Talk:Thrust

'Pounds of thrust'

Americans use the strange construction 'pounds of thrust', but thrust means 'force', which in the rational SI system is measured in Newtons not kilograms. Force = mass x acceleration so what is the implied a? Earth gravity? How is that useful outside rocketry? Putting the philology question aside, would someone who understands US customary units please add a section that explains US usage? — Preceding unsigned comment added by 88.97.11.54 (talk) 17:17, 12 June 2016 (UTC)

Now resolved. See pound of thrust which redirects to pound (force). --John Maynard Friedman (talk) 13:01, 1 August 2019 (UTC)

What about thrust in vacuum

This isn't the place to promote fringe theories.

This article seems less than scientific. Thrust should be designated as a form of "energy". The question that should be explicitly answered is the energy "momentum" or can it be properly measured as kinetic energy. In vacuum of space navigation using the kinetic energy formulation "1/2vmv" will not accurately predict the outcome a given thrust will produce. Nor will it accurately predict what force is required to produce that thrust. Thrust proves momentum is the only form of real energy. If the article is to be defended you should have the credible testimony of a physicist stating that thrust applied in outer space has performance that is consistent with the kinetic energy theorem. You should also note that the article makes no mention of the thrusters used to navigate in vacuum. Simple question the article should be able to answer: If I throw 1 unit of mass moving 1,000 miles per hour out one side of my spaceship, and simultaneously 1,000 units of mass going 1 mph out the other side. Does the spaceship turn? If it doesn't how can kinetic energy be considered "real energy" when I have thrown a thousand times "more energy" one way than the other? Draft Physics (talk) 18:36, 14 February 2024 (UTC) Neither thrust (a force) nor momentum is energy. Different units of measurement. In your thought experiment it takes much more energy to get the 1 unit of mass moving at 1,000 units of velocity than it takes to get 1,000 units of mass moving one unit of velocity. The article does discuss rocketry, briefly, noting its similarity to jet propulsion. There probably is room for more discussion of the rocket thrust equation, etc, but we would need to cite reliable sources, not thought experiments. VQuakr (talk) 19:15, 14 February 2024 (UTC) "Neither thrust (a force) nor momentum is energy" what's your Authority for that opinion? Quoting Newton "twice the force equals twice the movement" you're claiming that movement isn't energy? "it takes much more energy to get the 1 unit of mass moving at 1,000 units of velocity than it takes to get 1,000 units of mass moving one unit of velocity." what's your Authority for that statement. And how is it consistent with Newton's third law? The same explosion makes the bullet have more "energy" than the gun recoil? "The article does discuss rocketry, briefly, noting its similarity to jet propulsion." only in the context of atmospheric or gravitational drag. "There probably is room for more discussion of the rocket thrust equation." The rocket equation is only relevant in circumstances where fuel has substantial Mass... It would have little use if you were using a nuclear fuel. "we would need to cite reliable sources, not thought experiments." Isaac Newton should be considered a reliable source, in his second law he explicitly stated "twice the force twice the movement." In my opinion good science requires thought experiments. As stated the page should be able to answer the question...If I throw 1 unit of mass moving 1,000 miles per hour out one side of my spaceship, and simultaneously 1,000 units of mass going 1 mph out the other side. Does the spaceship turn? Can you answer the question? More precisely will you answer the question and demonstrate you know what you're talking about. Draft Physics (talk) 03:40, 15 February 2024 (UTC) If you have questions about basic physics like force vs momentum vs kinetic energy, you can ask them at the reference desk. The presence of drag is what differentiates thrust in space from thrust in an atmosphere or other medium. No I was talking about the thrust equation, ${\begin{aligned}F&={\dot {m}}v_{\text{e}}+\left(p_{\text{e}}-p_{\text{o}}\right)A_{\text{e}}\\[2pt]&={\dot {m}}\left[v_{\text{e}}+\left({\frac {p_{\text{e}}-p_{\text{o}}}{\dot {m}}}\right)A_{\text{e}}\right],\end{aligned}}$ not the rocket equation. See Rocket engine nozzle. Nuclear engines still have significant mass flow rate though; they're just more efficient than chemical rockets. See WP:RELIABLE regarding sources and "thought experiments". Newton