Is the Unisverse really expanding?

[Nightshift]

Now we all know about the ever expanding Universe confirmed by the Redshift theory, but, I can't figure out the following.

The Unisverse refers to all that is, including the vacuum of space itself.

If the space between matter is a consistant vacuum (which it most likely is) and our feeble atmosphere is in equilibrium with the earths gravity and this vacuum and presumably stable and fixed (for all intents and purposes), and, the Unisverse is expanding outward it is fair to presume the void or vacuum is expaing out with it, if this is so then why does the vacuum not increase in it's intensity and draw the atmosphere from our planet (and others for that matter) while our gravity remains constant? (I for one am glad my question has an answer but I just don't know the answer)

Anyone???? :confused: :confuse3: :P

[Starkler]

A vacuum in itself doesnt apply a force in that there is no such thing as suction. What we call suction is caused by a greater air pressure exerting a force on an area of lesser pressure.

A vacuum is a vacuum meaning a space with nothing in it.
A vacuum cannot 'increase in intensity' as you cant have "less than nothing" in a given space.

I hope this makes sense and answers your question.

[Nightshift]

Nup, still don't get it, sorry.

You refer to the term "Vacuum" which is defined as, "Latin, empty space, from neuter of vacuus, empty, from vacre, to be empty." but I refer to the actual void which is outside our atmosphere which when introduced to a higher pressure atmosphere absorbs it with gusto therefore displaying a void of lesser pressure, thus a vacuum in the negative atmoshpere sense. The void of space can not be nothing, if it were, rocket engines would not produce thrust, a high pressure ejection creating movement based on a lower pressure on it's opposite side? I still think the negative pressure of this void (vacuum) should be increasing towards the negative, unless, the universe has a fixed volume suggesting it is contained? I prefer to think of the universe as absolutely infinate without boundaries, of course my feeble Meade only see's a few million light years at best so I may be wrong.

More input requested.

[janoskiss]

Yes.

[slice of heaven]

The universe isnt 'infinite'. It actually has boundaries.(so the theory goes)
Who and how they worked it out, dont ask me.

You cant have less than nothing in a space unless you remove the space itself. Remove the space and youve also removed all sense of time related to that space, past, present and future.
So even though it was there, it never was.
Crazy stuff hey

Space doesnt have a negative pressure unto itself only in relationship to positive pressures like our atmosphere.
So the vacuum of space is 0 pressure and our atmosphere has a positive pressure from the atmospheres mass pressing down on the surface.

[mojo]

A rocket doesn't 'push' against air, it pushes against itself. Rocket fuel burns, gases expand, expanding gases come out at high velocity, momentum changes producing thrust. All a rocket is doing is shifting its mass in the opposite direction of it's travel. The hot expanding gases push on the rocket and the rocket pushes on the gases... which is why a rocket works in a vacuum.

[ballaratdragons]

Nightshift,

My version of the theory of Rocket propulsion in a void:

An analogy-

If you could open the window of a spacecraft and spit, the spit as it comes out in one direction would actually push you in the opposite. The spit does not hit and push against space as there is nothing to push against. It is the separation of the spit and your mouth at pressure that pushes them apart.

Try this for an experiment. Go outside and sit down on the ground. Throw a rock or something else. Do you feel your body being forced (moving) in the opposite direction? Now imagine that force without Earths air pressure. If you threw a rock in space you and the rock would zoom off at an amazing pace in opposite directions. The harder you throw, the faster you go.

It is not the Earths air pressure on the rock pushing you backwards. It is just two objects pushing each other apart, not one object pushing on space. If it were up to air pressure, then the objects would face resistance and actually not move as far or as fast!

They can actually propel and steer space vehicles with those small soda fountain canisters you buy in the supermarket.

A can of fly spray could make a space vehicle change direction many times before the can ran out of fly spray.

I think that is enough analogies.

