[totallackey]

So nice to have you back

Gas flowing in a tube is isentropic only in the case of ideal fluid flow.

Also, sound can travel in a vacuum. Any detonation, like a supernovae, sends a shock front.

These are fairly basic concepts many study in college.

Sound has nothing to do with the issue of propulsion.

Isentropic process of gas flowing in a tube has nothing to do with propulsion.

You got it! Finally.

None of these things has to do with propulsion.

Conservation of momentum is what creates the propulsion.

If you fart in space, you move in the opposite direction to your fart plume.

It took a while, but we got there!

If the space you were in wasn't a vacuum, yes, you are correct.

Gas released in to or in a vacuum has never done work and never will do work.

Moving in the opposite direction of gas released has nothing to do with the conservation of momentum.

Go discuss your mythical ramblings elsewhere.

[totallackey]

Despite quoting it, you skipped the part explaining, why those videos show no valid prove of rockets not working in a vacuum.
Fine with me, I'll accept it as tacit agreement.

Just like everything else you have written in this thread, that would be wrong too.

The delay you see when rockets launch on TV (i.e., the government or private industry launches) is due to the fact that the plume is not yet contained enough by the surrounding pressure in order for the rocket to take flight.

How about this explanation:
A rocket engine (like many engines) needs a certain time to get up to full working power.
While the thrust provides less acceleration than gravitation (or UA if one leans that way) working the other way, the rocket remains stationary.
Then acceleration will be very slow, but increasing until the rocket engine provides constant acceleration (depending on the rocket engine, that might be adjustable, but for take-off it's reasonable to assume constant full thrust).
The observable result would be a delay until somethings happens, then slow and finally constant acceleration.

On the other hand:
How can a gaseous atmosphere "contain" a plume?
The atmosphere will do some "shaping", as it is being displaced by exhaust, but that effect quickly evens out, as the amount of exhaust is rather insignificant in comparison to the amount of atmosphere surrounding it.
The exhaust is expelled at speed and will be slowed done by the resistance of the surrounding atmosphere. At the same time it will dissipate, as exhaust and atmosphere mix.
Impressive to look at, but irrelevant for propulsion. Pushing yourself off "thin air" doesn't work much better than pushing yourself off a vacuum.
Rockets work in any environment, because they do neither.

It is the evening out that is necessary to deefine the plume.
 

This does not apply to model rockets of course, because the weight is not sufficient enough to require it.

Why are you making a special case for model rockets?[/quote]
Because the only delay found for model rockets to liftoff is the fuel to ignite.

Once the fuel is ignited, the rocket is off the pad.
 

The described isentropic flow through the nozzle applies to sound and has nothing to do with propulsion.

Why would isentropic flow through the nozzle have anything to do with sound? It is about thermodynamics not acoustics. The speed of sound is relevant, but not sound as such.
In contrast isentropic flow is relevant to work being done, so it is relevant to propulsion.

iC

The article posted refers only to sound in reference to the activity at the nozzle.

The flow of gas into a vacuum is non-isentropic.

The flow of gas coming from an exhaust of a rocket, supposedly in outer space, is taking place in a vacuum.

Non-isentropic.

Hence the jibber jabber, ridiculous double speak in the source provided by stack...

[BRrollin]

So nice to have you back

Gas flowing in a tube is isentropic only in the case of ideal fluid flow.

Also, sound can travel in a vacuum. Any detonation, like a supernovae, sends a shock front.

These are fairly basic concepts many study in college.

Sound has nothing to do with the issue of propulsion.

Isentropic process of gas flowing in a tube has nothing to do with propulsion.

You got it! Finally.

None of these things has to do with propulsion.

Conservation of momentum is what creates the propulsion.

If you fart in space, you move in the opposite direction to your fart plume.

It took a while, but we got there!

If the space you were in wasn't a vacuum, yes, you are correct.

Gas released in to or in a vacuum has never done work and never will do work.

Moving in the opposite direction of gas released has nothing to do with the conservation of momentum.

Go discuss your mythical ramblings elsewhere.

Well of course it does! That is the simplest case of conservation of momentum you first learn: Mv_1=-mv_2. Don’t get much easier than that!

Well once the gas is released, it’s no longer a vacuum now is it?

[iCare]

Despite quoting it, you skipped the part explaining, why those videos show no valid prove of rockets not working in a vacuum.
Fine with me, I'll accept it as tacit agreement.

Just like everything else you have written in this thread, that would be wrong too.

Obviously assuming "tacit agreement" would have been wrong - hence the " ".
In contrast, most of what I have posted in this thread has been correct.
Not everything, as I recalled some (non-critical) details incorrectly, but - as mentioned before - part of why I enjoy this discussion is because I can refine my understanding of the issue.

It is the evening out that is necessary to deefine the plume.
Once the fuel is ignited, the rocket is off the pad.

Doesn't to even something out mean to make it even all over. In this case pressure/exhaust/surrounding atmosphere will interact till there is no pressure differential.
Defining a plume on the other hand should mean to have a distinct plume separated from the atmosphere. That certainly doesn't sound like evening out.
 

Because the only delay found for model rockets to liftoff is the fuel to ignite.

I've started small rockets myself and seen others do it and my observations differ.
The fuel ignites, there is visible exhaust and a delay before the small rockets take off.
As small rockets do have a different mass/thrust ratio (in addition to other differences) that delay may be so short as to appear nonexistent to you.

The article posted refers only to sound in reference to the activity at the nozzle.

Please, do read the reference again. I just did and it does not refer to sound, but to the speed of sound and the velocity of the flow in relation to it.
Which part of the source does refer to sound in your opinion?

The flow of gas into a vacuum is non-isentropic.
The flow of gas coming from an exhaust of a rocket, supposedly in outer space, is taking place in a vacuum.
Non-isentropic.

And non-relevant.
As you're simply repeating previous claims, please refer to my previous responses why they don't apply.

Hence the jibber jabber, ridiculous double speak in the source provided by stack...

If it sounds like "jibber jabber" to you, that may be because it is or because you do not understand it correctly.
Comparing the source in question (or the one you provided for the closed-system-discussion) to your interpretation of it, I'm leaning towards the latter.

iC

[Dr Van Nostrand]

All the jibber jabber can be boiled down to one simple principle of physics.

If you detonate a hand grenade in a vacuum will the expanding energy and gas do the work of driving the shrapnel in all directions?

Why not?

[stack]

Okay will do!

I’ll probably start with those same articles. They seem to know about it.

Unless you have some other sources about entropy that might help me learn about it in the way you do?

Simply put, entropy is a quantity representing the availability of the thermal energy in a system to be converted into work.

A rocket cannot possibly maintain constant entropy.

Incorrect, as you will see in a moment.

As stack writes falsely:

Rocket engines are considered Isentropic systems where entropy remains unchanged.

Isentropic nozzle flow
"Whenever a gas is forced through a tube, the gaseous molecules are deflected by the tube's walls. If the speed of the gas is much less than the speed of sound, the gas density will remain constant and the velocity of the flow will increase. However, as the speed of the flow approximates the speed of sound, compressibility effects on the gas are to be considered. The density of the gas becomes position dependent. While considering flow through a tube, if the flow is very gradually compressed (i.e. area decreases) and then gradually expanded (i.e. area increases), the flow conditions are restored (i.e. return to its initial position). So, such a process is a reversible process. According to the Second Law of Thermodynamics, whenever there is a reversible and adiabatic flow, constant value of entropy is maintained. Engineers classify this type of flow as an isentropic flow of fluids.”

So you see, a Nonisentropic process, like Free Expansion, does not apply to an Isentropic system. Apples and oranges.

...it is obviously written by someone trying to engage in double speak...

And stack, while he talks of the rocket engine, does NOT want you to look behind the curtain containing the rocket exhaust, which is where the meat and potatoes is at.

A rocket has a fixed amount of fuel and a fixed amount of potential energy.

Rockets have a fixed rate of discharge at any particular point of time.

Sooner or later, there is no more more potential energy available.

Therefore, rockets cannot maintain unchanged entropy when in operation.

And that process is not "reversible," nor can it possibly be "adiabatic," as described in stacks' ridiculous post, once initiated. Rockets experience no reverse flow of fluids or exhaust. The exhaust is supposedly taking place in the vacuum of outer space...again, where all the fakers want you to believe that gas, just because it is coming from a rocket, can somehow, someway...be different...but it, of course...cannot.

Gas released into a vacuum...does no work.

All of what you wrote is false and backed by zero evidence or science. Regarding Rockets and Isentropic Flow:

"As a gas is forced through a tube, the gas molecules are deflected by the walls of the tube. If the speed of the gas is much less than the speed of sound of the gas, the density of the gas remains constant and the velocity of the flow increases. However, as the speed of the flow approaches the speed of sound we must consider compressibility effects on the gas. The density of the gas varies from one location to the next. Considering flow through a tube, as shown in the figure, if the flow is very gradually compressed (area decreases) and then gradually expanded (area increases), the flow conditions return to their original values. We say that such a process is reversible. From a consideration of the second law of thermodynamics, a reversible flow maintains a constant value of entropy. Engineers call this type of flow an isentropic flow; a combination of the Greek word "iso" (same) and entropy."

More information and equations can be found here:
https://www.grc.nasa.gov/WWW/k-12/airplane/isentrop.html

You see, engineers call this type of flow an isentropic flow. You are neither an engineer, nor a rocket scientist, nor an expert in thermodynamics yet you claim to know more than people who are without providing any evidence. Your "free expansion does no work" is nonisentropic and does not apply here to rocket engines, so that argument you originally had is toast.

For once, please provide some evidence for you claims rather than just ignorant unfounded bluster.

For once, understand what the hell you are reading and where the flow is taking place.

I mean, read the whole thing...

And make note of the word TUBE!

Gas...in a...TUBE...

Not gas...in a...nozzle.

Now, goodbye to your lack of understanding.

Just how you never provide evidence you apparently don't read evidence either. Here's the next paragraph after the one the one I cited above:

"Isentropic flows occur when the change in flow variables is small and gradual, such as the ideal flow through the nozzle shown above. The generation of sound waves is an isentropic process. A supersonic flow that is turned while the flow area increases is also isentropic. We call this an isentropic expansion because of the area increase."

Here's the image 'shown above' that it refers to:



You really have to start providing some evidence rather than just jibber-jabber. For once and for all the nonisentropic law of free expansion where gas in a vacuum 'does no work' does not apply to rockets. Rockets are isentropic, period. Read the literature. If you disagree, provide some evidence to back up your claims, not just your own ignorance of the subject.

Holy crap...isentropic relative to the sound?

LOL!

Like, A: Sound could even travel in a vacuum...

The speed of sound is a measurement, approximately 343 m/s. Read up on it.

Yeah, we know...having nothing to do with what you tried to introduce and nothing to do with gas performing no work in a vacuum.

What is has to do with a rocket is that mach is part of the equations used to determine the amount of thrust that is present.



*Note Mach and the isentropic flow equation.

2) Gas does no work when released to a vacuum...

Take your nonsense peddling show elsewhere.

Again, for the umpteenth time, free expansion or, "gas does no work in a vacuum", is in reference to nonisentropic systems. Rockets, as has been shown over and over again, are an isentropic system. If you don't agree then I suggest you bone up on your rocket science curriculum.

When gas is flowing in a tube, isentropic...not relevant to the exhaust.

