[Action80]

Imagine some fuel inside a rocket. That fuel has some mass.  The fuel and the rocket have about the same relative velocity.  Now some fuel is inducted into the combustion chamber and combustion starts and the fuel’s energy is released.  The combustion chamber is closed at one end and open at the exhaust end.  Pressure inside the combustion chamber builds up due to the energy released by burning the fuel.   The combusted fuel’s mass is ejected at an accelerated rate out the exhaust end.  Newton’s law would say the accelerated fuel mass would produce an equal and opposite reaction.  That opposite force vector would be in the general direction of the nose of the rocket.


Here is your ‘force pair’.  The mass of the combusted rocket fuel being accelerated toward the exhaust port at the rear of the rocket and the forward part of the combustion chamber attached to the rocket itself.  The rocket’s mass is being accelerated in one direction and the mass of the accelerated fuel in the opposite direction.  The dividing line is the forward part of the combustion chamber as it divides the accelerating mass of the rocket itself in one direction with the accelerating mass of the combusted fuel in the opposite direction.


Any external air pressure at the exhaust end acts like a small back pressure that will slow down the acceleration rate of the exiting combusted fuel a little and reduce the forward acceleration rate of the rocket.  If the rocket is in a vacuum that back pressure will be close to zero and the burned fuel mass will be accelerated at a greater rate.  Everything takes place inside the rocket and the lack of external air has nothing to do with the fuel being accelerated in one direction and the rocket being accelerated in the opposite direction.

The mass of the exhaust is part of the closed system. No force pair can be achieved, as a single closed system cannot pair with itself.

[markjo]

A rocket is a closed system. I haven't ignored the conservation of momentum.

You do understand that a closed system can have more than one component, don't you?  The rocket engine is one component and the propellant is another.  If the propellant is burnt in the combustion chamber causing the exhaust gasses to be accelerated out the back, then what balances the momentum of that accelerated exhaust gas?

Just what is the "relevant work " of a rocket?

It is the exhaust plume (i.e., mass ejected, at an accelerated rate) going in one direction causing the rocket or jet to go in the opposite direction.

What causes the exhaust plume to accelerate in one direction?  Or do exhaust gasses not require a force pair to accelerate?

[Action80]

A rocket is a closed system. I haven't ignored the conservation of momentum.

You do understand that a closed system can have more than one component, don't you?

Relevance? 

The rocket engine is one component and the propellant is another.

Oh, here is the relevance. A statement of something very obvious. Thank you.

If the propellant is burnt in the combustion chamber causing the exhaust gasses to be accelerated out the back, then what balances the momentum of that accelerated exhaust gas?

Exhaust gas goes one direction, rocket goes the other direction.

Jesus, how many times must this be written?

Just what is the "relevant work " of a rocket?

It is the exhaust plume (i.e., mass ejected, at an accelerated rate) going in one direction causing the rocket or jet to go in the opposite direction.

What causes the exhaust plume to accelerate in one direction?  Or do exhaust gasses not require a force pair to accelerate?

Remember the issue you had with the words "monstrous jet of energy..." I do, but let us remind the viewing audience of the rest of asshatted posts now, shall we?

The atmoplane doesn't seem very solid to me.  Wouldn't that "monstrous jet of energy" just push the atmoplane out of its way, especially at higher altitudes where the air is much thinner?

Holy crap! It seems a rocket engine is actually capable of creating a "monstrous jet of energy". Jeez, whoda thunk?

And that "monstrous jet of energy" does indeed displace a significant amount of the atmoplane away, but still the external pressure allows the formation of a plume.   

And yes, a force pair is still required. A closed system cannot form a force pair internal to itself. In the case of both jets and rockets, that force pair can only be formed with an outside environment that has measurable air pressure. The rocket can form a working plume in an environment that has less air pressure than a jet (jets are probably capped at an altitude of of 15 miles or so), probably at around 190,000 ft. or so.

[DuncanDoenitz]

And yes, a force pair is still required. A closed system cannot form a force pair internal to itself. In the case of both jets and rockets, that force pair can only be formed with an outside environment that has measurable air pressure. The rocket can form a working plume in an environment that has less air pressure than a jet (jets are probably capped at an altitude of of 15 miles or so), probably at around 190,000 ft. or so.

Better check again the definition of a Closed System; it is entirely isolated from its environment. 

A rifle cartridge is, and remains, a closed system; bullet goes one way, case and rifle go the other.  Force pair.  Muzzle blast irrelevant.   