is a reliable source for what Newton said, not on modern day physics. VQuakr (talk) 06:34, 15 February 2024 (UTC) Thanks for the reply. The accusation is that thrust is entirely controlled by momentum, and that for example, the kinetic energy theorem would crash you on the moon rather than land you on the moon. If you have questions about basic physics like force vs momentum vs kinetic energy, you can ask them at the reference desk. I'm making the direct accusation that your Wikipedia page is not good science. It is superficial, vague and slanders Isaac Newton. Show me the experiment where it takes 25 the energy to spin an object five times as fast. Newton is a reliable source for what Newton said, not on modern day physics. The first sentence of the wiki page sites Newton's third law. The third law was written describing momentum not kinetic energy. Newton was not a leibnizian. Modern physics says a bullet has 2,000j while the gun recoil is only 2j, how is that consistent with the third law? If I shot the bullet out one side of my ship and allowed a gun recoil to shoot out the other would the ship turn? This is the third time I've asked the question? The Wiki page should provide the answer to the question. The fact is little things going fast is not more "thrust" than big things going slow and the Wiki page should be clear on that. Draft Physics (talk) 15:26, 15 February 2024 (UTC) "The accusation is that thrust is entirely controlled by momentum, and that for example, the kinetic energy theorem would crash you on the moon rather than land you on the moon." You've yet to substantiate this, which would involve overturning mathematics itself. "I'm making the direct accusation that your Wikipedia page is not good science." You've yet to substantiate this. Moving on. "It is superficial, vague and slanders Isaac Newton." Everything you've written so far is loaded with severe misunderstanding of basic physics concepts. What piece of text "slanders Newton?" "Show me the experiment where it takes 25 the energy to spin an object five times as fast." Look into wind turbine power generation curves. This stuff is not new. "The first sentence of the wiki page sites Newton's third law. The third law was written describing momentum not kinetic energy. Newton was not a leibnizian." This is a non-sequitur. "Modern physics says a bullet has 2,000j while the gun recoil is only 2j, how is that consistent with the third law?" Because the corollary of Newton's third law pertains to momentum, not kinetic energy, as you said yourself. Therefore, the fact that a bullet has "2,000j" while the gun has "2j" is not a contradiction to Newton's third law, because Joules is a measure of energy, not momentum. "If I shot the bullet out one side of my ship and allowed a gun recoil to shoot out the other would the ship turn?" I am answering for the second time: no and this does not violate any known physics. Selbram (talk) 15:43, 15 February 2024 (UTC) Modern physics says a bullet has 2,000j while the gun recoil is only 2j, how is that consistent with the third law? Because Newton's third law talks about momentum (units kg*m/s) instead of energy (units Joules). How is this so difficult for you to understand? Selbram (talk) 15:57, 15 February 2024 (UTC) You should be aware that Draft Physics is a known dishonest actor online who has been slandering anyone he interacts with. He has lied about the fact that no one answers his questions or that no one provides him with evidence. He tries to advocate for the false idea that Newton thought that F = mv, that somehow everyone does not realize this, yet at the same time people use this fact nonetheless. The kind of stuff Draft Physics brings up is unimaginably nonsensical. Please be very careful with this person. Selbram (talk) 15:47, 15 February 2024 (UTC) Let's go over a couple of facts that seem to go over your head or you seem to deny, shall we? After all, you are very interested in facts, right? First off, force, momentum, and energy are distinct concepts according to every existing physics and engineering source, including all existing textbooks that all NASA engineers and scientists learn from. This has been understood about Newtonian mechanics since the 1800's. Your made-up imagination of what you think Newtonian mechanics is does not substitute actual physics practiced by every working mechanical engineer around the world. When you said, "Quoting Newton "twice the force equals twice the movement" you're claiming that movement isn't energy," you took the quote out-of-context. The original statement of Newton reads, "The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed. If a force generates a motion, a double force will generate double the