The Naked Scientists

The Naked Scientists Forum

Author Topic: thrust does not work in space  (Read 8770 times)

alancalverd

  • Hero Member
  • *****
  • Posts: 1349
    • View Profile
Re: thrust does not work in space
« Reply #125 on: 25/08/2014 13:32:03 »
Again it is really great that you take the time to try to explain this, Thank you, all.

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

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

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

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

Reality207

  • Newbie
  • *
  • Posts: 22
    • View Profile
Re: thrust does not work in space
« Reply #126 on: 25/08/2014 15:58:38 »
Alan wrote, "then give an impulse to m so that it attains a velocity v,"
I understand all that and I agree except for that one little part, I seem to be hung up on again or still,  how is the impulse provided, where does V come from??

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


Do submarines interest you?

Reality207

  • Newbie
  • *
  • Posts: 22
    • View Profile
Re: thrust does not work in space
« Reply #127 on: 25/08/2014 16:12:20 »
I have a propulsion system that will put submarines over a hundred miles an hour.  EASILY
G-Force that will cause one to pass out, move through water like it was air.
On everything that I am, everything that I have,  I guarentee it!

Something like that worth anything $$, to whom? and how would one, "cash it in"?



jeffreyH

  • Hero Member
  • *****
  • Posts: 984
    • View Profile
Re: thrust does not work in space
« Reply #128 on: 25/08/2014 18:35:35 »
Jeff wrote,
"If you were to throw 1000 rocks simultaneously at object it will move. The rocks have left the hands before they start to move the object so where is the push backwards? It is the recoil of the rocks from the surobjeface of the object being moved as per Newton."

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

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

The hand most definitely does not represent the rocket. The hand represents the centre of the explosive release of the gases. The rocket is to be considered a separate system entirely from the ignited gases otherwise you are bootstrapping a system under its own power which is nonsense. The expanding gases push EVERYTHING away from them including the rocket. That is why there is an outlet for the gases AT THE BACK.

alancalverd

  • Hero Member
  • *****
  • Posts: 1349
    • View Profile
Re: thrust does not work in space
« Reply #129 on: 25/08/2014 19:03:07 »
Alan wrote, "then give an impulse to m so that it attains a velocity v,"
I understand all that and I agree except for that one little part, I seem to be hung up on again or still,  how is the impulse provided, where does V come from??

The impulse comes from burning fuel. This converts the potential energy of the mass m of fuel into kinetic energy = mv2/2, hence we have m and v, thus the rocket moves at v' so that Mv' balances mv.

Quote
Before momentium is conserved, it must be stablished or its just potential, right?
Sorry, this is meaningless. Momentum is always conserved. You must appreciate the difference between ∂93f79fa4fc25dddadccc26d0110393b2.gifmv = 0 (the sum of momentum vectors doesn't change) and ∂93f79fa4fc25dddadccc26d0110393b2.gifmv2/2 > 0  (kinetic energy is created from potential energy). Note that v is a vector but v2 is a scalar, which is what it's all about!


Quote
Do submarines interest you?
only as targets.

alancalverd

  • Hero Member
  • *****
  • Posts: 1349
    • View Profile
Re: thrust does not work in space
« Reply #130 on: 25/08/2014 19:05:00 »
I have a propulsion system that will put submarines over a hundred miles an hour.  EASILY
G-Force that will cause one to pass out, move through water like it was air.
On everything that I am, everything that I have,  I guarentee it!

Something like that worth anything $$, to whom? and how would one, "cash it in"?




I think you would need to improve your grasp of elementary physics before presenting it to a potential customer.

dlorde

  • Hero Member
  • *****
  • Posts: 1012
  • ex human-biologist & software developer
    • View Profile
Re: thrust does not work in space
« Reply #131 on: 25/08/2014 23:19:18 »
An ice rink is a good place to get an understanding of these concepts because of the low friction. If you are standing still holding another person and you push them away, they will move away in one direction and you will move in the opposite direction. If you're holding a shopping trolley full of rocks and start throwing them away, one by one, in the same direction, you will get a small impetus in the opposite direction for each rock you throw. The more rocks you throw, the faster you will go. The rocks don't have to hit anything. If you use a fire extinguisher, the gas coming out has the same effect as throwing thousands of tiny rocks - you'll also get an impetus in the opposite direction. In a vacuum it will be even more noticeable because of the lack of air resistance to your motion. That's how a rocket works too. Newton's Third Law.

PmbPhy

  • Sr. Member
  • ****
  • Posts: 309
    • View Profile
Re: thrust does not work in space
« Reply #132 on: 26/08/2014 00:39:47 »
Quote from: Reality207
Jeff wrote,
"If you were to throw 1000 rocks simultaneously at object it will move. The rocks have left the hands before they start to move the object so where is the push backwards? It is the recoil of the rocks from the surobjeface of the object being moved as per Newton."