When sound is emitted as a result of the exhaust, isentropic...not possible for sound to travel in a vacuum...

So, isentropic for both, up to the point when a rocket enters any part of a vacuum.

At that point, the gas flow in the tubes remains isentropic...any gas flow from the nozzle becomes, because of the law of free expansion, becomes freely expanding gas.

Gas that freely expands does no work.

Bye bye now...

Ok, for once can you please provide some scholarly (or even non-scholarly, anything) citations to back up your claims. You're just riffing off the top of your head because you're hung up on Joule's "does no work" schtick mixed with a smattering of confirmation bias and a potent dose of Dunning-Krueger. It doesn't apply here. As has been shown many, many times, 'free expansion' is a nonisentropic process. Rockets are an isentropic process. Apples and oranges. And rockets remain an isentropic process regardless of the medium they are in, sea level or vacuum, because the isentropic process has no bearing or reliance on said medium, with exception of nozzle design, that I'll get to in a minute. Get it? It's rocket science, but not that complex.

This from a Stanford publication, "Rocket Performance and Efficiency":

"0.2 Effective Exhaust Velocity and Specific Impulse
Now that we have covered the basic mechanics of thrust and the isentropic nozzle relations we will begin to show how these apply to rockets by defining a set of convenient parameters.


Followed by a bunch of equations that are used to create such a system that will produce the necessary propulsion/thrust. Read more here:
https://web.stanford.edu/~cantwell/AA103_Course_Material/RocketPerformanceNotes_J_Dyer.pdf

As for nozzle design, they are designed differently for within the atmosphere and for max efficiency in a vacuum as I alluded to before. More from Stanford:



*You'll note the differnt designs for atmospheric operation versus a vacuum. (inset)

Now, for once, provide just a smidge of something to back up your claim that a rocket can't work in a vacuum. Not just spouting 'free expansion - does no work' as it doesn't apply here so that point is moot to the discussion. Find something else to try and back up your claims and cite it.

[totallackey]

So nice to have you back

Gas flowing in a tube is isentropic only in the case of ideal fluid flow.

Also, sound can travel in a vacuum. Any detonation, like a supernovae, sends a shock front.

These are fairly basic concepts many study in college.

Sound has nothing to do with the issue of propulsion.

Isentropic process of gas flowing in a tube has nothing to do with propulsion.

You got it! Finally.

None of these things has to do with propulsion.

Conservation of momentum is what creates the propulsion.

If you fart in space, you move in the opposite direction to your fart plume.

It took a while, but we got there!

If the space you were in wasn't a vacuum, yes, you are correct.

Gas released in to or in a vacuum has never done work and never will do work.

Moving in the opposite direction of gas released has nothing to do with the conservation of momentum.

Go discuss your mythical ramblings elsewhere.

Well of course it does! That is the simplest case of conservation of momentum you first learn: Mv_1=-mv_2. Don’t get much easier than that!

Well once the gas is released, it’s no longer a vacuum now is it?

There are three laws of motion:
1) An object in motion (or at rest) will stay in motion (or at rest) until some outside force acts upon it, or inertia.
2) F= m*a
Since we know that gas does 0 work when released to a vacuum, we know that F must = 0.

Since we know that gas has mass, then m =/= 0.

If m =/= 0, that must mean that a = 0, since the only way to obtain a product of 0 is... either the multiplicand or multiplier must = 0.

[wpeszko]

Since we know that gas does 0 work,

Nope.

[totallackey]

Since we know that gas does 0 work when released to a vacuum,

Nope.

FTFY...

[BRrollin]

So nice to have you back

Gas flowing in a tube is isentropic only in the case of ideal fluid flow.

Also, sound can travel in a vacuum. Any detonation, like a supernovae, sends a shock front.

These are fairly basic concepts many study in college.

Sound has nothing to do with the issue of propulsion.

Isentropic process of gas flowing in a tube has nothing to do with propulsion.

