, so please do be mean to me as these are fair and reasonable questions.

I'm not trying to offend you, can you say that?

#### PmbPhy

• Neilep Level Member
• 2784
##### Re: thrust does not work in space
« Reply #134 on: 26/08/2014 03:43:53 »
Quote from: Reality207
first Thank you for your kind responce.
Now your analogy is completely bogus,
That's a rude way to express your thought.

Quote from: Reality207
as there is something foolish people like me call ATMOSPHERE to resist the ball and allow it to accelerate the person on the skateboard that DOES NOT EXIST IN SPACE.
Not at all. You totally missed the whole point of the experiment. This was about momentum and you treated it as if it had to do with an interaction with the atmosphere. That's easily proven to be total nonsense. Your assumption means that the ball is acting with the atmosphere and it has nothing to do with momentum. That'd mean that the recoil would be independent of the mass of the ball which is empirically incorrect as experiment demonstrates. The larger the ball the more resistance to air. You can keep the mass the same and adjust the size and that will change how the throwing affects what happens. The idea is to make sure that the stone is so small that atmospheric forces can be ignored. That's why you needed to go to take physics classes, i.e. so you wouldn't keep making such horrible mistakes like this in every single post.

Quote from: Reality207
This evening I read for the first time about EmDrive, this is logical to me foolish as I may seem to you. but no one and that includes you Sir has presented ONE element of logic that explains how rockets can thrust against nothing.
The problem is not with us. The problem is with you. You lack the ability to understand the physics. That's all there is to it. Sometimes that happens but none of them are able to admit it. Your claims are all contrary to both theory and experiment. Countless experiments have been done which you know nothing about which prove that you're wrong a thousand times over. It's not up to us to convince you that the science of physics is wrong. It's up to you to learn it before you can make any judgments about it. So do what so many of us physicists have done and spend a half dozen years in intense study learning why physicists hold to be true what we do. Then you have the right to claim everyone in the world is wrong and you're right.

So! Once again I see that you failed to answer my questions and then expected me to answer yours. That's never going to happen. If you can't be respectful enough to answer a question given to you and you rudely ignore it then there's no way in hell that I'll address yours.
« Last Edit: 26/08/2014 03:55:25 by PmbPhy »

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #135 on: 26/08/2014 04:18:37 »
I am preparing my answers, I have been since that last post, not ignoring anyone
I will post it when I complete it and I am doing so.

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #136 on: 26/08/2014 04:37:22 »
Sorry guys if I let my emotions effect me there, pmbphy is not patient like you other
Gentleman, I noticed that in some of his other response.  And I hope I didn’t say anything to offend you guys, as you really have been very kind and patient trying to explain this to me.  But the analogies on earth with atmosphere just don’t help me understand, as there is no atmosphere in space.  You sit on a chair; the chair pushes back.  Take away the chair; and there is no push back.  Everyone keeps saying Newton’s law I totally agree but how does it apply if there is nothing to push back?  I guess I can understand why I probably up set pmbphy, but that is not my intention. I’m NOT a conspiracy theorist and I’m not trying to prove anything, sorry if I seem that way.

Sorry pmbphy I let my emotions get to me.
Pmbphy I am a master electrician not a physicist, that’s clear.  But I have a customer that bought a house wired by a physicist and I fix his electrical work all the time, I don’t have the heart to tell the customer to rewire the whole house or how much his work scares me.  So please, I ask you not to be so condescending and mean.  I believe I have the right to ask these questions without getting this attitude.  And I don’t care how much you spent on education, that doesn’t give you the right to insult people who don’t agree with you.

Jeff and Alan wrote something’s I’m going to reread study that I have not absorbed yet and would like to.  Well try anyway lol.  I am also going to try to understand what Pmbphy wrote between the insults.

