Re: Rockets work in a vacuum
« Reply #20 on: November 19, 2022, 08:53:41 PM »
It doesn't push against anything.  There's no friction.  Its a reaction.  Read the book. 

"And stack, Newton made it clear that MASS is important in the action/reaction equation.  The greater the mass of one object compared to another, the less it will move".

Correct.  You're probably thinking "Gas?  That's not got a lot of mass".  Try to understand that this was the heaviest rocket that NASA has ever launched, and that around 90% of the Lift-Off Mass of a rocket is fuel and oxidiser.  And all that mass gets thrown out of the nozzle.  It burns, and it becomes gaseous, but when it flies out of the nozzle at supersonic speed it still has the same mass it had when it was a zillion gallons of liquid oxygen and hydrogen

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Offline Tron

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Re: Rockets work in a vacuum
« Reply #21 on: November 20, 2022, 08:38:02 AM »
If Jets and Rockets are propelled as a reaction to moving the mass of fuel at a high velocity in one direction rather than on the exhaust fumes pushing against air, then there should be some information which could confirm the answer. 

Do Rockets and Jet engines maintain constant thrust regardless of their altitude, air pressure, or speed? I understand Jets depend on air intake for power so maybe this can't be answered.  But this kind of data would help understand what principles are propelling these vehicles.
From the surface Earth looks flat.  From space Earth looks round.  Now what?

Offline SteelyBob

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Re: Rockets work in a vacuum
« Reply #22 on: November 20, 2022, 09:14:42 AM »
If Jets and Rockets are propelled as a reaction to moving the mass of fuel at a high velocity in one direction rather than on the exhaust fumes pushing against air, then there should be some information which could confirm the answer. 

Do Rockets and Jet engines maintain constant thrust regardless of their altitude, air pressure, or speed? I understand Jets depend on air intake for power so maybe this can't be answered.  But this kind of data would help understand what principles are propelling these vehicles.

The answer to that is in the equation that I showed you, which is repeated on the diagram that you posted. Look at the terms in the equation - all the answers are there.

Notice that there isn’t a term for the rocket’s velocity - so, no, thrust doesn’t depend on the velocity of the vehicle.

But there is a term involving the static pressure. So yes, thrust does change with altitude. It actually increases as pressure reduces, so, and I’m now repeating myself from an earlier post, when you get to what is essentially a vacuum in space thrust is maximised.

Again, all of this is testable and proven down here on earth. If you’re arguing that rockets wouldn’t work in a vacuum it’s important to understand that you aren’t just arguing about that, you are challenging the entire physics behind how rockets work - principles that have been proven numerous times in both labs and flight tests.

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Offline Tron

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Re: Rockets work in a vacuum
« Reply #23 on: November 20, 2022, 09:25:38 AM »
I'll take a closer look at the Thrust equation...  I appreciate your feedback.
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Re: Rockets work in a vacuum
« Reply #24 on: November 20, 2022, 01:08:21 PM »
If Jets and Rockets are propelled as a reaction to moving the mass of fuel at a high velocity in one direction rather than on the exhaust fumes pushing against air, then there should be some information which could confirm the answer


There is information; its called Newton's Third Law.  Google it.  Its plainly written in practically every book about physics.  You act on an object, and it exerts an identical force on you, but in the opposite direction.  Its skateboard-guy with a bowling ball. 

The exhaust fumes are not pushing on air.  Fuel itself is not moved backwards, it is the exhaust gas which moves; -

Rocket; the fuel/oxidiser in the tanks combine and burn to produce hot gas, which has a hugely greater volume so is directed out of the nozzle and is termed "exhaust".  The volume is increased, but the mass remains the same.  The mass is therefore accelerated, which is a force.  The force of accelerating the exhaust produces a reaction on the rocket, in the opposite direction. Whatever is outside the nozzle (air, vacuum, yogurt) doesn't matter.

