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# Why do people think that rockets work in the vacuum of space?

Fri 26 Apr, 2019 10:12 pm
Why do people say that there is an equal and opposite force from gas movement due to pressure gradient force?
if this were true, the when the wind blows on the back of your head, then you should feel the air in front of you push off your face as it moves away from you.
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Type: Discussion • Score: 2 • Views: 626 • Replies: 25
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farmerman

2
Fri 26 Apr, 2019 10:32 pm
@codec22,
Lex III: Actioni contrariam semper et æqualem esse reactionem: sive corporum duorum actiones in se mutuo semper esse æquales et in partes contrarias dirigi. --Ike Newton

"Mentum bene non est, Lexit est!!!
codec22

0
Fri 26 Apr, 2019 10:42 pm
@farmerman,
That only applies to action/reaction pairs. Is the rocket and gas an action/reaction pair? I don't think so. It is not the rocket that gives the gas momentum, it is pressure gradient force that provides the momentum.
0 Replies

maxdancona

1
Fri 26 Apr, 2019 10:59 pm
@codec22,
We have actually sent rockets up to the vacuum of space, including several missions to the Moon and a several to Mars.

We could explain the physics.... but here we don't have to. Anything that has happened can happen.

The fact is that the rocket and gas are an action/reaction pair.
0 Replies

maxdancona

1
Fri 26 Apr, 2019 11:04 pm
@codec22,
When the wind blows on the back of your head (putting a force on your head from air molecules), the back of your head puts and equal and opposite force on the air molecules. The momentum of the air molecules is changed.
codec22

-1
Fri 26 Apr, 2019 11:38 pm
@maxdancona,
what about the air in front of you? Does't the face give it momentum as it moves away?
maxdancona

1
Fri 26 Apr, 2019 11:58 pm
@codec22,
Are you here to learn? Or, are you here to spread conspiracy theories.

There are correct answers in Physics. Newton's Third Law applies anytime there is a force (including in the vacuum of space). Of course, if you are surrounded by air molecules acting as a fluid, you are going to to get different interactions including a "pressure gradient".

Your biggest mistake is your claim that Newton's third law depends on a pressure gradient (it doesn't). Of course, when there is a force caused by a pressure gradient Newton's third law still applies (since it always applies).

To answer this question, if you face puts force on the air molecules in the front of it, then the air molecules put an equal and opposite force on your face. That is Newton's third law. Of course, whether or not this happens depends on the specific circumstances.

Brandon9000

0
Sat 27 Apr, 2019 12:41 am
When the rocket pushes the burnt fuel backward, the fuel pushes the rocket forward.
codec22

0
Sat 27 Apr, 2019 06:39 am
@maxdancona,
The air around you is bouncing off of you. When wind blows on the bak of your head, shouldn't the wind in front of you push off your face to gain momentum? Why don't you feel it?
codec22

0
Sat 27 Apr, 2019 06:40 am
@Brandon9000,
the rocket doesn't push hot gas out. gases move towards low pressure due to pressure gradient force.
mark noble

1
Sat 27 Apr, 2019 07:29 am
Because they believe what they are told.
Without question.

'Space' is vacuus, but Not a 'vacuum, btw.

And thrust ye, as ye may
On any given day
If thrust ye into empty realms
In empty realms ye'll stay
maxdancona

1
Sat 27 Apr, 2019 09:17 am
@codec22,
You are being silly

Newton's third law says the if air molecules exert a force on the back of my head, the back of my head exerts an equal and opposite force on these air molecules. If you set up an experiment to measure the momentum of these air molecules before and after interacting with the back of my head, you would see that Newton's third law is true in this ciemstance as well.
maxdancona

1
Sat 27 Apr, 2019 09:35 am
@maxdancona,
Just for clarification...

Are you claiming that rockets don't actually navigate in space (in spite of the fact that they do)?

Or are you claiming that rockets do navigate in space, but that the basic laws of Phyisics don't apply?
mark noble

0
Sat 27 Apr, 2019 10:06 am
@maxdancona,
Is that question directed at me, Max?
?
0 Replies

farmerman

1
Sat 27 Apr, 2019 10:39 am
@mark noble,
sorta like the rules and obsevations in the bible are unquestioned by others
mark noble

0
Sat 27 Apr, 2019 10:52 am
@farmerman,
Exactly the same.

Even yourself, Fm - You take a geode and match it to a chart, somebody else designed, and you have unquestioning faith in that 'chart'.

It is as it is.

All's Well:)
farmerman

1
Sat 27 Apr, 2019 11:03 am
@mark noble,
I think your mind is on the simple track. Geodes dont need no steenkin "charts" (Obviously even you know what they are). Looking inside one is always unique original research, no matter what one is seeking. Following the Bible and INTERPRETING it with **** that was never said within its covers is what science deniers do.
A rocket engine acts as a UNIT. The explosion occurs within the chamber and is directed out the nozzle via a Bernoullean orifice. The entire reaction energy is focused through a single nozzle and the newtonian reaction is to propel the entire rocket UNIT in the opposite direction. Surely yoou are joking eh? Cuz if you aint, I think weve discovered your problem

mark noble

0
Sat 27 Apr, 2019 11:36 am
@farmerman,
It was a 'grounded' analogy.

I'll try another...

When did the permian extinction event occur, in mya?
0 Replies

Brandon9000

0
Sat 27 Apr, 2019 10:30 pm
@codec22,
codec22 wrote:
the rocket doesn't push hot gas out. gases move towards low pressure due to pressure gradient force.

Actually, most of the force is supplied by expanding gases from a chemical reaction. That causes most of the pressure which you speak of in the combustion chamber. It's not tremendously obvious, but somewhere in the process, some part of the gas pushes on the rocket and the rocket pushes back. This is literally, the only reason the rocket moves - conservation of momentum.
0 Replies

Brandon9000

0
Sat 27 Apr, 2019 10:33 pm
@mark noble,
mark noble wrote:
Because they believe what they are told.
Without question.

'Space' is vacuus, but Not a 'vacuum, btw.

And thrust ye, as ye may
On any given day
If thrust ye into empty realms
In empty realms ye'll stay

Can you turn this into some sort of coherent assertion and argument or is it just a muddle of nonsense?

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