Hey Papa,
You know that page you copied Newton's 3rd law from;
http://www.physicsclassroom.com/class/newtlaws/Lesson-4/Newton-s-Third-Law
Well, further down there's an exercise;
2. For years, space travel was believed to be impossible because there was nothing that rockets could push off of in space in order to provide the propulsion necessary to accelerate. This inability of a rocket to provide propulsion is because ...
a. ... space is void of air so the rockets have nothing to push off of.
b. ... gravity is absent in space.
c. ... space is void of air and so there is no air resistance in space.
d. ... nonsense! Rockets do accelerate in space and have been able to do so for a long time.
Click on the "See answer" button and you get the following;
Answer: D
It is a common misconception that rockets are unable to accelerate in space. The fact is that rockets do accelerate. There is indeed nothing for rockets to push off of in space - at least nothing which is external to the rocket. But that's no problem for rockets. Rockets are able to accelerate due to the fact that they burn fuel and push the exhaust gases in a direction opposite the direction which they wish to accelerate.
You're using a source that says rockets work in space to bleat about rockets not working in space! How ironic...
Oh snap, well done! I don't know if Papa can even get out of this.
The original quote on N3 was mine.
http://www.physicsclassroom.com/class/newtlaws/Lesson-4/Newton-s-Third-Law
I don't think Papa checked the source at the time he copied and pasted it, or the ninety nine times after that.
Papa I spent a goodly portion of my Sunday brushing up on thermodynamics and gas laws, could you perhaps point me in the right direction? All the sources I've found lead me to believe rockets will work in a vacuum, free expansion of gas will not stop the rocket from working.
The thing is the rocket is there (stopping the gas expanding in that direction so "free expansion" doesn't happen on account of the gas hitting the rocket...
But I'm no chemical engineer.
If you made yourself a man sized rocket and wanted to put it onto your roof but to get it up to your roof, you have to put your head inside of it so you can use your hands to grip the ladder.
Let's call your head and body, the fuel pushing against the inside of your rocket. Your ladder has rungs for your legs to step onto and up. The rungs provide the resistance to your push of your legs to allow you to keep that rocket moving upwards.
Your legs are the energy that pushes on the rungs to propel you and your rocket onto the roof.
In real rocket workings, it would be the fuel compressing against the atmosphere with the atmosphere being the rungs of your ladder, against you and that rocket you are under.
Now take away the rungs of the ladder and try your best to get that rocket onto the roof. You can't because your energy is basically allowed to exit the rocket with no work done to push that rocket in the opposite direction. This would be known as space, or the vacuum, or basically the free expansion of matter ejected from the rocket nozzle.
You need a resistance for a rocket to work. It cannot work by just pushing on itself without an external resistance to that push. Atmosphere provides this.
Some people have different ideas of how free expansion works. The truth is, there's no such thing as free expansion in its entirety. There's always a resistance. However, the resistance can be so weak as to be rendered as good as free expansion. Basically this is an extreme ultra low pressure environment - or to put it more plainly, space as we are told it is.
The simple thing is, if we have close to free expansion of any matter ejected from anything, then you cannot have a reactionary resistance to the expanded mass inside your container/rocket, or whatever.
Poll