A rocket motor is a closed system; combustion gases go one way, motor goes the other.  Force pair.  Plume irrelevant. 

[markjo]

A rocket is a closed system. I haven't ignored the conservation of momentum.

You do understand that a closed system can have more than one component, don't you?

Relevance? 

The rocket engine is one component and the propellant is another.

Oh, here is the relevance. A statement of something very obvious. Thank you.

If the propellant is burnt in the combustion chamber causing the exhaust gasses to be accelerated out the back, then what balances the momentum of that accelerated exhaust gas?

Exhaust gas goes one direction, rocket goes the other direction.

So there is a force pair between the rocket and the exhaust gas?  Glad we have that settled.

Jesus, how many times must this be written?

Until we get this next bit straightened out.

A closed system cannot form a force pair internal to itself. In the case of both jets and rockets, that force pair can only be formed with an outside environment that has measurable air pressure.

Okay, I think that I see the source of your confusion.  You don't seem to understand what "closed system" means.  A closed system does not exchange matter with its surroundings.  That's why it's called a CLOSED system. 

You already agreed that closed systems can have more than one component, therefore you must also agree that force pairs can (and indeed, must) exist within a closed system so that momentum is conserved.

[Action80]

And yes, a force pair is still required. A closed system cannot form a force pair internal to itself. In the case of both jets and rockets, that force pair can only be formed with an outside environment that has measurable air pressure. The rocket can form a working plume in an environment that has less air pressure than a jet (jets are probably capped at an altitude of of 15 miles or so), probably at around 190,000 ft. or so.

Better check again the definition of a Closed System; it is entirely isolated from its environment. 

A rifle cartridge is, and remains, a closed system; bullet goes one way, case and rifle go the other.  Force pair.  Muzzle blast irrelevant.   

A rocket motor is a closed system; combustion gases go one way, motor goes the other.  Force pair.  Plume irrelevant.

A rocket requires nothing outside of it, unlike a jet, to create thrust, ergo, a closed system.
 
I am laughing at the folly you exhibit claiming the muzzle blast has nothing to do with the recoil on a rifle...just plain bullshit. Can you help yourself at all?

A closed system cannot form a force pair with itself.

Stop posting bullshit.

[Action80]

So there is a force pair between the rocket and the exhaust gas?  Glad we have that settled.

The exhaust gas (plume) is part of the rocket. A single system cannot form a force pair with itself.

Okay, I think that I see the source of your confusion.  You don't seem to understand what "closed system" means.  A closed system does not exchange matter with its surroundings.  That's why it's called a CLOSED system. 

You already agreed that closed systems can have more than one component, therefore you must also agree that force pairs can (and indeed, must) exist within a closed system so that momentum is conserved.

I think you are blind to the meaning of the word "exchange."

A rocket does not exchange matter with its surroundings, It only gives matter (i.e., exhaust) to its surroundings. It takes in nothing from its surroundings.

A closed system cannot form a force pair with itself.

The end.

[markjo]

So there is a force pair between the rocket and the exhaust gas?  Glad we have that settled.

The exhaust gas (plume) is part of the rocket. A single system cannot form a force pair with itself.

If there is no force pair, then what causes the exhaust to accelerate in one direction and the rocket to accelerate in the other?

I think you are blind to the meaning of the word "exchange."

A rocket does not exchange matter with its surroundings, It only gives matter (i.e., exhaust) to its surroundings. It takes in nothing from its surroundings.

A closed system cannot form a force pair with itself.

And you are blind to the meaning of the word "closed". 

Propellant from outside the rocket loaded into it and then forcibly ejected back outside of it.

A closed system does not take in matter from from outside of itself or eject matter to the outside of itself.  That would be an open system.

If you must insist that a rocket is a closed system, then you must understand that the rocket engine and the resulting exhaust gasses are 2 elements within that closed system that can and must force pair because momentum must be conserved in a closed system. 

It isn't a case of the closed system force pairing with itself.  It's a case of the force pair happening within the closed system.  A very significant difference that you don't seem to grasp.

[RonJ]

If you wish to define the boundaries of a rocket’s system as the entire universe then that rocket could be considered a closed system.  That would be the only way that rocket could be classified as a closed system because the burning fuel exits the rocket’s chassis and travels off to some unknown place after exiting the nozzle. 
 
The conventional way of classifying systems would be to say that mass never enters or leaves a closed system.  Since a conventional rocket has the mass of its fuel leaving out the nozzle on a continuous basis while the rocket is starting its travels, you would conventionally classify it as an open system. 
 
It would be better for you to define your system boundaries to avoid further confusion about whether a rocket is an open or closed system.   

[Action80]

If there is no force pair, then what causes the exhaust to accelerate in one direction and the rocket to accelerate in the other?

Have you read the thread?

And you are blind to the meaning of the word "closed". 

Propellant from outside the rocket loaded into it and then forcibly ejected back outside of it.

A closed system does not take in matter from from outside of itself or eject matter to the outside of itself.  That would be an open system.

Losing sight of the word, "exchange".

Have you read the thread?

Or are you just going to continue your lying, gaslighting ways?

If you must insist that a rocket is a closed system, then you must understand that the rocket engine and the resulting exhaust gasses are 2 elements within that closed system that can and must force pair because momentum must be conserved in a closed system. 

It isn't a case of the closed system force pairing with itself.  It's a case of the force pair happening within the closed system.  A very significant difference that you don't seem to grasp.

I see.

You are just going to continue to post bullshit and lie your ass off.

[Realestfake]

Losing sight of the word, "exchange".

Have you read the thread?

Or are you just going to continue your lying, gaslighting ways?

If you must insist that a rocket is a closed system, then you must understand that the rocket engine and the resulting exhaust gasses are 2 elements within that closed system that can and must force pair because momentum must be conserved in a closed system. 

It isn't a case of the closed system force pairing with itself.  It's a case of the force pair happening within the closed system.  A very significant difference that you don't seem to grasp.

I see.

You are just going to continue to post bullshit and lie your ass off.

Nobody’s lying to or gaslighting you. You’ve wasted half your breath in this thread telling people to “stop posting bs!” “leave reality to the sane!” instead of anything of real substance.

[Action80]

Nobody’s lying to or gaslighting you. You’ve wasted half your breath in this thread telling people to “stop posting bs!” “leave reality to the sane!” instead of anything of real substance.

Actually, you are lying and gaslighting me again, right now with ^this post.

I have posted the exact method of how rockets and jets work within this thread and numerous times in various other threads on this forum.

All you have posted is a bunch of lying crap, merely demonstrating your ineptitude and inability to read or understand the subject matter of your op, you faker.

[markjo]

If there is no force pair, then what causes the exhaust to accelerate in one direction and the rocket to accelerate in the other?

Have you read the thread?

Sorry, but an exhaust plume force pairing with the ever thinning atmoplane doesn't cut it.  That is unless you can show the math that proves that an ever thinning atmpolane can form a force pair that is sufficient to propel several hundred tons of rocket upwards.

Losing sight of the word, "exchange".

Not at all. 

Two types of exchange can occur between system and surroundings: (1) energy exchange (heat, work, friction, radiation, etc.) and (2) matter exchange (movement of molecules across the boundary of the system and surroundings).

You're the one who seems to be losing sight of the word "closed" as it applies to thermodynamic systems.

Based on the types of exchange which take place or don't take place, we will define three types of systems:

    isolated systems: no exchange of matter or energy
    closed systems: no exchange of matter but some exchange of energy
    open systems: exchange of both matter and energy

Have you read the thread?

Have you read a physics text book?

Or are you just going to continue your lying, gaslighting ways?

No lying or gaslighting.  Just trying to educate you.  Some words can have a somewhat different meaning in physics than in everyday usage, so I suppose that I can see how you might not be able to tell the difference.

But if you insist that I'm lying, then please provide a credible source that disagrees with me and agrees with you.  Citing yourself doesn't count.

[Action80]

Not at all. 

Two types of exchange can occur between system and surroundings: (1) energy exchange (heat, work, friction, radiation, etc.) and (2) matter exchange (movement of molecules across the boundary of the system and surroundings).

You're the one who seems to be losing sight of the word "closed" as it applies to thermodynamic systems.

Absolutely gaslighting again.

An exchange is where 1 system provides something to a 2nd system in exchange for something the 2nd system provided to system 1.

Have you read a physics text book?

Yes.

No lying or gaslighting.  Just trying to educate you.  Some words can have a somewhat different meaning in physics than in everyday usage, so I suppose that I can see how you might not be able to tell the difference.

But if you insist that I'm lying, then please provide a credible source that disagrees with me and agrees with you.  Citing yourself doesn't count.