You got it! Finally.

None of these things has to do with propulsion.

Conservation of momentum is what creates the propulsion.

If you fart in space, you move in the opposite direction to your fart plume.

It took a while, but we got there!

If the space you were in wasn't a vacuum, yes, you are correct.

Gas released in to or in a vacuum has never done work and never will do work.

Moving in the opposite direction of gas released has nothing to do with the conservation of momentum.

Go discuss your mythical ramblings elsewhere.

Well of course it does! That is the simplest case of conservation of momentum you first learn: Mv_1=-mv_2. Don’t get much easier than that!

Well once the gas is released, it’s no longer a vacuum now is it?

There are three laws of motion:
1) An object in motion (or at rest) will stay in motion (or at rest) until some outside force acts upon it, or inertia.
2) F= m*a
Since we know that gas does 0 work when released to a vacuum, we know that F must = 0.

Since we know that gas has mass, then m =/= 0.

If m =/= 0, that must mean that a = 0, since the only way to obtain a product of 0 is... either the multiplicand or multiplier must = 0.

Ouch. Okay, a force can exist yet do zero work, so your statement that since there is zero work then the force is zero is simply incorrect.

For example, magnetic forces do no work.

Also, you forgot the relevant law here.

F12=-F21, so
m2a2=-m1a1, thus
m2(dv2/dt)=-m1(dv1/dt), hence
m2v2+m1v1=constant

I’d like to point out that these are the basics. We’re not talking about complicated things, but the first things you learn in college.

The fact that you are mistaken on these basic points makes it difficult to take you seriously.

[iCare]

There are three laws of motion:
1) An object in motion (or at rest) will stay in motion (or at rest) until some outside force acts upon it, or inertia.
2) F= m*a
Since we know that gas does 0 work when released to a vacuum, we know that F must = 0.

No it needn't.
The "F" in F=m*a (when talking about rocket propulsion) is the force "forcing"  the mass flow through the nozzle and expelling it from the rocket - with an equal, opposing force accelerating the rocket.
That F is (much) greater than 0. We agree, that m is greater than 0. => The acceleration is greater than 0 and the rocket works in a vacuum.

The F being 0 due to free expansion is a different F and does not apply here (valid reasons haven been provided multiple times and in detail), so the rest of your conclusion is invalid.
You are working with a faulty perception of the process, which unsurprisingly leads you to a wrong conclusion.

iC

[Dr Van Nostrand]

Enough of this highfalutin, book learned, ciphering!

If the explosive reaction of a hand grenade will do work in a vacuum, why won't the explosive reaction of a rocket engine do work?

If I wanted do a bunch of math, I would have been a scientist.

[gurnb]

There are three laws of motion:
1) An object in motion (or at rest) will stay in motion (or at rest) until some outside force acts upon it, or inertia.
2) F= m*a
Since we know that gas does 0 work when released to a vacuum, we know that F must = 0.

Since we know that gas has mass, then m =/= 0.

If m =/= 0, that must mean that a = 0, since the only way to obtain a product of 0 is... either the multiplicand or multiplier must = 0.

Go back to 1st semester physics class idiot.

[J-Man]

Need we say more? he he

[stack]

Need we say more? he he

More about what exactly? How is this proof of a fake moon landing or rockets not working in space?

[BRrollin]

Enough of this highfalutin, book learned, ciphering!

If the explosive reaction of a hand grenade will do work in a vacuum, why won't the explosive reaction of a rocket engine do work?

If I wanted do a bunch of math, I would have been a scientist.

I don’t think they’re gonna bite on this grenade idea, bro. Let’s move on.

Also, the rocket explosion is a deflagration, but the grenade is a detonation. So the energy is transported using different mechanisms. It’s...really not the best analogy to use if ya wanna push the thermo angle.