Jet; The aircraft only carries fuel, not oxidiser.  It collects air through an intake.  The air serves 2 functions;
1. it contains oxygen, so supports combustion. 
2. It has mass. 
Fuel is combined with the air and burnt, which increases the volume and pressure of the gas.  The fuel doesn't contribute much to the mass, the exhaust gas is mainly air and combustion products like CO, CO2, water, but whilst the volume is much greater it still has the same mass.  The gas escapes through the jetpipe, and is termed "exhaust".  The mass is therefore accelerated, which is a force.  The force of accelerating the exhaust produces a reaction on the aircraft, in the opposite direction. Whatever is outside the nozzle (air, vacuum, yogurt) doesn't matter, but unfortunately the intake needs to be immersed in air, so the rest of the aircraft has the same limitation. 

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Offline Tron

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Re: Rockets work in a vacuum
« Reply #25 on: November 20, 2022, 01:21:10 PM »
This opposite force created by accelerating matter is new to me...  I'll investigate and thank you for your time.
From the surface Earth looks flat.  From space Earth looks round.  Now what?

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Offline Tumeni

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Re: Rockets work in a vacuum
« Reply #26 on: November 20, 2022, 02:45:46 PM »
If Jets and Rockets are propelled as a reaction to moving the mass of fuel at a high velocity in one direction rather than on the exhaust fumes pushing against air, then there should be some information which could confirm the answer.

.... which will be found in one or more textbooks on the subject written in the last 70 years or so.

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Re: Rockets work in a vacuum
« Reply #27 on: November 20, 2022, 03:56:45 PM »
This opposite force created by accelerating matter is new to me...  I'll investigate and thank you for your time.

We had talked about this at the beginning of the thread.

If the proposition is that rockets push off air to move, this can be disproven at home. Reaction force can be found to not rely on atmosphere.

Solving for air resistance involves knowing the cross sectional area exposed to air. Remember that.

If I throw a 10-pound metal ball of some diameter while standing on a skateboard, I will move X distance.

If I throw a 10-pound metal ball of a SMALLER diameter while standing on a skateboard, I will move the exact same distance.

The mass stayed the same, the distance stayed the same, and yet the cross sectional area changed. This experimentally shows that air resistance does not affect reaction force.

Now replace the skateboard with a rocket, metal balls with gas being accelerated EXTREMELY fast, and me “throwing” with a very violent chemical reaction.



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Offline Tron

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Re: Rockets work in a vacuum
« Reply #28 on: November 20, 2022, 04:27:08 PM »
I'm afraid to continue this argument because I don't want to come accross as disrespectful...  I get your point.  It's sinking in.   I'd be lying if I said I can conceptualize this fully though.

Questions like.. if exhaust fumes do nothing compared to the internal action/reaction principle, then what happens if we move the exhaust of a jet in different directions?  Nothing really?  What if we turned the exhaust of  a rocket 180 degrees...  Would the rocket still move forward?  I'm compelled to give credit to the enormous wind power generated by these machines.

But seriously, I know I am a newbie to mechanics so I will read and probably start experimenting with household objects like a garden hose and how much recoil I get at different water settings.. 

From the surface Earth looks flat.  From space Earth looks round.  Now what?

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Offline markjo

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Re: Rockets work in a vacuum
« Reply #29 on: November 20, 2022, 04:32:13 PM »
This opposite force created by accelerating matter is new to me...  I'll investigate and thank you for your time.
It's simply an example of Newton's third law of motion.

If you want the simple explanation of how rockets work in a vacuum, then it's action/reaction.  If you want a detailed explanation...  Well, there's a reason that the term "rocket science" is used to describe something difficult.
« Last Edit: November 20, 2022, 04:34:13 PM by markjo »
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Re: Rockets work in a vacuum
« Reply #30 on: November 20, 2022, 05:31:42 PM »

Questions like.. if exhaust fumes do nothing compared to the internal action/reaction principle, then what happens if we move the exhaust of a jet in different directions?  Nothing really?  What if we turned the exhaust of  a rocket 180 degrees...  Would the rocket still move forward?  I'm compelled to give credit to the enormous wind power generated by these machines.

Harrier; it can deflect its exhaust nozzle downwards; plane goes up.
Airliners; ducts and vanes deflect the exhaust gas forwards; plane slows down. 

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Offline stack

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Re: Rockets work in a vacuum
« Reply #31 on: November 20, 2022, 06:30:23 PM »
This opposite force created by accelerating matter is new to me...  I'll investigate and thank you for your time.