You are lying and gaslighting. You cannot even comprehend the sources you provide to support your bankrupt position, so providing additional sources would be foolish. You are claiming that a closed system can form a force pair with itself, ffs!

Gtfo with your bs.

[markjo]

Absolutely gaslighting again.

An exchange is where 1 system provides something to a 2nd system in exchange for something the 2nd system provided to system 1.

If we were using the word "exchange" in its everyday usage, then you might be correct.  However, we are (or at least I am) using it in the context of its scientific definition, which does not necessarily imply a 2 way trade.

Either way, you're getting hung up on semantics more than the real point: a closed system, by any scientific definition, does not gain or lose matter.  That's why it's called "closed".

You are lying and gaslighting. You cannot even comprehend the sources you provide to support your bankrupt position, so providing additional sources would be foolish.

So I'm just supposed to take your word for it? 

You are claiming that a closed system can form a force pair with itself, ffs!

No, I am not claiming that.  I am claiming that objects within a closed system can, and must, force pair with each other in order to conserve momentum.  I am claiming that the rocket engine and the exhaust are two of the many objects that make up a closed system rocket and form a force pair that allows the exhaust to accelerate in one direction and the rest of the rocket to accelerate in the opposite direction.

[Dr Van Nostrand]

OK.. Let's try this thought experiment...

There's this dude floating naked in weightless vacuum. He's curled up holding his knees in his arms, floating there, and he has a forceful blast of diarrhea. The particles of fecal matter would give his rectum something to push against with no surrounding atmosphere.
The diarrhea would easily shoot out with forward moment and impinge some momentum to the guy's ass, moving him ever so slightly forward.  In fact, if the blast of diarrhea had enough force and volume, it could act as a directional thruster, like on an orbital satellite.

Even if you want to insist that no movement occurred, imagine that you are in a microscopic submarine riding in the dude's colon when he blasted out the diarrhea. Your tiny sub would become a space ship and ride on a wave of diarrhea at sub-relativistic speeds to reach the next star system in 100,000 years.

This is basic science.

[Action80]

If we were using the word "exchange" in its everyday usage, then you might be correct.  However, we are (or at least I am) using it in the context of its scientific definition, which does not necessarily imply a 2 way trade.

Either way, you're getting hung up on semantics more than the real point: a closed system, by any scientific definition, does not gain or lose matter.  That's why it's called "closed".

Exchange means exactly that. Exchange. A closed system can lose matter.

You are lying and gaslighting. You cannot even comprehend the sources you provide to support your bankrupt position, so providing additional sources would be foolish.

So I'm just supposed to take your word for it? 

Doesn't matter to me whether you take my word for it or not.

You have been called out for it by the moderation here at this site, numerous times, being relegated to Purgatory for an extended period for exactly that.

You are claiming that a closed system can form a force pair with itself, ffs!

No, I am not claiming that.  I am claiming that objects within a closed system can, and must, force pair with each other in order to conserve momentum.  I am claiming that the rocket engine and the exhaust are two of the many objects that make up a closed system rocket and form a force pair that allows the exhaust to accelerate in one direction and the rest of the rocket to accelerate in the opposite direction.

BWHAHAHAHA! In other words, "No, I am not claiming that, but let me restate that claim here in direct response."

GTFO...

[DuncanDoenitz]

@Action80.  A system can comprise several entities.  For example the Joule Experiment, which you sometimes quote, comprises a cylinder, a gas, and (depending on the form used) a piston.  All Markjo is suggesting, and which you apparently find derisible, is that some of these components within the sysem can form a force-pair.  The system as a whole is not "acting against itself", but 2 independant entities within the CLOSED system acting against each other.   

Whilst I'm here, can I ask what you believe the nature of the "plume" to be?  By that, I mean is it a gas, does it have substance, does it have mass?  Would you agree that it is formed from the exhaust material of the rocket motor?  Would you agree that, as it is constantly being generated by the motor, that it must be dispersing at an equal rate?  Where is it going? 

Finally, and this is not part of the debate though it's something another couple of people have mentioned; I've no idea of your education level, nor indeed of any of the correspondents on this thread with the possible exception of RonJ who, like myself, says he is a Licensed Aircraft Maintenance Technician.  What I believe, however, is that everyone debating with you is expressing genuinely held opinions.  Some people may have misunderstood what they have learnt, and everyone seems to have misread what you have written, to the extent that we talk BS, make false claims, lie, strawman and gaslight.  You, on the other hand, are a paragon of truth, despite making repeated claims about the voracity of the "plume" thing, and how it is widely accepted by jet engine manufacturers and your nephew (though entirely without any citations to that effect).  I wonder if the disrespect and aggression shown in your replies is founded in a lack of confidence in your stated opinions. 

