What does a rocket push against in space?

Has any one calculated how much fuel you would
need to accelerate then decelerate to get to mars?

my point is a rocket in earth atmosphere
has some thing to push against.
But in the vacuum of space you have Nothing to push against.
Only the Gas the rocket pushes out the back!

think about that. when it starts it has nothing at All to push against.
and then as the gas builds up behind it. it will push against that.
So all the weight of the rocket is pushing against a Tiny mass of gas.

Please comment, I would like to know!

a reply to: buddha

Had you ever considered the possibility of the gasses expansion actually "pushing" against the inside of the engine as it is allowed to escape out the rear.

The thrust actually is measured against the motor.

a reply to: buddha

There's nothing in front of it to slow it down so once its going it'll just carry on until there is.

Someone else will explain it in better words than mine but that's my understanding of these things.

originally posted by: tinymind
a reply to: buddha

Had you ever considered the possibility of the gasses expansion actually "pushing" against the inside of the engine as it is allowed to escape out the rear.

The thrust actually is measured against the motor.

YES!
bus the gas has very low mass.
and it would be moving away from the rocket.
so it could not push on it much.

so the rocket would only push on a little gas at the back.
compare that to the mas of the ship?

Only the Gas the rocket pushes out the back!

Answered your own question.
Don't worry, it's not NASA

a reply to: buddha

I know!

Wow. Is this going to be rockets in space are actually a hoax?

when the rocket turns and fires the rockets to slow down.
the gas will NOT slow down, it will shoot away at full speed.
as its in a vacuum.

so the rocket can not use that gas to push against to slow down!
is would just shoot off into space.
Yeas a very little of the gas would slow the rocket down a very little.
but a rocket Needs some thing to push against.
a rocket of 5 ton would need just over 5 ton to push against to slow down.

a reply to: buddha

CHECK THIS OUT

The hot exhaust gas flows through the rocket nozzle and is accelerated to the rear of the rocket. In re-action, a thrusting force is produced on the engine mount. The thrust accelerates the rocket as described by Newton's second law of motion.

Hope that helps you understand this a bit better.

bus the gas has very low mass.
and it would be moving away from the rocket.
so it could not push on it much.

force is mass and acceleration, not just mass.

Newton's third law of motion

originally posted by: roadgravel

Wow. Is this going to be rockets in space are actually a hoax?

You and I both know it is.

Itself

Yep, what the rocket is "pushing" against is literally the gas coming out of its nozzles not the air, even when it's in the atmosphere. The gas expands, builds up kinetic energy and rushes out the nozzle, and the rocket is pushed the opposite direction. It's the whole "Equal and opposite reaction" thing. Kinda how if you threw a baseball from a complete standstill in space your body would start moving slightly in the direction opposite the direction you threw the ball.

"Every action has an equal and opposite reaction."
a rocket in a atmosphere pushes on the atmosphere.
a rocket in the vacuum of space pushes
on the atoms of the gas it fires out the back.
atoms have a very low mass.
that is not enough to move a 5 ton rocket much.

Nothing to do with hoax!
I just find it odd.
some one else will USE it for hoax.

its like saying if you have a car in space it will move!
a car needs a road, a rocket Needs some thing to push against.

originally posted by: roadgravel
Newton's third law of motion

Humans never figured out how to get anywhere without leaving something behind

a reply to: buddha

The combustion creates a tremendous amount of force (enough to move rockets due to their weight); for every action there is an equal an opposite reaction (Newton's third law): the combustive force pushes out of the back of the rocket, and the opposite reaction is the rocket moving forward. There is no friction in space so the rocket can move at more or less constant speed (not requiring a constant supply of fuel) unless something slows it.

But in the vacuum of space you have Nothing to push against.

The rocket creates that by virtue of the force it creates through combustion.

Yes rocket use earth to build up speed to leave earth.
sling shot around earth then the moon.
but in deep space there is NOTHING Vacuum.

Just giving something as a messenger.

The lower part of the rocket pushes the upper part, and the upper part is like the front of a ship going through the sea. It's the same in space and on earth, only in space there's no atmosphere so speed (and mileage) may vary. Meaning it's unexpected, because it's unknown.