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First, I (as I suspect just about everyone here) understand that rocketry DOES indeed work in a vacuum. But I have some free time on vacation and saw this post bumped
https://www.rocketryforum.com/showt...y-Doesn-t-Work-in-the-Vacuum&highlight=Vacuum
And thought what the heck, maybe it will be fun . I know....I need to get out more.
Anyway, these guys take a certain amount of science and layman's thinking and try to contradict the science of Rocketry in general and NASA in particular.
In any case they raise some legitimate questions and for the most part are polite. In reviewing the posts I find a tremendous misunderstanding if what a vacuum is (and more importantly IS NOT!). Some of the concepts I think I may need a bit of help to answer. I will not claim to represent THE ROCKETRY FORUM, so if I make mistakes it will not reflect on our Forum. I do think some of these questions may also be educational for newbees (and some oldsters on our forum, hence posting here.)
question 1
While I do no doubt the fact at action/reaction is sufficient and certainly the dominant force in rocket propulsion, DOES the presence of air (mass) behind the rocket have any effect, positive or negative, in the degree of force generated (does is provide any additional "push"). One of the examples used in ClueForum was a jet ski. The suggestion was that when a jet ski jet is not in the water it produces no force. While I understand that this is indeed wrong (and furthermore is a liquid, not a gas), the acceleration of the water pumped in jet form out the back does cause some action reaction, it is I believe much less than the same jet pumped into a water medium.
My expectation is that the presence of gas behind the rocket (particularly at lift off when velocity of rocket is slow) may get compressed by the rapidly exiting gas plume and provide a slight (likely negligible) push. Not sure what happens when rocket gets up to speed.
But I would like a on answer on the jet ski question as well. Likely I am comparing apples to asparagus.
Thanks
https://www.rocketryforum.com/showt...y-Doesn-t-Work-in-the-Vacuum&highlight=Vacuum
And thought what the heck, maybe it will be fun . I know....I need to get out more.
Anyway, these guys take a certain amount of science and layman's thinking and try to contradict the science of Rocketry in general and NASA in particular.
In any case they raise some legitimate questions and for the most part are polite. In reviewing the posts I find a tremendous misunderstanding if what a vacuum is (and more importantly IS NOT!). Some of the concepts I think I may need a bit of help to answer. I will not claim to represent THE ROCKETRY FORUM, so if I make mistakes it will not reflect on our Forum. I do think some of these questions may also be educational for newbees (and some oldsters on our forum, hence posting here.)
question 1
While I do no doubt the fact at action/reaction is sufficient and certainly the dominant force in rocket propulsion, DOES the presence of air (mass) behind the rocket have any effect, positive or negative, in the degree of force generated (does is provide any additional "push"). One of the examples used in ClueForum was a jet ski. The suggestion was that when a jet ski jet is not in the water it produces no force. While I understand that this is indeed wrong (and furthermore is a liquid, not a gas), the acceleration of the water pumped in jet form out the back does cause some action reaction, it is I believe much less than the same jet pumped into a water medium.
My expectation is that the presence of gas behind the rocket (particularly at lift off when velocity of rocket is slow) may get compressed by the rapidly exiting gas plume and provide a slight (likely negligible) push. Not sure what happens when rocket gets up to speed.
But I would like a on answer on the jet ski question as well. Likely I am comparing apples to asparagus.
Thanks