motion, a triple force triple the motion, whether that force be impressed altogether and at once, or gradually and successively. And this motion (being always directed the same way with the generating force), if the body moved before, is added to or subtracted from the former motion, according as they directly conspire with or are directly contrary to each other; or obliquely joined, when they are oblique, so as to produce a new motion compounded from the determination of both." where "quantity of motion" stood for mass times velocity. The alteration of motion is the rate of change in motion, meaning $d(mv)/dt$, which is proportional to force. Thus, $F ∝ d(mv)/dt$. For a constant mass, this yields $F ∝ ma$. This directly contradicts your claim that $F = mv$ which is exactly what Newton argued against. This was the entire revelation of Newtonian mechanics that set it apart from previous attempts at understanding physics: Force is not linearly proportional to velocity unlike what previous thinkers thought. See https://www.physics.utoronto.ca/~jharlow/teaching/everyday06/reading01.htm So no, force is neither energy nor momentum. You are just confused, akin to a flat Earther. ""it takes much more energy to get the 1 unit of mass moving at 1,000 units of velocity than it takes to get 1,000 units of mass moving one unit of velocity." what's your Authority for that statement." The authority are the experiments that have been shown to you on your channel countless of times. "And how is it consistent with Newton's third law?" Newton's third law implies when two stationary items are pushed apart, they will have equal and opposite momenta. This law says nothing as to what proportion of energy the two items will have. So this is all consistent with Newton's third law. You didn't find any contradiction, and your inability to grasp this does not count as a contradiction. ""The article does discuss rocketry, briefly, noting its similarity to jet propulsion." only in the context of atmospheric or gravitational drag." What equations don't apply outside the context of atmospheric or "gravitational" drag? ""we would need to cite reliable sources, not thought experiments." Isaac Newton should be considered a reliable source, in his second law he explicitly stated "twice the force twice the movement."" And yet again, you do quote-mining. Twice the force overall means the final speed is twice, but the main context of Newton's second law is not in that quote fragment, but in the actual main statement of the law, which you seem to be conveniently leaving out. I'm not going to repeat myself in this post, but it will be clear that this will have to be repeated to you. "In my opinion good science requires thought experiments. As stated the page should be able to answer the question...If I throw 1 unit of mass moving 1,000 miles per hour out one side of my spaceship, and simultaneously 1,000 units of mass going 1 mph out the other side. Does the spaceship turn? Can you answer the question?" No the spaceship does not turn. This question is trivially answerable and it does not overturn any piece of physics that you think it will. Selbram (talk) 10:57, 15 February 2024 (UTC) Let's go over a couple of facts that seem to go over your head or you seem to deny, shall we? I've spent 10 years researching the facts and I have a standing offer of $2,000 for proof that any of my assertions are incorrect. After all, you are very interested in facts, right? You're interest seems to be arrogant snarkiness First off, force, momentum, and energy are distinct concepts according to every existing physics and engineering source , including all existing textbooks Too bad the sources don't cite evidence... Show me the evidence it takes 100 times of fuel to spin a motor 10 times as fast. that all NASA engineers and scientists learn from. NASA is rather famous for saying it only used Newtonian mechanics to land on the Moon. Show me a NASA scientist proving it takes 25 times the fuel to go five times as fast. This has been understood about Newtonian mechanics since the 1800's. What experiment was performed in the 1800s that shows Newton and Galileo wrong? Your made-up imagination of what you think Newtonian mechanics is does The experiment where it takes 25 times to fuel to go five times as fast clearly only exist in your imagination. not substitute actual physics practiced by every working mechanical engineer around the world. Show me the water wheel requiring four times the water pressure to spin twice as fast. When you said, "Quoting Newton "twice the force equals twice the movement" you're claiming that movement isn't energy," you took the quote out-of-context. This was the first sentence of newton's defense of