#1
|
|||
|
|||
Rockets
Hi,
if there is no Atmosphere, where do rockets that go in Space get thrust from |
#2
|
|||
|
|||
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
|
|||
|
|||
Rockets
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
|
|||
|
|||
Rockets
"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
|
|||
|
|||
Rockets
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
|
|||
|
|||
Rockets
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
|
|||
|
|||
Rockets
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. |
#8
|
|||
|
|||
Rockets
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. |
#9
|
|||
|
|||
Rockets
In sci.space.tech John Schoenfeld wrote:
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 Err, no it's not. 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 In some ways, this is a not utterly inaccurate description of the rocket combustion chamber, up to the throat. However, at the throat the rules change. The gas enters the widening nozzle, and rapidly expands. The expanding gas causes a pressure against the nozzle walls, and the component of the force which acts opposite to the direction of the exhaust is transferred through the nozzle walls. If you just have a hole in the combustion chamber, the exhaust pretty much spreads over a hemisphere, and you get relatively little thrust. A deLaval (sp?) nozzle, produces a much higher thrust, as the exhaust is not a hemispherical expanding gas, but a relatively cold jet going in the opposite direction. 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). This is totally incorrect. A few seconds with a balloon, a bit of tape to tape the neck down to the balloon should convince you of this. 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. This is also totally incorrect. Conservation of momentum means that you have to expel something. -- http://inquisitor.i.am/ | | Ian Stirling. ---------------------------+-------------------------+-------------------------- "The theory of everything falls out trivially." -- Etherman, sci.physics kook. |
#10
|
|||
|
|||
Rockets
"John Schoenfeld" wrote in message om... 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. Umm. No. It's directly related to the direction of the mass expulsion. I could build a rocket that expels its mass upwards and it would still accelerate upwards. Good luck. 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). Nope, because as soon as you did that, your piping would have be acting just like the top of the combustion chamber. 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. Yes, you do need mass to escape. You can't design a rocket that pushes UP more than down unless it can eject mass out the back. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Titan 4s costly | AllanStern | Space Shuttle | 9 | February 17th 04 05:02 AM |
Von Braun rockets on Encyclopedia Astronautica | Pat Flannery | Space Science Misc | 41 | November 11th 03 08:10 AM |
The Non-Innovator's Dilemma | Rand Simberg | Space Science Misc | 76 | September 27th 03 03:09 AM |
The Life and Death of Russia's Space Shuttle Program , from Pravda | Locz | Space Shuttle | 0 | September 4th 03 02:49 PM |
"Why I won't invest in rockets for space tourism ... yet" | RAILROAD SPIKE | Space Station | 0 | July 30th 03 12:06 AM |