Alan, I still have emails from ONR where I explained to them about a plow shaped nose tip modification, that would reflect/displace water more efficiently upward, allowing greater speed sighting that displacing water downward is not as easy as displacing it upwards.  and found out recently they are now experimenting on something just like it.  You know what I am implying. But I must be wrong and they must have had it before me. haha
And I take no offence to your answer about my lack of physics, as I know you wouldn’t do that.  Thanks,

EmDrive the future of space travel, love it. I’m an electrician you can probably understand why.

Perhaps I should say,

#### PmbPhy

• Neilep Level Member
• 2784
##### Re: thrust does not work in space
« Reply #137 on: 26/08/2014 21:51:47 »
Reality207 - Let's start from scratch such as the treatment in Classical Mechanics by John R. Taylor which you can download at http://bookzz.org/book/911552/5131aa

Turn to page 85. That's the page where the section entitle 3.2 Rockets starts. It goes from page 85 to page 87. Please study that section and get back to us.
« Last Edit: 26/08/2014 22:03:56 by PmbPhy »

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #138 on: 26/08/2014 22:48:38 »
pmbPhy I will do that.
I am happy to do that.
and Thank You!
ps I was going to me this my last post, I will get back to you.

#### PmbPhy

• Neilep Level Member
• 2784
##### Re: thrust does not work in space
« Reply #139 on: 26/08/2014 22:58:07 »
Quote from: Reality207
Sorry guys if I let my emotions effect me there, pmbphy is not patient like you other Gentleman, I noticed that in some of his other response.
Hi Reality207,
I was upset when I saw you write this. You hardly know me so you have no cause to make such a claim such as this. You might have said something like Pmbphy was being impatient since that shows a particular state of mind whereas pmbphy is not patient says something about a person’s character which takes a while to learn because you have to get to know them.
Quote from: Reality207
Everyone keeps saying Newton’s law I totally agree but how does it apply if there is nothing to push back?
That is quite correct. It’s what led Einstein to general relativity.
Quote from: Reality207
Einstein to his the- I guess I can understand why I probably up set pmbphy, but that is not my intention.
No problem. I’m finally getting to understand you better now. You could be a great deal more intelligent than I thought you were not that I’ve gone back to studying your posts.

Quote from: Reality207
Pmbphy I am a master electrician not a physicist, that’s clear.
This is something we have in common. I started off as an electronics technician and saw that I was capable of doing a hell of a great real more. So I stopped being an electronics technician and went to college, learned math and even though I totally sucked at arithmetic I was wonderful at trigonometry, algebra, geometry, calculus, etc. It’s a good thing I wasn’t married since that would have been a problem.
Quote from: Reality207
I am also going to try to understand what Pmbphy wrote between the insults.
Thank you. I'll try to do the same with you too. Think what happened was that you and a lot of people do, i.e. they confuse negative criticism with insults. Have you ever noticed that yourself?
« Last Edit: 26/08/2014 23:06:42 by PmbPhy »

#### PmbPhy

• Neilep Level Member
• 2784
##### Re: thrust does not work in space
« Reply #140 on: 26/08/2014 23:00:28 »
pmbPhy I will do that.
I am happy to do that.
and Thank You!
ps I was going to me this my last post, I will get back to you.
That's Wonderful my new friend. I see that we're good to go on this then. Great!  []

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #141 on: 27/08/2014 03:30:57 »
Hi guys,
Maybe there is no hope for me [:-'(]

I read John Taylor and he wrote –
Consider the rocket shown in Figure 3.2 with mass m, traveling in the positive x direction (so I can abbreviate vx as just v) and ejecting spent fuel at the exhaust speed
vex relative to the rocket. Since the rocket is ejecting mass, the rocket's mass m is
steadily decreasing. At time t, the momentum is P(t) = my. A short time later at
t dt, the rocket's mass is (m + dm), where dm is negative, and its momentum is
(m + dm)(v dv). The fuel ejected in the time dt has mass (—dm) and velocity

All I get is, “the rocket is lighter because of repelling fuel and being lighter will allow it to go faster.” Sorry, Am I missing something?
Also, I don’t understand or he didn't include, how the rocket in his explanation got moving in the first place?