Tron, just examine this:



What's really interesting about it is that the sled on the left is propelled at half the speed at the the sled on the right. Reason being, the left sled is twice the mass as the right sled sled. Pretty cool how that works.

Additionally, it's a pretty clear example of Newton's 3rd. You have to ask yourself why do the sleds both propel and why do they propel opposite one another. It clearly demonstrates exactly what you mentioned: "opposite force created by accelerating matter".

Keep exploring. There's lots of cool stuff around rockets, physics, etc.

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Offline Tom Bishop

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Re: Rockets work in a vacuum
« Reply #32 on: November 20, 2022, 06:56:44 PM »
This opposite force created by accelerating matter is new to me...  I'll investigate and thank you for your time.

Tron, just examine this:



What's really interesting about it is that the sled on the left is propelled at half the speed at the the sled on the right. Reason being, the left sled is twice the mass as the right sled sled. Pretty cool how that works.

Additionally, it's a pretty clear example of Newton's 3rd. You have to ask yourself why do the sleds both propel and why do they propel opposite one another. It clearly demonstrates exactly what you mentioned: "opposite force created by accelerating matter".

Keep exploring. There's lots of cool stuff around rockets, physics, etc.

Since it appears that you have discovered Newton's laws, and know that different amount of mass will be moved differently in response to a force, more massive requiring more force, maybe you can explain for us how gravity knows to apply different amounts of force to a bowling ball and a feather to cause them to 'fall' together at the same rate in a vacuum chamber.

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Offline markjo

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Re: Rockets work in a vacuum
« Reply #33 on: November 20, 2022, 07:03:43 PM »
Since it appears that you have discovered Newton's laws, and know that different amount of mass will be moved differently in response to a force, more massive requiring more force, maybe you can explain for us how gravity knows to apply different amounts of force to a bowling ball and a feather to cause them to 'fall' together at the same rate in a vacuum chamber.
If you want to discuss gravity, then feel free to start a new thread.  This thread is about how rockets work in a vacuum.
Abandon hope all ye who press enter here.

Science is what happens when preconception meets verification.

Ignorance more frequently begets confidence than does knowledge. -- Charles Darwin

If you can't demonstrate it, then you shouldn't believe it.

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Offline Tom Bishop

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Re: Rockets work in a vacuum
« Reply #34 on: November 20, 2022, 07:06:36 PM »
Since it appears that you have discovered Newton's laws, and know that different amount of mass will be moved differently in response to a force, more massive requiring more force, maybe you can explain for us how gravity knows to apply different amounts of force to a bowling ball and a feather to cause them to 'fall' together at the same rate in a vacuum chamber.
If you want to discuss gravity, then feel free to start a new thread.  This thread is about how rockets work in a vacuum.

If you want to appeal to Newton then you have to be willing to talk about places where Newton's laws don't work. How rockets work, and rocketry requirements, does have something to do with gravity. A lot to do with it, actually. Simply: Gravity in not coherent with the laws of Newton, yet you want to use Newton's inconsistent laws to prove something about the functionality of rockets and how they propel.
« Last Edit: November 20, 2022, 07:09:06 PM by Tom Bishop »

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Offline markjo

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Re: Rockets work in a vacuum
« Reply #35 on: November 20, 2022, 07:07:57 PM »
Since it appears that you have discovered Newton's laws, and know that different amount of mass will be moved differently in response to a force, more massive requiring more force, maybe you can explain for us how gravity knows to apply different amounts of force to a bowling ball and a feather to cause them to 'fall' together at the same rate in a vacuum chamber.
If you want to discuss gravity, then feel free to start a new thread.  This thread is about how rockets work in a vacuum.

If you want to appeal to Newton then you have to be willing to talk about places where Newton's laws don't work. How rockets work, and rocketry requirements, does have something to do with gravity. A lot to do with it, actually.
Gravity is not one of Newton's three laws of motion.
Abandon hope all ye who press enter here.

Science is what happens when preconception meets verification.

Ignorance more frequently begets confidence than does knowledge. -- Charles Darwin

If you can't demonstrate it, then you shouldn't believe it.

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Offline SteelyBob

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Re: Rockets work in a vacuum
« Reply #36 on: November 20, 2022, 07:08:26 PM »
This opposite force created by accelerating matter is new to me...  I'll investigate and thank you for your time.