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

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

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

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

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

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

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

Reality207

  • Newbie
  • *
  • Posts: 22
    • View Profile
Re: thrust does not work in space
« Reply #133 on: 26/08/2014 01:56:07 »
first Thank you for your kind responce.
Now your analogy is completely bogus, as there is something foolish people like me call ATMOSPHERE to resist the ball and allow it to accelerate the person on the skateboard that DOES NOT EXIST IN SPACE.

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

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

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

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

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

PmbPhy

  • Sr. Member
  • ****
  • Posts: 309
    • View Profile
Re: thrust does not work in space
« Reply #134 on: 26/08/2014 02:43:53 »
Quote from: Reality207
first Thank you for your kind responce.
Now your analogy is completely bogus,
That's a rude way to express your thought.

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

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

So! Once again I see that you failed to answer my questions and then expected me to answer yours. That's never going to happen. If you can't be respectful enough to answer a question given to you and you rudely ignore it then there's no way in hell that I'll address yours.
« Last Edit: 26/08/2014 02:55:25 by PmbPhy »

Reality207

  • Newbie
  • *
  • Posts: 22
    • View Profile
Re: thrust does not work in space
« Reply #135 on: 26/08/2014 03:18:37 »
I am preparing my answers, I have been since that last post, not ignoring anyone
I will post it when I complete it and I am doing so.
in fact I was about to post when I read your second past and changed my reply.

Reality207

  • Newbie
  • *
  • Posts: 22
    • View Profile
Re: thrust does not work in space
« Reply #136 on: 26/08/2014 03:37:22 »
Sorry guys if I let my emotions effect me there, pmbphy is not patient like you other
Gentleman, I noticed that in some of his other response.  And I hope I didnít say anything to offend you guys, as you really have been very kind and patient trying to explain this to me.  But the analogies on earth with atmosphere just donít help me understand, as there is no atmosphere in space.  You sit on a chair; the chair pushes back.  Take away the chair; and there is no push back.  Everyone keeps saying Newtonís law I totally agree but how does it apply if there is nothing to push back?  I guess I can understand why I probably up set pmbphy, but that is not my intention. Iím NOT a conspiracy theorist and Iím not trying to prove anything, sorry if I seem that way.

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

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


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

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

Perhaps I should say,
Your student in science LOL

PmbPhy

  • Sr. Member
  • ****
  • Posts: 309
    • View Profile
Re: thrust does not work in space
« Reply #137 on: 26/08/2014 20:51:47 »
Reality207 - Let's start from scratch such as the treatment in Classical Mechanics by John R. Taylor which you can download at http://bookzz.org/book/911552/5131aa

Turn to page 85. That's the page where the section entitle 3.2 Rockets starts. It goes from page 85 to page 87. Please study that section and get back to us.
« Last Edit: 26/08/2014 21:03:56 by PmbPhy »

Reality207

  • Newbie
  • *
  • Posts: 22
    • View Profile
Re: thrust does not work in space
« Reply #138 on: 26/08/2014 21:48:38 »
pmbPhy I will do that.
I am happy to do that.
and Thank You!
ps I was going to me this my last post, I will get back to you.
Your friend,

PmbPhy

  • Sr. Member
  • ****
  • Posts: 309
    • View Profile
Re: thrust does not work in space
« Reply #139 on: 26/08/2014 21:58:07 »
Quote from: Reality207
Sorry guys if I let my emotions effect me there, pmbphy is not patient like you other Gentleman, I noticed that in some of his other response.
Hi Reality207,
I was upset when I saw you write this. You hardly know me so you have no cause to make such a claim such as this. You might have said something like Pmbphy was being impatient since that shows a particular state of mind whereas pmbphy is not patient says something about a personís character which takes a while to learn because you have to get to know them.
Quote from: Reality207
Everyone keeps saying Newtonís law I totally agree but how does it apply if there is nothing to push back?
That is quite correct. Itís what led Einstein to general relativity.
Quote from: Reality207
Einstein to his the- I guess I can understand why I probably up set pmbphy, but that is not my intention.
No problem. Iím finally getting to understand you better now. You could be a great deal more intelligent than I thought you were not that Iíve gone back to studying your posts. :)

Quote from: Reality207
Pmbphy I am a master electrician not a physicist, thatís clear.
This is something we have in common. I started off as an electronics technician and saw that I was capable of doing a hell of a great real more. So I stopped being an electronics technician and went to college, learned math and even though I totally sucked at arithmetic I was wonderful at trigonometry, algebra, geometry, calculus, etc. Itís a good thing I wasnít married since that would have been a problem.
Quote from: Reality207
I am also going to try to understand what Pmbphy wrote between the insults.
Thank you. I'll try to do the same with you too. Think what happened was that you and a lot of people do, i.e. they confuse negative criticism with insults. Have you ever noticed that yourself?
« Last Edit: 26/08/2014 22:06:42 by PmbPhy »