[Starkler]

Heres a question.
Considering the laws of momentum and the conservation of mass, does burning rocket fuel in a vacuum achieve any greater thrust than simple squirting the same mass of propellant out the back of the rocket without igniting it ?

[slice of heaven]

That depends on the exit velocity of each.

[ballaratdragons]

Interesting question Geoff. Hope someone in here knows the answer.

I may take the liberty of having a guess and see if I am close.

Maybe the extreme heat of a thruster gives better opposition reponse in the extreme cold of space.

Or maybe a fuel burning thruster gives more opposition blast force than say the force given by the simple release of a compressed gas.

[mojo]

Mass x Velocity
i'd say so.
if you could squirt out the propellent fast enough. but then you'd have to work out a way to squirt it out fast enough without using more energy to do it.

but i suppose if you burn less mass at a time but let it escape very very very fast, through the bottom of the rocket, it would acheive the same effect without wasting energy on building gigantic squirters :)

that is, you would need to also carry fuel for the gigantic squirters that spit out unburnt propellent. burning it is just so much more efficient...

[Starkler]

Yep thats the answer . Igniting it creates the velocity for that fuel mass to generate the momentum. I was having a blonde moment .

[slice of heaven]

The thrust equation is a bit more complicated than that.
But in a nutshell
The amount of thrust depends on the mass flow (Starkler said the same mass) and the exit velocity of the exhaust.

[ballaratdragons]

Cool.

That means Mojo and I intellag ... inttellig ... clever!

I would imagine that the blast force out of a pinhole would be much more than out of a 1" hole.

[slice of heaven]

BD
To answer your last statement ,NO, unless youve got an extremely tiny rocket.
The exhaust nozzle size is taken into account in the thrust equation as well.

[ballaratdragons]

LOL, Slice that was meant to be an example of thrust exit size/thrust pressure.

I didn't mean they would use a pinhole size blast exit.

Similiar to a fighter jet when it closes down the exit size to gain more thrust.

[slice of heaven]

The answer is still no. The tiny rocket part was a joke. lol
I might do a search after and try and find a full detailed description of the thrust equation to explain it.
I used to play with model rockets when I was a kid and it is easy to understand.
The size of the exhaust nozzle is critical.
Never had a toy jet though. But i think the adjustable exhaust nozzle on the jets is for the afterburners. They are opened for the afterburners and closed for the normal operation. The afterburners are only a series of injecters squirting fuel directly into the exhaust ,therefore needing a larger exhaust nozzle.

[ballaratdragons]

RFLMAO!

I'll just keep quiet. :P

[Nightshift]

You've all had a good stab at it but not one of you has explained the rocket, a thrown rock transfers kinnetic energy from itself to the thrower in the form of enertia, not thrust, the thrust is created by the thrower, not the rock. Someone important to this arguement once said, "For every action, there is an opposite and equal re-action", which when applied to your rocket in a vacuum theory doesn't work. The gases do indeed puch against the rocket engine propelling it forward, but, as we know, in a vacuum there in no resistance to thrust and therefore a rocket would not move based on this principal, it moves not because it created thrust but because the pressure behind the engine is greater than that in front of it, oh, by the way, if insect spray could propel a rocket with any deliberation NASA would own the Mortein company, instead, they prefer to spend billions engineering propellants. Slice of Heaven, don't believe the Universe has a boundary because some theorist wrote it in a white paper, believe it because you know it to be true or question it, it wasn't that long ago that someone wrote a white paper on how the earth was flat and sailing near it's boundary would result in doom. To believe the vacuum of space is zero pressure in relation to our atmosphere then you would have to have knowledge of other atmosphere's that must be more negative than zero? It is just as conceivable that space is a negative vacuum as it is that our atmosphere is a positive one, to argue otherwise would be egocentric, the earth and it's atmosphere are not unique as much as we would like to think it is, our atmosphere is not a yard stick by which we should measure the pressure of space, perhaps the pressure of space (space being a tad more substantial than our little rock) is a yard stick by which we measure the pressure of our atmosphere? I'll keep an eye on this thread. :confuse2:

[mojo]

I think you need to understand the principles of conservation of momentum to understand why a rocket moves. Atmospheric pressure has nothing to do with it.