Tron, just examine this:



What's really interesting about it is that the sled on the left is propelled at half the speed at the the sled on the right. Reason being, the left sled is twice the mass as the right sled sled. Pretty cool how that works.

Additionally, it's a pretty clear example of Newton's 3rd. You have to ask yourself why do the sleds both propel and why do they propel opposite one another. It clearly demonstrates exactly what you mentioned: "opposite force created by accelerating matter".

Keep exploring. There's lots of cool stuff around rockets, physics, etc.

Since it appears that you have discovered Newton's laws, and know that different amount of mass will be moved differently in response to a force, more massive requiring more force, maybe you can explain for us how gravity knows to apply different amounts of force to a bowling ball and a feather to cause them to 'fall' together at the same rate in a vacuum chamber.

I agree - this is different thread territory.

Since you asked, however…because the gravitational force between two objects depends on the mass of both objects. If that seems implausible, it is no different to, for example, the force between two charged particles, where the mutual force depends on the charge of both particles.

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Offline Tom Bishop

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Re: Rockets work in a vacuum
« Reply #37 on: November 20, 2022, 07:14:51 PM »
Since you asked, however…because the gravitational force between two objects depends on the mass of both objects. If that seems implausible, it is no different to, for example, the force between two charged particles, where the mutual force depends on the charge of both particles.

Actually it's much different.

Particles charged with different amounts of force and charge will produce different levels of attraction.

Different masses of particles will also accelerate at different accelerations due to their inertial drag, for the same reason why it is harder to push a bowling ball across the floor than a marble. More mass means more inertial resistance.

Gravity behaves differently than this, however. All bodies fall together at the same rate in a laboratory vacuum chamber regardless of their mass. No difference has been detected. This even applies to individual atoms with different masses.
« Last Edit: November 20, 2022, 07:16:24 PM by Tom Bishop »

Re: Rockets work in a vacuum
« Reply #38 on: November 20, 2022, 07:30:26 PM »
Gravity behaves differently than this, however. All bodies fall together at the same rate in a laboratory vacuum chamber regardless of their mass. No difference has been detected. This even applies to individual atoms with different masses.

Why did you come into a thread about rockets in a vacuum and start asking us questions about gravity that you can readily find the answers to elsewhere?

Do you agree or disagree that rockets work in a vacuum?

Offline SteelyBob

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Re: Rockets work in a vacuum
« Reply #39 on: November 20, 2022, 07:48:47 PM »
Since you asked, however…because the gravitational force between two objects depends on the mass of both objects. If that seems implausible, it is no different to, for example, the force between two charged particles, where the mutual force depends on the charge of both particles.

Actually it's much different.

Particles charged with different amounts of force and charge will produce different levels of attraction.

You are mixing terms here. You don't charge a particle with 'force and charge'.

Two particles will experience a mutual attractive or repelling force depending on the product of the two charges and the inverse of the square of the distance between them. This is Coulomb's law. The formula is essentially the same as the formula for the gravitational force between two objects, it's just that the two charges are replaced by the two masses, and the constant is of course different.

If you take issue with one formula, then you must take issue with both. Your original question appears to misunderstand or misrepresent the problem, implying the force is only on one object. You are missing out that when gravity acts on, for example, a feather, there is actually a mutual force acting between the feather and the earth. We obviously tend to neglect the force on the earth as it is so trivial, but the principle is no different to that of two charged particles, one with a massive charge and the other with a negligible one.

Different masses of particles will also accelerate at different accelerations due to their inertial drag, for the same reason why it is harder to push a bowling ball across the floor than a marble. More mass means more inertial resistance.

Gravity behaves differently than this, however. All bodies fall together at the same rate in a laboratory vacuum chamber regardless of their mass. No difference has been detected. This even applies to individual atoms with different masses.

An object will accelerate in direct proportion to the net force acting upon it. An object experiencing a gravity force from a planet, such as earth, will experience a force in proportion to its own mass. Double the mass, and double the force. That is why objects of different mass accelerate at the same rate when falling under gravity. Clearly, in the real world, air resistance steps in and causes differences, but as you rightly say, in vacuum conditions no difference is detected. That is precisely what we would expect from the principles.