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-   -   An embarrassing post (http://archives2.twoplustwo.com/showthread.php?t=406918)

Lestat 12-29-2005 02:52 AM

An embarrassing post
 
I hate to admit this, but for the longest time I though thrust was air pushing off of air. I thought a rocket blasted off by the massive thrust pushing the rocket away from the ground. As it climbed into the air I assumed air has some density so the rocket now had sufficient momentum to push off the air.

Of course I now realize this is all wrong. Thrust has nothing to do with "pushing" as in a water rocket. But I honestly still don't get it. I know that every action has an equal and opposite reaction, but I can't grasp what thrust uses for its opposing force if not the ground or air?

I've tried researching this on the web, but everything I've found is technically beyond me. Is there a thrust or aviation book for dummies? A physics for dummies would be a great book! I love this stuff, but it's beyond my grasp. Don't get me started on after-burners. It gets real ugly. It sucks to be uneducated.

12-29-2005 03:00 AM

Re: An embarrassing post
 
Conservation of momentum.

http://www.howstuffworks.com/rocket1.htm

uuDevil 12-29-2005 03:07 AM

Re: An embarrassing post
 
In a pressurized, closed container, air pushes on the inside surfaces of the container. If you put a hole in the side, air no longer pushes on the missing area (the hole), so there is an imbalance of forces. This pushes the container (rocket) in the direction opposite that of the hole (nozzle) out of which gas is escaping. The rocket pushes against itself!

Lestat 12-29-2005 03:10 AM

Re: An embarrassing post
 
Whoa! Thanks!!! That's exactly what I was looking for! It even stated that thrust is hard to grasp, so I don't feel quite as dumb. That's definitely a site that will go in my bookmarks. Thanks again!

daryn 12-29-2005 03:36 AM

Re: An embarrassing post
 
[ QUOTE ]
In a pressurized, closed container, air pushes on the inside surfaces of the container. If you put a hole in the side, air no longer pushes on the missing area (the hole), so there is an imbalance of forces. This pushes the container (rocket) in the direction opposite that of the hole (nozzle) out of which gas is escaping. The rocket pushes against itself!

[/ QUOTE ]

well, it pushes on the fuel

12-29-2005 03:54 AM

Re: An embarrassing post
 
http://www.sciencetoymaker.org/ballo...ges/newton.gif

uuDevil 12-29-2005 04:30 AM

Re: An embarrassing post
 
[ QUOTE ]
[ QUOTE ]
In a pressurized, closed container, air pushes on the inside surfaces of the container. If you put a hole in the side, air no longer pushes on the missing area (the hole), so there is an imbalance of forces. This pushes the container (rocket) in the direction opposite that of the hole (nozzle) out of which gas is escaping. The rocket pushes against itself!

[/ QUOTE ]

well, it pushes on the fuel

[/ QUOTE ]

Yeah, ok. It just seems more natural to me to consider the fuel to be part of the rocket. If we think of them as separate, then the fuel and the rocket push against each other.

BluffTHIS! 12-29-2005 01:00 PM

Re: An embarrassing post
 
Post this in OOT and you'll get some different definitions of thrust than given here so far.

Lestat 12-29-2005 01:48 PM

Re: An embarrassing post
 
LOL- That's one reason why I banned myself over there.

12-29-2005 09:22 PM

Re: An embarrassing post
 
In Wikepedia under "The New York Times" I found this famous mistake:

Famous mistakes
In 1920, a New York Times editorial ridiculed Robert Goddard and his claim that a rocket would work in space:

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


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