To simplify the logic: The rocket moves exactly for the same reason that if you were floating in space and threw a rock, you would move in the opposite direction. The propellent is the rock, the person is the rocket. The rocket throws propellent and moves because the propellent pushes against the rocket in the opposite direction.

If you wanted to, you could indeed use mortein to launch a Saturn V rocket, but it would be far more expensive, has far less energy than liquid oxygen, and kill far too many people as it lifts off :)
You can use anything as propellent. Propellent is just the 'stuff' you're throwing away to shift momentum.

[ving]

cool! science experiment time!! :D

you need:
1 pingpong ball
1 straw
1 3" diameter pvc tube or other similar tube

place the ball on a flat surface and blow thru the straw at it, taking note at velocity achieved at lung presure exerted. now grab the 3" tube and repeat useing the exact same pressure.
the force coming out of the 3" tube is substantially less than the straw and the ball moves less.

Dr Ving says lesson over.
interestign topic peoples! :)

[ballaratdragons]

David,

Astronauts don't carry straws, ping-pong balls etc. LOL

Be funny to see an Astronaut wind down the window of his shuttle a blow through a straw to make a course correction.

[slice of heaven]

To add to that Ving
Get 50 people blowing through the same straw and 50 people blowing through the 3" tube.
Now which will move the ball more?

[ving]

50 people on one straw! now your just being silly! :rolleyes:
now if the straw had 50 entry points so 50 people could use it.... I'd still say the straw would win. of course you cant get 50 peeps on the one hole (even on a 3" pipe!).

hey ken... I think you are on to something there!

[slice of heaven]

Nightshift

Laws 2 and 3 apply to the rockets thrust.

What other tangible 'yardstick' can we use for pressure thats relative to us living on Earth.We do use the pressure of space to compare our atmospheric pressure. And the pressure in space is zero.

Its all theory. Until you can actually show something factually it is theory.Even the end of our Universe has to have a boundary.Whether its finite or infinite. Its a debate that will continue for all time ,until it is actually proven.
All theories relating to the size of the universe have had to have other unproven theories added to make the original theories plausable. So theres a lot of assumptions being made, not proven.
To reverse the situation; Is there a centre of the Earth?
I could say no!
Travel to the centre of the Earth and put a dot there. Then halve that dot, then halve that dot, then halve that dot, then halve that dot and you can do that infinitely.So no there is no centre of the Earth.
But there is a centre of the Earth. The term infinity itself suggests boundaries. Aristotle explained this better than I can.
Whichever train of thought you wish to follow will ultimately bring you to the conclusion that the answer cant be proved or disproved.
In a truly infinite universe youll have an infinite number of everything, including dimensions. So in other dimensions you'd possibly have other universes. So if there's other universes there would have to be a boundary between this universe and the others so therefore the universe isnt infinite.
So an infinite universe is a contradiction to itself.
Just because we cant see the edge of the universe doesnt mean there isnt one.
By including space in your description of the universe youve also placed the constraint of time as well. You cant have one without the other.

[slice of heaven]

Sorry Ving, I'm always silly on Monday mornings.

Heres a simple diagram to explain rocket thrust

http://www.grc.nasa.gov/WWW/K-12/airplane/rockth.html

Exhaust nozzle size matters

[ballaratdragons]

In the link above the 'Nozzle Simulator' helps.

[slice of heaven]

I didnt even look at the page BD. I just seen the pic and equation and posted it.
Run the Ving straw theory it through. lol

[ving]

hmm... i did. my it seems that the "throat size" is a case of the bigger the better too.... gah! stoopid jet thing!