John Taylor wrote - “when you push one way on the boot, the boot pushes in the opposite direction on you.”  I don’t understand that, sorry (and I almost want to tremble to say this) I don’t see just the boot pushing as JT states.  The boot and the arm in motion push against the atmosphere and the atmosphere pushes back against the boot and the arm.  Doesn’t it??
Aren’t the atmosphere, the boot, and the hand in motion are an example of Conservation of Motion all acting together?
How come JT doesn’t mention atmosphere?  It must be me???

I hope this is not inappropriate both personally and to the host, but I am going to take a chance (I probably can't sound crazier then I do) and make a Proposition.

I have a feeling you guys PmbPhy, Alan, Jeff, and Dlorde know people with real money, maybe even yourselves.?
I really do have a submarine hull design that will go over a hundred mph do spins, flips, like a roller coater... move through water like a knife in soft butter.
I know how crazy this must sound but I also have a sub design that will do over a thousand mph.  However like a dragster, it will not steer well, its speed will only be limited by HP.
I have a design for the fastest aircraft hull.  It will go as fast as any propulsion system will take it, in our atmosphere, No more nose tip resistance!  Look at me the guy who’s always talking about atmosphere, haha.

I am willing to put everything I own, "put my money where my mouth is."
If you guys can get me/us in front of an investor(s) we can trust.

Terms  to protect everyone:
1. we agree on a price for each and terms:
2. the money, my assets and terms go into a closing company:
3. you bring existing designs to protect me, but don’t show me:
4. I share my new design, we go over them.... and they work or I loose.
5. if my designs already exist (they don't or they would be using them) - show me the designs exit, and I loose. There is no exposure showing me, as I already know the design.
6. we build them, share the money.
Nothing to loose (x-time) and everything to gain.

Or we can figure something out and let Alan make the presentations.
Or tell me if there is a better way, I will share it with you.
I don't have a lot of time left in my life, I'm laying it out, I have a daughter in college with student loans..... enough said.

#### RD

• Neilep Level Member
• 8169
##### Re: thrust does not work in space
« Reply #142 on: 27/08/2014 10:09:50 »
... I know how crazy this must sound but I also have a sub design that will do over a thousand mph.

[hydrodynamic] drag is proportional to the square of the velocity ... http://en.wikipedia.org/wiki/Drag_equation
i.e. to double the speed you have to quadruple the engine power.

Current submarines can do 40 mph submerged, so to do 1000 mph the engine would have to be 625x more powerful , 625x bigger , ( that's more engine than sub) , with 625x current fuel consumption.

So a 1000mph sub is unfeasible.

If you're thinking of using bubbles to reduce hull drag, someone has beat you to it ...

http://en.wikipedia.org/wiki/Supercavitation

« Last Edit: 27/08/2014 10:49:37 by RD »

#### alancalverd

• Global Moderator
• Neilep Level Member
• 4810
• life is too short to drink instant coffee
##### Re: thrust does not work in space
« Reply #143 on: 27/08/2014 11:08:43 »

I am willing to put everything I own, "put my money where my mouth is."
If you guys can get me/us in front of an investor(s) we can trust.

Do you have a patent on your designs? If you have, we can discuss them openly. If not, they are of no interest to an investor.

Be aware that patent examiners do know a lot about classical physics. There was this young lad in the Swiss patent office called Albert Onestone or something...
helping to stem the tide of ignorance

#### PmbPhy

• Neilep Level Member
• 2784
##### Re: thrust does not work in space
« Reply #144 on: 27/08/2014 12:53:10 »
Quote from: Reality207
I have a feeling you guys PmbPhy, Alan, Jeff, and Dlorde know people with real money, maybe even yourselves.?
You couldn’t have been more wrong.
Quote from: Reality207
I really do have a submarine hull design that will go over a hundred mph do spins, flips, like a roller coater... move through water like a knife in soft butter.
So? Contact the Navy and talk to them.
Quote from: Reality207
I know how crazy this must sound ..
Very much so. Especially I see no way to believe that you already built a life size mockup.
Quote from: Reality207
but I also have a sub design that will do over a thousand mph.
How do you know that? From what I’ve seen so far of your understanding of physics you don’t have the ability to design such a hull or predict the performance of a hull design.

