What does a rocket push against in space?

You say I dont understand!
I dont think most of you Dont understand.
"Every action has an equal and opposite reaction."
Yes but you dont have any thing is space to push on.
all you do have is a explosion out the back.
that can only push on its Self !
that dose not seem very much to move a
lets say a 5 ton rocket.

All most of ATS do is just say people are Stupid !
and hope they go away. well fruit to you.

some one tell me how much force would be
applied against a 5 ton rocket from a truster?
YES I know over time it will build up
and yes I know All about sling shot
orbits around moons and planets.

stop saying "Every action has an equal and opposite reaction."
like a Parrot!like its the meaning of the Universe.

Geez. Ok.

If I am in space. And I throw a baseball, I have ejected a few grams of mass from my body. That ejection of mass propels my body in the opposite direction of the baseball.

The amount of force that is applied to my body is the same amount of force that I imparted to the baseball. But the force is applied to my body in the opposite direction of the baseball.

Since I'm in space, I'm weightless, so I am merely trying to move mass with mass. I can move my own body if I start by floating in space with a backpack full of baseballs. As I throw baseballs away from me, I push myself through space by ejecting the mass of the baseballs. Since Force has a mass component and an Acceleration component (F=MA), then the faster I can throw the ball away from me, the more force I apply to my body, opposite the direction of the baseball.

For a rocket, It's full of rocket fuel. If I shoot rocket fuel out the back end of a rocket, I am moving mass really fast out in one direction, so the rocket moves away from the ejected rocket fuel with the amount of force that was generated by ejecting the fuel. The more reactionary (explosionary) the fuel, the faster it comes out the nozzle of the rocket and thus, more force is applied because the acceleration is higher.

a reply to: Hellas

utter bollox

a reply to: ignorant_ape

Any ignorant person can create video for other ignorant persons to watch and believe.

Pushing against the air ... really? We've visited that fail here.

a reply to: Hellas

The video comments are full of ignorant stuff.

a reply to: HellasThe feather in the video DID move. Plain as day for anyone watching closely. In fact it moved in a direct and measurable proportion to the amount of gas contained in the chamber for the fan to act on.

Thanks for the visual proof of Newtons laws of physics!

a reply to: Hellas

But what does this fan set-up have to do with rocket thrust? Nothing.

In this experiment, the air in the chamber (when the chamber contained air) would be the fan's propellant -- i.e., the air is what is being propelled by the fan blade, creating a reaction.

When they took all of the air out, they removed the fan's propellant.

However in the case of a rocket, it still has propellant (rocket fuel) even when it is in the vacuum of space.

Therefore this experiment is not at all analogous to a rocket in space. I have a feeling the person making the video actually knows this, and is just intentionally trying to put one over on people.

Eleven flags? ????? Really???????
There are almost a dozen people on the his thread with such lack of elementary basic physics ????

What will become of our species?

VF

a reply to: buddha

You very much are, we have given you everything including answers and pictures that a 6 year old could comprehend and understand.

The thrust pushes against the body of the craft - not the body of space - it is the same on Earth.

How do you think a thrust pack on the back of an astronaut works?

a reply to: buddha

You say I dont understand!
I dont think most of you Dont understand.
"Every action has an equal and opposite reaction."
Yes but you dont have any thing is space to push on.
all you do have is a explosion out the back.
that can only push on its Self !
that dose not seem very much to move a
lets say a 5 ton rocket.

Highlight of your quote by me.

That statement there by you is showing where your confusion is I think.

Take a look at Newton's statement again:

"For every action, there is an equal and opposite reaction."

Notice the word I highlighted: Opposite.

When I fire a gun, the gun will kick back. It's not doing it because it's pushing on the air.

It's doing it because of the bullet and gas leaving the barrel of the gun and very high velocity.

The more mass, and higher velocity the bullet and gas, the more the gun will kick back.

Take away the bullet (just a blank round) and the gun will still kick with the high velocity exit of the expanding gasses.

If you set the gun up in a vacuum chamber, hanging by rope and remotely trigger it, you can see it kick back when the gun fires.

