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Rockets
Hi,
if there is no Atmosphere, where do rockets that go in Space get thrust from |
#2
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Rockets
In article ,
"George Kinley" wrote: if there is no Atmosphere, where do rockets that go in Space get thrust from They expell mass in one direction, which causes them to go in the other direction. The atmosphere has very little to do with how rockets work; it's just a simple law of physics: every action (force) causes an equal and opposite reaction (counterforce). The rocket "pushes" on the exhaust gas, causing it to accelerate to a very high velocity; the exhaust gas pushes back on the rocket, causing it to accelerate in the opposite direction (but more slowly, since the rocket has a lot more mass than the exhaust gas -- but that involves a different law). When you get into high school physics, you'll learn all about Newton's laws and how things like rockets work. It's really cool stuff, and it's neat to see you taking an interest in it already -- you'll probably be way ahead of most of the class! Best, - Joe ,------------------------------------------------------------------. | Joseph J. Strout Check out the Mac Web Directory: | | http://www.macwebdir.com | `------------------------------------------------------------------' |
#3
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On Thu, 10 Jul 2003, George Kinley wrote:
if there is no Atmosphere, where do rockets that go in Space get thrust from Stand on a skateboard on a smooth flat surface, with a bag of rocks. Throw the rocks in one direction, and you'll go in the other direction (except for the inconvenient effects of friction - use bigger rocks and you should see an effect). The rocket works exactly the same way. Throw mass away in one direction, and you go in the other direction. "Conservation of momentum" is what it's all about. -- Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/ Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html |
#4
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"George Kinley" writes:
if there is no Atmosphere, where do rockets that go in Space get thrust from From the Laws of Physics. Specifically, from Newton's Law of Action and Reaction --- See http://curious.astro.cornell.edu/question.php?number=100. A rocket throws mass out it's back --- that's the action. In order to conserve momentum, the rocket has to have an equal and opposite recoil --- that's the reaction. Rocket do not need an external atmosphere to "push against" --- the mass of their own exhaust is quite sufficient. -- Gordon D. Pusch perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;' |
#5
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In article Pine.LNX.4.50.0307110958020.29738-100000
@kolmogorov.physics.uq.edu.au, says... On Thu, 10 Jul 2003, George Kinley wrote: if there is no Atmosphere, where do rockets that go in Space get thrust from Stand on a skateboard on a smooth flat surface, with a bag of rocks. Throw the rocks in one direction, and you'll go in the other direction (except for the inconvenient effects of friction - use bigger rocks and you should see an effect). Or increase the speed. Stand on the skateboard and fire a shotgun, you'll move. Marc |
#6
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In article ,
George Kinley wrote: Hi, if there is no Atmosphere, where do rockets that go in Space get thrust from From the engine. Combustion creates pressure inside the engine, which pushes against all the walls, and against the front... except there's a big hole in the back, so nothing presses against the back. -- "Is that plutonium on your gums?" "Shut up and kiss me!" -- Marge and Homer Simpson |
#7
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Think about it this way. Suppose you have a tube closed at one end,
other end open, and you have a source of gas that has enough flow and pressure to maintain a fair pressure in the tube. Now, the force on the tube walls on the cylindrical part (the part without the end pieces) all cancel out because the force on every piece is cancelled out by the same force on the piece diametrically opposite. However, the pressure on the closed end creates a force that is NOT cancelled out by the open end. So the gas goes roaring out of the tube, but the force on the closed end 'pushes' the rocket forward. Now, real rockets have a 'nozzle' that makes better use of the gas flowing through it, pushing on walls of nozzle. So thrust of rocket comes from forces on nozzle, and on end of chamber opposite opening in nozzle. George Kinley wrote: Hi, if there is no Atmosphere, where do rockets that go in Space get thrust from -- Don Stauffer in Minnesota webpage- http://www.usfamily.net/web/stauffer |
#8
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Timo Nieminen wrote in message ...
On Thu, 10 Jul 2003, George Kinley wrote: if there is no Atmosphere, where do rockets that go in Space get thrust from Stand on a skateboard on a smooth flat surface, with a bag of rocks. Throw the rocks in one direction, and you'll go in the other direction (except for the inconvenient effects of friction - use bigger rocks and you should see an effect). The rocket works exactly the same way. Throw mass away in one direction, and you go in the other direction. "Conservation of momentum" is what it's all about. The direction of the rockets acceleration is irrespective of the direction of mass explusion. I could build a rocket that expels its mass upwards and it would still accelerate upwards. It is the explosion in the combustion chamber that pushes out in ALL directions. The upwards push makes contact with the top of the combustion chamber transferring a net upwards momentum to the rocket. However, the downward push from the explosion does not make contact with any structure from the rocket and escapes - so the net momentum is upwards. It should be noted that the actual upwards acceleration has nothing to do with the output direction of the expelled mass (I could very well route the mass from the explosion pushing downards via the top or side, although this is both extremely difficult and very inefficient). Also note that you don't even need mass to escape from a rocket. Inertial propulsion is not prohibited in physics if you think about it. All that needs to be done is to make the upwards push a greater impulse than the downwards push - the rocket would essential jerk its way upwards - after all there is no "conservation of displacement" with such an inertial system. |
#9
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if there is no Atmosphere, where do rockets
that go in Space get thrust from Others have already answered the question well, but I just wanted to say that this is a question that many people wondered about or misunderstood in the early days of rocket development. I think I've read quotes from some prominent people in those days who, to their embarassment later, declared publically that rockets wouldn't work in space. Of course many things about space travel can be a little hard to understand at first, since vacuums, weightlessness, etc. are things that we normally don't have to think about in our daily lives. Jim |
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George Kinley wrote:
Hi, if there is no Atmosphere, where do rockets that go in Space get thrust from Goddard was pestered with the same question. The answer is simple, by pushing against the propellent being thrown out through the engine. Consider a kid on a very low drag sled and a pile on beanbags. By throwing the beanbags in one direction, he can build up speed in the other direction. |
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