How does a rocket work in a vacuum

[Nink]

It does appear that you are really not interested in how a rocket can work in space.  You only want to try and convince others it can't.  Sorry, but I am not going to fall for that and I don't think anyone else will either.  I am done here.

Carroll

I agree a square cardboard box the same size as the brick is lighter than a brick so the mass is lower but the air pressure against the brick and the box is the same. I think we are mixing concepts. One is pushing against the brick and ignoring the friction caused by the atmosphere and the other is pushing against the atmosphere and discounting the mass of the object.   We could reverse this and say a large sheet of cardboard that weighs less then a brick is pushed outwards while standing on the skateboard. This will force me to go further in the opposite direction  then if I was throwing the brick of a heavier mass.

[Nink]

Nink:

The gas IS the mass.
The FASTER you can expel it the harder it pushes the rocket.
The MORE gas you expel the harder it pushes the rocket.

Nothing else is required.

Unfortunately the gas can not be the mass as we are trying to move that very same mass upwards as we expel a small portion of that mass downwards. Your theory is that we are releasing a small portion of this mass and then pushing against this mass in vertical direction directly opposite to the force of gravity. I think we did the math for this under the recoil idea with Yosemite Sam firing bullets at the ground.

[citfta]

I agree a square cardboard box the same size as the brick is lighter than a brick so the mass is lower but the air pressure against the brick and the box is the same. I think we are mixing concepts. One is pushing against the brick and ignoring the friction caused by the atmosphere and the other is pushing against the atmosphere and discounting the mass of the object.   We could reverse this and say a large sheet of cardboard that weighs less then a brick is pushed outwards while standing on the skateboard. This will force me to go further in the opposite direction  then if I was throwing the brick of a heavier mass.

Without realizing it you now have the concept.  The rocket is not pushing against anything except the exhaust it is pushing out the back.  Exactly the same as you pushing against the brick when you throw it hard.

Carroll

[Nink]

Without realizing it you now have the concept.  The rocket is not pushing against anything except the exhaust it is pushing out the back.  Exactly the same as you pushing against the brick when you throw it hard.

Carroll

Hi Carroll,

In the example I gave with the sheet cardboard when I push the cardboard against the atmosphere the cardboard pushes back against me as a result of the molecules in the atmosphere on the opposite side of the cardboard. When I push on the cardboard I am leaving the cardboard behind and pushing off the cardboard. If I hang onto the cardboard it will exert the same force when I try to move so I need to either re orientate the cardboard to reduce the size of my force against the atmosphere or get another piece of cardboard and leave the old one behind. 

This is all great on earth where we are not in a vacuum.   In a vacuum we have no air for the cardboard to push against.  We push the cardboard out in space nothing will happen if I hang onto it. Even if I re orientate it and repeat I still will not move.  If I throw the cardboard out away from me I will move in the opposite direction of the cardboard but the mass is what will determine the distance I move and not the air resistance created by the size of the cardboar.d

If I push on very same sheet of cardboard in space it will not move me further than a solid brick of the same mass as the sheet of cardboard moves me. Our momentum is determined by the mass of the cardboard and not the air resistance produced by the cardboard.

If the gas is what is causing me to move the gas has to push against something. in the absence of atmosphere there is nothing for the gas to push against.

Hopefully this video will explain why this is not the case.  https://www.youtube.com/watch?v=AfVfsnL-zbo
 

[lumen]

Strange.