his second law. I took nothing out of context. Newton believed in momentum he opposed the leibnizian theory of kinetic energy (vmv). The original statement of Newton reads, "The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed. If a force generates a motion, a double force will generate double the motion, a triple force triple the motion, whether that force be impressed altogether and at once, or gradually and successively. And this motion (being always directed the same way with the generating force), if the body moved before, is added to or subtracted from the former motion, according as they directly conspire with or are directly contrary to each other; or obliquely joined, when they are oblique, so as to produce a new motion compounded from the determination of both." where "quantity of motion" stood for mass times velocity. So where is the inconsistency with anything I asserted? The alteration of motion is the rate of change in motion, meaning $d(mv)/dt$, which is proportional to force. Thus, $F ∝ d(mv)/dt$. Where did Newton say any of that? Newton said 9.8 m per one second, not any number of seconds, and certainly not per second squared. You are the one misrepresenting what Newton said. For a constant mass, this yields $F ∝ ma$. This directly contradicts your claim that $F = mv$ which is exactly what Newton argued against. This was the entire revelation of Newtonian mechanics that set it apart from previous attempts at understanding physics: Force is not linearly proportional to velocity unlike what previous thinkers thought. This is a slanderous misinterpretation of Newton... Newton clearly said force is proportionally equal to momentum. And he directly opposed the leibnizing theory claiming a lack of proportionality. So no, force is neither energy nor momentum. You are just confused, akin to a flat Earther. Flat earthers are not confused they are liars. A proportional equality to people who resort to name calling when they can't make an argument. ""it takes much more energy to get the 1 unit of mass moving at 1,000 units of velocity than it takes to get 1,000 units of mass moving one unit of velocity." what's your Authority for that statement." The authority are the experiments that have been shown to you on your channel countless of times. Just link me to an experiment showing it taking 25 times to fuel to spin something five times as fast "And how is it consistent with Newton's third law?" Newton's third law implies when two stationary items are pushed apart, they will have equal and opposite momenta. This law says nothing as to what proportion of energy the two items will have. Obviously Newton considered momentum energy (quantity of motion). So this is all consistent with Newton's third law. So different energies going in different directions is consistent with Newton's third law? You didn't find any contradiction, and your inability to grasp this does not count as a contradiction. Well there's no contradiction if you believe vocabulary should be meaningless. "The article does discuss rocketry, briefly, noting its similarity to jet propulsion." only in the context of atmospheric or gravitational drag." What equations don't apply outside the context of atmospheric or "gravitational" drag? "we would need to cite reliable sources, not thought experiments." Isaac Newton should be considered a reliable source, in his second law he explicitly stated "twice the force twice the movement." And yet again, you do quote-mining. You are clearly the one putting words in Newton's mouth he never wrote or spoke. Twice the force overall means the final speed is twice, but the main context of Newton's second law is not in that quote fragment, but in the actual main statement of the law, which you seem to be conveniently leaving out. Newton statement is direct and clear. I'm not going to repeat myself in this post, but it will be clear that this will have to be repeated to you. Repeating a made-up fact is not a reasonable argument "In my opinion good science requires thought experiments. As stated the page should be able to answer the question...If I throw 1 unit of mass moving 1,000 miles per hour out one side of my spaceship, and simultaneously 1,000 units of mass going 1 mph out the other side. Does the spaceship turn? Can you answer the question?" No the spaceship does not turn. If kinetic energy cannot move matter in empty space than it is silly to call it energy. This question is trivially answerable and it does not overturn any piece of physics that you think it will. It is decisive evidence against the kinetic energy Theory/leibnizian mechanics Draft Physics (talk) 16:37, 15 February 2024 (UTC) This is boring. 69.247.66.204 (talk) 08:15, 15 February 2024 (UTC)