PmbPhy

  • Sr. Member
  • ****
  • Posts: 309
    • View Profile
Re: thrust does not work in space
« Reply #140 on: 26/08/2014 22:00:28 »
pmbPhy I will do that.
I am happy to do that.
and Thank You!
ps I was going to me this my last post, I will get back to you.
Your friend,
That's Wonderful my new friend. I see that we're good to go on this then. Great!  ;D

Reality207

  • Newbie
  • *
  • Posts: 22
    • View Profile
Re: thrust does not work in space
« Reply #141 on: 27/08/2014 02:30:57 »
Hi guys,
Maybe there is no hope for me :-'(

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

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


John Taylor wrote - ďwhen you push one way on the boot, the boot pushes in the opposite direction on you.Ē  I donít understand that, sorry (and I almost want to tremble to say this) I donít see just the boot pushing as JT states.  The boot and the arm in motion push against the atmosphere and the atmosphere pushes back against the boot and the arm.  Doesnít it??
Arenít the atmosphere, the boot, and the hand in motion are an example of Conservation of Motion all acting together? 
How come JT doesnít mention atmosphere?  It must be me???


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

I have a feeling you guys PmbPhy, Alan, Jeff, and Dlorde know people with real money, maybe even yourselves.?
I really do have a submarine hull design that will go over a hundred mph do spins, flips, like a roller coater... move through water like a knife in soft butter.
I know how crazy this must sound but I also have a sub design that will do over a thousand mph.  However like a dragster, it will not steer well, its speed will only be limited by HP.
I have a design for the fastest aircraft hull.  It will go as fast as any propulsion system will take it, in our atmosphere, No more nose tip resistance!  Look at me the guy whoís always talking about atmosphere, haha.
 
I am willing to put everything I own, "put my money where my mouth is."
If you guys can get me/us in front of an investor(s) we can trust.

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

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

RD

  • Neilep Level Member
  • ******
  • Posts: 7279
    • View Profile
Re: thrust does not work in space
« Reply #142 on: 27/08/2014 09:09:50 »
... I know how crazy this must sound but I also have a sub design that will do over a thousand mph.

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

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

So a 1000mph sub is unfeasible.


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

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

http://www.marineinsight.com/marine/marine-news/headline/how-air-lubrication-system-for-ships-work/
« Last Edit: 27/08/2014 09:49:37 by RD »

alancalverd

  • Hero Member
  • *****
  • Posts: 1349
    • View Profile
Re: thrust does not work in space
« Reply #143 on: 27/08/2014 10:08:43 »

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


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

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

PmbPhy

  • Sr. Member
  • ****
  • Posts: 309
    • View Profile
Re: thrust does not work in space
« Reply #144 on: 27/08/2014 11:53:10 »
Quote from: Reality207
I have a feeling you guys PmbPhy, Alan, Jeff, and Dlorde know people with real money, maybe even yourselves.?
You couldnít have been more wrong.
Quote from: Reality207
I really do have a submarine hull design that will go over a hundred mph do spins, flips, like a roller coater... move through water like a knife in soft butter.
So? Contact the Navy and talk to them.
Quote from: Reality207
I know how crazy this must sound ..
Very much so. Especially I see no way to believe that you already built a life size mockup.
Quote from: Reality207
but I also have a sub design that will do over a thousand mph.
How do you know that? From what Iíve seen so far of your understanding of physics you donít have the ability to design such a hull or predict the performance of a hull design.

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

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

It might caused you problems now or later.

Tell me. Have you ever considered what would happen if to massive objects were separated by a compressed spring and the spring was let to expand? What would happen?
« Last Edit: 27/08/2014 14:15:45 by PmbPhy »


Ethos_

  • Hero Member
  • *****
  • Posts: 532
    • View Profile
Re: thrust does not work in space
« Reply #146 on: Today at 01:18:35 »
Hi guys,
Maybe there is no hope for me :-'(


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

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

If you can't understand this simple principle, there is absolutely no hope.

Reality207

  • Newbie
  • *
  • Posts: 22
    • View Profile
Re: thrust does not work in space
« Reply #147 on: Today at 02:55:17 »
Has anyone ever tired taking a fast jet as high as it can go and at a speed of 300 mph do a dive and accelerate slowly then at 725mph shut the engine off just before passing out haha and crossing the sound barrier in silence?
I know!  But?
What if you equiped the engine with a rotation resister that would allow it to start slowly and dissipate the sound over a great distance, all you would then have to do is accelerate enough to attain positive propulsion before re-crossing the barrier and go zoom with acceptable boom? HaHa,HaHaHaHa
You sure you don't want to see my design?

 

SMF 2.0 | SMF © 2011, Simple Machines
 
Login
Login with username, password and session length