Without exception I, and the other correspondents, have treated you with utmost respect.  Like a closed system, it would be nice if this were recipricated. 

[markjo]

A closed system can lose matter.

No, it cannot.  That's why it's called a closed system.  You're thinking of an open system.  If you don't believe me, then let's ask Professor Google:
 https://letmegooglethat.com/?q=can+a+closed+system+lose+matter

Of course you won't believe the internet either because it uses the word "exchange" in reference to matter entering or leaving a system.  Maybe this video will help:

BWHAHAHAHA! In other words, "No, I am not claiming that, but let me restate that claim here in direct response."

*sigh*  Okay, so you don't understand the difference between "with" and "within" either.  Here's a hint: "within" means "inside".  So when I say that objects can force pair within a closed system, I mean that objects can force pair inside a closed system.  Does that help?

[Action80]

@Action80.  A system can comprise several entities.  For example the Joule Experiment, which you sometimes quote, comprises a cylinder, a gas, and (depending on the form used) a piston.  All Markjo is suggesting, and which you apparently find derisible, is that some of these components within the sysem can form a force-pair.  The system as a whole is not "acting against itself", but 2 independant entities within the CLOSED system acting against each other.

More cosigning of the gaslighting. Since you guys like this site so much: https://physics.stackexchange.com/questions/419854/why-an-internal-force-cannot-move-a-closed-system-externally

You guys have been claiming over and over again the combusted gas does the work of moving the rocket inside the combustion chamber, which is just pure bullshit.

A closed system cannot form a force with itself.

Whilst I'm here, can I ask what you believe the nature of the "plume" to be?  By that, I mean is it a gas, does it have substance, does it have mass?  Would you agree that it is formed from the exhaust material of the rocket motor?  Would you agree that, as it is constantly being generated by the motor, that it must be dispersing at an equal rate?  Where is it going?

Of course the plume is exhausted gas.  Of course it is being dispersed out the back at a set rate governed by the exhaust nozzle. 

Remember just a day or so ago when you made the asshatted claim that the muzzle blast has nothing to do with the recoil on a rifle, shotgun, etc.? I mean, I cannot believe you made such an obviously stupid claim, but here it is again in all its wonder:

A rifle cartridge is, and remains, a closed system; bullet goes one way, case and rifle go the other.  Force pair.  Muzzle blast irrelevant.   

Aside from being a stupid claim, let's examine what happens when you happen to put a brake on: https://www.silencercentral.com/blog/how-much-does-muzzle-brake-reduce-recoil/#:~:text=A%20muzzle%20brake%20is%20a,the%20muzzle%20behind%20a%20bullet.
If you read that information you will see what happens when you diffuse the escaping gas (i.e., muzzle blast) on the end of the barrel. Recoil is reduced.

When gas is released to vacuum, guess what happens to that gas? Ah, yes...it becomes absolutely diffused! No ability for an opposite reaction to occur.

Finally, and this is not part of the debate though it's something another couple of people have mentioned; I've no idea of your education level, nor indeed of any of the correspondents on this thread with the possible exception of RonJ who, like myself, says he is a Licensed Aircraft Maintenance Technician.  What I believe, however, is that everyone debating with you is expressing genuinely held opinions.

When the opinion is baseless and without merit, I do not care. I will call it bullshit and state very clearly why it is bullshit. 

Some people may have misunderstood what they have learnt, and everyone seems to have misread what you have written, to the extent that we talk BS, make false claims, lie, strawman and gaslight.  You, on the other hand, are a paragon of truth, despite making repeated claims about the voracity of the "plume" thing, and how it is widely accepted by jet engine manufacturers and your nephew (though entirely without any citations to that effect).   

Without exception I, and the other correspondents, have treated you with utmost respect.  Like a closed system, it would be nice if this were recipricated.

I guess "treating others with respect," must entail making false claims about how jets and rockets accomplish motion, and rifles experience recoil.

I wonder if the disrespect and aggression shown in your replies is founded in a lack of confidence in your stated opinions.

Calling out obvious bullshit, lying, and gaslighting is absolutely, totally, 100 percent ! ! !, respectful behavior.

I do not care whether you like it or not.