I think a clearer picture is to focus on momentum strictly. Conversations on here tend to fragment early, and pretty soon everyone’s taking about anomalous dilation equivalence recalcitrant tango foxtrot Charlie niner, or something.

Help us stay on track, Dr Kramer.

[AATW]

Need we say more? he he

Well, you literally haven’t said anything, you’ve just posted a video which is about upcoming planned trips to the moon. So he’s, you need to say more. Saying anything would be nice.
What’s your point, caller?

[Dr Van Nostrand]

I don’t think they’re gonna bite on this grenade idea, bro. Let’s move on.

Yeah.....   I have tried a medieval catapult, astronaut throwing a baseball, the recoil of a shotgun. Apparently, it is only rocket engines for which the physics of momentum begin to breakdown.

[ChrisTP]

Need we say more? he he

It's good to see you've changed your mind and now believe NASA went to the moon and are going to hopefully go back. Well done man, this is great progress for you. I didn't think you had it in you but here we are. It's almost like you're a NASA fanboy now! It's great how enthusiastic you are about NASA.

[iCare]

I think a clearer picture is to focus on momentum strictly. Conversations on here tend to fragment early, and pretty soon everyone’s taking about anomalous dilation equivalence recalcitrant tango foxtrot Charlie niner, or something.

Unfortunately, your a right. When the main argument cannot be easily disputed, people tend to go of into specific examples (under special conditions) or special cases and then try to either deflect from the real question or reverse engineer a (perceived) contradiction (or both). 

I don't know since when you've been reading along, but there were many posts by several people making good and convincing cases for rockets working in any environment by focusing on momentum.
I referenced one example, which will get you to the general location of the discussion in this thread.
(On a side note: The quotes totallackey uses out of context in his signature to create the impression of a contradiction are from that discussion.)

Your "take on things" requires that you explain within those laws of physics ,

And so I have done, several times, at length.
Latest example:

Newton's Laws do not prevent rockets from functioning in a vacuum, they require them to function.
As explained before when one mass is accelerated one way, another mass moves must be accelerated the opposite way.
This is a basic law and it is easily observable that gas (which as a mass) is leaving the rocket; to do that it must accelerate.
If you wan't a rocket to fail in a vacumm you must dispute Newton's laws.

It should be quite obvious, that a rocket works because of Newton's Laws.
Mass (gas) is exhausted (accelerated) one way, consequently a corresponding mass (rocket) needs to accelerate the other way.
Newton's Laws are independent of the environment; nowhere does it say "Newton's Laws only work in an atmosphere.".
=> It really is up to you, to prove (or at least explain), why you dispute Newton's Laws.

As far as I remember, all "prove" was (wrongly) based Joule's Law, which lead to the discussion of thermodynamics.

You are the one claiming that gas can be somehow "FORCED," into a vacuum.
For the final time, it cannot.
Joules proved this.

You can call it final as often as you want, that is not what Joules proved.
If there is no resistance, gas does not need to be forced; it does not mean it cannot be forced.
If you let go of a ball, you don't need to push it to fall down; that doesn't mean you can't still throw it down.
With a rocket engine there is resistance by the simple fact of the nozzle restricting the flow of gas created by the chemical reaction. There is a force. This is not (in conflict) with Joule's law of Free Expansion.

You cannot "FORCE," gas into a vacuum.
Gas, when released to a vacuum, finds no container, and freely expands.
As proven by Joules.

Joules has proven, that gas meeting no resistance in an enlarging volume (as part of it is contains a vacuum) expands freely within the volume.
He has not proven, that

• it cannot be forced.
• this would also be the case, if it were expanding "outside" a closed volume (he didn't have the means to do such an experiment).
• this would also be the case, if energy were added to that gas (that is explicitly prevented in his free expansion experiment).

So, as explained by several people in several ways:

• Newton's Laws require rockets to work in space/a vacuum.
• This is not in conflict with Joule's Law of Free Expansion.
• Rockets work in space/a vacuum.

iC