It does this because it's suspended and the force of the gases exiting the barrel will cause this reaction (which is opposite in direction of the exiting gases).

Even jet engines work this way. The amount that they "push" on the air is not enough to move the air craft. The density of our atmosphere is no where near thick enough for that. The reason a jet engine works is because of Newton's 3rd law: the high velocity thrust from the engine is what propels the aircraft forward, because physics says that there must be an opposite reaction to that thrust.

You do not have to take our word for it. You can do the experiments yourself. May people in school do, as with other things to see physics in action.

I'd say the confusion arises when thinking in relation to how wings, propellers, turbine fans etc operate in the atmosphere IE they create a pressure differential on either side of the impeller (or wing) which produces the lift or thrust in the desired direction.

Rockets are somewhat different in that a high pressure is produced in a container and allowed to escape in a controlled directional manner which produces a net force opposite to the direction of the escaping propellant. The 'pushing' is against the inside wall of the rocket engine itself and atmosphere actually impedes a rocket's performance due to the drag (proportional to V^2) which doesn't happen in a vacuum.

It's own inertia.

originally posted by: buddha
You say I dont understand!
I dont think most of you Dont understand.
"Every action has an equal and opposite reaction."
Yes but you dont have any thing is space to push on.
all you do have is a explosion out the back.
that can only push on its Self !
that dose not seem very much to move a
lets say a 5 ton rocket.

All most of ATS do is just say people are Stupid !
and hope they go away. well fruit to you.

some one tell me how much force would be
applied against a 5 ton rocket from a truster?
YES I know over time it will build up
and yes I know All about sling shot
orbits around moons and planets.

stop saying "Every action has an equal and opposite reaction."
like a Parrot!like its the meaning of the Universe.

Here is the math if you truly want to learn

www.grc.nasa.gov...

The idea that rocket propulsion wouldn't (or even "shouldn't") work in space is right up there with "heavier-than-air flight is impossible" in the ranks of scientific statements that were later proven completely wrong. It must be about 100 years old in all, and it's one of the reasons that the Allies didn't have rocket technology while Nazi Germany was raining V1s and V2s down on London.

It led to this newspaper correction, which is still regarded as one of the all-time classics in the genre:

JULY 17, 1969: On Jan. 13, 1920, Topics of The Times, an editorial-page feature of The New York Times, dismissed the notion that a rocket could function in a vacuum and commented on the ideas of Robert H. Goddard, the rocket pioneer, as follows.

"That Professor Goddard, with his 'chair' in Clark College and the countenancing of the Smithsonian Institution, does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react -- to say that would be absurd. Of course he only seems to lack the knowledge ladled out daily in high schools."

Further investigation and experimentation have confirmed the findings of Isaac Newton in the 17th century and it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error."

See the dateline on that correction? Not only was it just under 50 years since the erroneous statement was published, it was the second day of Apollo 11's journey to the Moon.

a reply to: audubon

the ghosts of goddard and parsons say - you are talking utter bollox

a reply to: ignorant_ape

Really? Oh, OK.

a reply to: buddha

There is not nothing in front just very little particulate mass, space is not empty.

The expanding gasses push against the engine outlet and vehicle itself to achieve forward thrust/momentum.

Point of fact there is not enough mass in our universe to achieve/sustain travel from one star to another utilising conventional methods of propulsion.

originally posted by: audubon

See the dateline on that correction? Not only was it just under 50 years since the erroneous statement was published, it was the second day of Apollo 11's journey to the Moon.

I bet the very late retraction of the 1920 article was all intentional and part of their coverage of the Apollo 11 flight.

The paper could have been looking back at the history of spaceflight (which would be a natural part of their coverage of the first manned mission top the Moon), and took notice of their 1920 article saying spaceflight was impossible, and felt it was relevant to write a retraction, albeit a late retraction.

So I see nothing strange about the 50 year-old retraction.

a reply to: buddha

technically you could test this yourself , create a vacuum chamber large enough to host a small scale model rocket that works

then test it yourself and see how rockets work in vacuum

its achievable I mean if "seeing is believing " is your thing then have at it