More on your efforts to claim why Taylor's section on Rockets. I wanted to correct something in your post so that you might hopefully correct fully it before the next time you post. It has to do with notation. You wrote

Quote
Since the rocket is ejecting mass, the rocket's mass m is steadily decreasing. At time t, the momentum is P(t) = my. A short time later at t dt, the rocket's mass is (m + dm), where dm is negative, and its momentum is (m + dm)(v dv). The fuel ejected in the time dt has mass (—dm) and velocity.
where it should have been written as
Quote
Since the rocket is ejecting mass, the rocket's mass m is steadily decreasing. At time t, the momentum is P(t) = mv. A short time later at t + dt, the rocket's mass is (m + dm), where dm is negative, and its momentum is (m + dm)(v dv). The fuel ejected in the time dt has mass (—dm) and velocity.

It might caused you problems now or later.

Tell me. Have you ever considered what would happen if to massive objects were separated by a compressed spring and the spring was let to expand? What would happen?
« Last Edit: 27/08/2014 15:15:45 by PmbPhy »

#### alancalverd

• Global Moderator
• Neilep Level Member
• 4810
• life is too short to drink instant coffee
##### Re: thrust does not work in space
« Reply #145 on: 27/08/2014 17:38:39 »
helping to stem the tide of ignorance

#### Ethos_

• Neilep Level Member
• 1280
##### Re: thrust does not work in space
« Reply #146 on: 28/08/2014 02:18:35 »
Hi guys,
Maybe there is no hope for me [:-'(]

If you can't understand the following thought experiment, then I'd say there is no hope for you, but alas, I'll give it a try.

Imagine an explosion inside a rocket somewhere out in space. What will happen? The rocket will disintegrate into pieces all traveling away from the origin of blast. If the rocket is symmetrical in design, a sphere, the fragments will depart in a fairly evenly distributed pattern. Now, let's put a nozzle at any point on this object and repeat the experiment. If the structure of the sphere is strong enough, the blast will propel the single object in the opposite direction of the exhaust from the nozzle. And even if the sphere is not strong enough to withstand the blast, the majority of the fragments will still travel in opposite direction of the nozzle.

If you can't understand this simple principle, there is absolutely no hope.
"The more things change, the more they remain the same."

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #147 on: 28/08/2014 03:55:17 »
Has anyone ever tired taking a fast jet as high as it can go and at a speed of 300 mph do a dive and accelerate slowly then at 725mph shut the engine off just before passing out haha and crossing the sound barrier in silence?
I know!  But?
What if you equiped the engine with a rotation resister that would allow it to start slowly and dissipate the sound over a great distance, all you would then have to do is accelerate enough to attain positive propulsion before re-crossing the barrier and go zoom with acceptable boom? HaHa,HaHaHaHa
You sure you don't want to see my design?

#### alancalverd

• Global Moderator
• Neilep Level Member
• 4810
• life is too short to drink instant coffee
##### Re: thrust does not work in space
« Reply #148 on: 28/08/2014 12:43:07 »
The "sound barrier" has nothing to do with the engine. You can see the compression shock wave from a supersonic bullet, a freefalling ballistic missile, or a bomb that exploded a few seconds ago, and you can hear it from the free-spinning propellor of a plane in a steep dive with the engine off.

Happy to look at your designs if they are protected by patent.
helping to stem the tide of ignorance

#### Reality207

• Jr. Member
• 24
##### Re: thrust does not work in space
« Reply #149 on: 29/08/2014 01:46:03 »
happy to do so
can you private message me
provisional patent OK