The Naked Scientists

The Naked Scientists Forum

Author Topic: How do rockets in space propel themselves?  (Read 13986 times)

Offline bizerl

  • Sr. Member
  • ****
  • Posts: 279
    • View Profile
Re: How do rockets in space propel themselves?
« Reply #25 on: 13/09/2012 11:19:59 »
waytogo - you seem to be struggling with this concept.

Consider two identical cubes, each with an open face, floating in the "vacuum" of space. In the open face are two identical astronauts of identical mass, with their feet attached to the cube. The cubes are side by side so that the open faces are together and the astronauts are face to face.

They push against eachother. The two cubes fly apart from the original position at the same speed.

One of the astronauts then turns around and picks up a bowling ball that was in his cube (don't worry, the other cube had one as well :). he holds it in front of him and since there is no gravity and they are both moving at the same speed in the same direction, the bowling ball remains in front. He pushes on the bowling ball and while the bowling ball flies away, the cube also increases it's velocity away from the direction of the ball.

You can see where this is going. If you then pushed out some sort of gas, then it would push the vessel a bit further. Because gas molecules are generally smaller than your average rocket, you need to push lots out, really fast. This is essentially what rockets burning fuel in a vacuum do.

I think.

Also, consider the recoil of a gun. If you could somehow rig up a gun so that it could fire in the vacuum of space, there would still be a significant recoil from the bullet being pushed out at such high speed.

I personally don't have the means to conduct such experiments to prove such points myself, but I'm happy to go along with mainstream science on this one and just do the thought experiments on basic principles.

waytogo, I hope that helps you understand it a bit better, and everyone else, please correct me if i've over-simplified it.
« Last Edit: 14/09/2012 07:48:51 by bizerl »
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11993
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Re: How do rockets in space propel themselves?
« Reply #26 on: 13/09/2012 18:43:25 »
I think of it as imbalance Imatfaal, and so also an expression of entropy :) although in the fast lane :)
To me it has to do with 'symmetries' too in some ways as the situation clearly is non-symmetric, if we define it to a 'system' . But then again, in real life it's also a 'open-ended' system but using way2gos ideas of a tank having a vacuum we get a nice system. Anyone wanna buy one? And a rocket.
 

Offline waytogo

  • Full Member
  • ***
  • Posts: 68
    • View Profile
Re: How do rockets in space propel themselves?
« Reply #27 on: 21/11/2012 11:23:57 »
Sorry but needs simple facts, not words only.

So, just put in a vacuum chamber that mini rocket:

It's curious how there is not a simple educational stuff on school labs to prove that... don't you?
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: How do rockets in space propel themselves?
« Reply #28 on: 21/11/2012 14:52:05 »
Sorry but needs simple facts, not words only.

So, just put in a vacuum chamber that mini rocket:


Do you really doubt that a rocket could work in the void, I mean, seriosly? If the answer is yes, you need some holidays in a quiet place for some time...
 

Offline waytogo

  • Full Member
  • ***
  • Posts: 68
    • View Profile
Re: How do rockets in space propel themselves?
« Reply #29 on: 21/11/2012 15:06:44 »
Do you really doubt that a rocket could work in the void, I mean, seriosly?
I would to see a scientific stuff (demonstration) about that (however, I'm not the only one). I wonder why there are not any stuff in schools lab to study the behaviours of that physics at all relative to Vacuum Environment concerning action/reaction relative to gas engines?

If the answer is yes, you need some holidays in a quiet place for some time...
Do I Have to Answer That?


Thanks  ;D ;D I've always wondered that...

Me too.  ;)
« Last Edit: 21/11/2012 19:55:21 by waytogo »
 

Offline Don_1

  • Neilep Level Member
  • ******
  • Posts: 6890
  • Thanked: 7 times
  • A stupid comment for every occasion.
    • View Profile
    • Knight Light Haulage
Re: How do rockets in space propel themselves?
« Reply #30 on: 21/11/2012 15:35:39 »
Being a rocket scientist (not) I too had some trouble with the concept of how a rocket could work in space, until I was shown the light (and kicked up the bum).

Whether your rocket is in space or in Earh's atmosphere is no different (I think). The thrust produced by the rocket pushes both ways. In Earth's atmosphere, the rocket would be subject to friction, but in space, it would not. So as I understand it, less thrust would be needed in space than in the atmosphere.

So in Earth's atmosphere the thrust would produce (O represents the point of thrust)

<<<<O>>>>

But due to friction would result in

<<<O>>>>>

While in space it would result in

<<<<O>>>>

ie, equal thrust both ways with no friction. Both the gaseous exhast and the rocket move appart at the same force. The only difference is that the point of thrust moves with the rocket and you can see the rocket move, but not the gaseous exhast.

I think that's about right, though my explanation probably leaves much to be desired.

If I am wrong, bugger it.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: How do rockets in space propel themselves?
« Reply #31 on: 22/11/2012 19:01:52 »
Do you really doubt that a rocket could work in the void, I mean, seriosly?
I would to see a scientific stuff (demonstration) about that (however, I'm not the only one).
This would have a meaning if you had never heard of a real rocket going in the void, but you have...
Or you think that some rare atom around could make the difference?

About an experiment, they have already told you: stay in a chair with wheels and little friction with pavement, then throw away something heavy enough: you will go in the opposite direction ("action-reaction" law or "third principle of dynamics"). Where do air enter into the effect?
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: How do rockets in space propel themselves?
« Reply #32 on: 22/11/2012 19:05:54 »
If the answer is yes, you need some holidays in a quiet place for some time...
Do I Have to Answer That?
It would help me understand if you are serious or if you are just kidding us.
 

The Naked Scientists Forum

Re: How do rockets in space propel themselves?
« Reply #32 on: 22/11/2012 19:05:54 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums