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Author Topic:   Quick Questions, Short Answers - No Debate
crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 66 of 341 (615790)
05-16-2011 7:47 PM
Reply to: Message 57 by Percy
05-16-2011 10:24 AM


Re: Propulsion in the vacuum of space
The controlled explosion of fuel in the combustion chamber causes gas to push outward in all directions. In the forward direction it encounters the wall of the combustion chamber, and it pushes against this wall, which being part of the rocket ship imparts a forward force to the whole vehicle. The forces of all the gas that pushes against the sides of the combustion chamber cancels out. There is no force from the gas that exits to the rear because the rear of the combustion chamber is open. The net of all this is a forward force.
No, this isn't right at all.
Space propulsion has nothing to do with gases being pushed off of anything, or pushing on anything. As Dwise says, it's all about conservation of linear momentum.
On an object in space with no external forces acting on it, linear momentum is conserved. That means it has to be the same both before you fire your engine and afterwards. So, if your engine is shooting hot gas particles out that way at a certain velocity, then your space ship has to gain a velocity in the opposite direction, such that the momentum of the gas particles (their mass times their velocity) is canceled out by the momentum of your spaceship.
It's conservation of momentum. It doesn't have anything to do with pushing. If you were to find the center of mass of all of the particles of gas you expended plus your spaceship after you fired your engine, you would find that it was exactly identical to the center of gravity of your spaceship plus its fuel before you fired your engine. Generally we're not concerned about this because the point of space travel is to move spaceships and their occupants to a specific place. We don't care about what happens to the fuel exhaust products once they've been accelerated away from the ship, so the fact that the total center of gravity isn't actually moving is just a bit of trivia.
Rocket engines have a bell-shaped nozzle not because that's necessary to be "pushed" against, but to keep the gases from expanding too quickly. There has to be some pressure in the engine nozzle to ensure combustion of the gases.
Edited by crashfrog, : No reason given.

This message is a reply to:
 Message 57 by Percy, posted 05-16-2011 10:24 AM Percy has replied

Replies to this message:
 Message 67 by Percy, posted 05-16-2011 8:47 PM crashfrog has replied
 Message 68 by slevesque, posted 05-16-2011 8:57 PM crashfrog has not replied
 Message 79 by cavediver, posted 05-18-2011 3:38 PM crashfrog has replied

crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 75 of 341 (615833)
05-17-2011 10:39 AM
Reply to: Message 67 by Percy
05-16-2011 8:47 PM


Re: Propulsion in the vacuum of space
Yes it is.
How, for instance, would your model be different than this?

This message is a reply to:
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Replies to this message:
 Message 76 by Percy, posted 05-17-2011 1:11 PM crashfrog has replied
 Message 78 by dwise1, posted 05-17-2011 9:28 PM crashfrog has not replied
 Message 85 by fearandloathing, posted 05-19-2011 9:23 AM crashfrog has not replied

crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 77 of 341 (615842)
05-17-2011 1:12 PM
Reply to: Message 76 by Percy
05-17-2011 1:11 PM


Re: Propulsion in the vacuum of space
I spent about two minutes trying to figure out how that was analogous to space travel before I realized you were burning me.
It's a slow brain day.

This message is a reply to:
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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 80 of 341 (616023)
05-18-2011 11:01 PM
Reply to: Message 79 by cavediver
05-18-2011 3:38 PM


Re: Propulsion in the vacuum of space
If I designed a rocket engine that had no combustion chamber at all - let's say a pair of hollow tubes delivered propellant and oxidizer to a location well aft of the rocket where it was ignited - would it be able to move? Or would it move simply as a function of the fuel and oxidizer it was spraying out, with the energy of combustion lost?
Thanks for the correction, though. I was hoping you'd arrive to explain how wrong I was.

This message is a reply to:
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Replies to this message:
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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 83 of 341 (616067)
05-19-2011 9:15 AM
Reply to: Message 82 by cavediver
05-19-2011 4:57 AM


Re: Propulsion in the vacuum of space
Think of the Orion spacecraft design, which ejects H-bombs out the rear, detonates them, and rides the shock-wave.
I think that was my favorite part of Larry Niven and Jerry Pournelle's "Footfall."
But now that I think of it - since you asked - why is there a shock-wave at all in the vacuum of space? It's easy to imagine a longitudinal wave through an atmospheric medium or the hot gases of chemical combustion, but how does the mechanical energy from the nuclear detonation actually reach the blast plate of an Orion-type spacecraft?

This message is a reply to:
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Replies to this message:
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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 102 of 341 (633170)
09-12-2011 9:46 PM
Reply to: Message 101 by nwr
09-12-2011 8:26 PM


Re: Computer Help?
I've noticed, especially on Vista/Win 7 platforms, a lot of network-related weirdness caused by the IPv6 drivers (Toredo IP Tunneling, etc), up to and including random BSOD's. I'm recommending that everybody experiencing persistent internet weirdness uninstall their IPv6 drivers (which is a bit of a complicated process, since you have to both uninstall the drivers and disable IPv6 support with a registry key, otherwise they just reinstall at next bootup.)
These drivers are just abominable and they solve a "problem" that nobody has, yet.

This message is a reply to:
 Message 101 by nwr, posted 09-12-2011 8:26 PM nwr has replied

Replies to this message:
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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 125 of 341 (633523)
09-14-2011 2:10 PM
Reply to: Message 120 by Taz
09-13-2011 11:09 PM


The Gnu Image Manipulation Program - the GIMP - has both batch processing (via "Script-Fu") and what you want to do, which is called "changing the color space."
http://www.gimp.org/
There's probably a script out there for doing this already. Apparently you can do it from GIMP's console:
http://www.gimp.org/tutorials/Basic_Batch/
Working with command lines may not be something you're very familiar with. But the GIMP is definitely free, does about as much stuff as most people know how to make Photoshop do, and is super-useful. I've used it for years.

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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


(1)
Message 128 of 341 (633566)
09-14-2011 6:16 PM
Reply to: Message 126 by RAZD
09-14-2011 5:01 PM


Re: Flat Earth / curvature test
If you set two plumb bobs a substantial distance apart - say, opposite ends of a very long bridge - and then use a telescope from a vantage point where you can see both, you'll see that they aren't parallel.
It's a convenient experiment for those of us who are landlocked.

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 Message 126 by RAZD, posted 09-14-2011 5:01 PM RAZD has replied

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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 131 of 341 (633656)
09-15-2011 10:51 AM
Reply to: Message 129 by RAZD
09-14-2011 11:11 PM


Re: Flat Earth / curvature test -- laser light shows
Have you calculated how far apart they would need to be to measure the difference?
Not all that far, I think. I couldn't find any information on it but I'm pretty sure a guy did this on a bridge in England a hundred years ago. I could be remembering wrong, of course.

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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 132 of 341 (633657)
09-15-2011 10:52 AM
Reply to: Message 130 by Dr Adequate
09-15-2011 4:59 AM


Re: Flat Earth
Oh, maybe that's the experiment I was thinking of. Thanks, Dr. A!

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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 144 of 341 (647904)
01-11-2012 6:44 PM
Reply to: Message 143 by foreveryoung
01-11-2012 6:11 PM


Re: chemistry question
If you protonate sulfuric acid (and you'd have to use a hell of a strong acid to get it to accept a proton) you get trihydroxyoxosulfonium, a cationic species.
Technically sulfuric acid is amphoteric but in practice I've never heard of it used as a base. Strong acids are weak, weak bases. I suspect the dissociation constant of that third proton is too high to be accurately characterized (but I could be full of shit.)

This message is a reply to:
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Replies to this message:
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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 146 of 341 (647952)
01-12-2012 8:10 AM
Reply to: Message 145 by foreveryoung
01-11-2012 6:51 PM


Re: chemistry question
This is the best answer yet.
It may be the worst answer yet, since you asked a question about hydrogen sulfide and I told you all about sulfuric acid. Sorry. But the answer is mostly the same: With a strong enough acid you can make hydrogen sulfide act as a base and form hydrogen sulfonium; it's an analogous compound to the hydronium that water forms when it acts as a base. It's a lot less stable than hydronium, apparently. Sulfoniums are more easily formed with larger, electron-donating substituents that stabilize the sulfur's positive charge. (I think. To tell the truth, I'm shit at organic chemistry.)

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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 159 of 341 (648341)
01-14-2012 6:12 PM
Reply to: Message 156 by Straggler
01-14-2012 5:08 PM


Re: Question About Pi
Can it be proved that Pi is irrational? How does one go about proving that a ratio such as Pi is definitely irrational?
http://en.wikipedia.org/wiki/Proof_that_%CF%80_is_irrational
How's your calculus?

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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 162 of 341 (648422)
01-15-2012 5:01 PM
Reply to: Message 161 by Butterflytyrant
01-15-2012 4:59 PM


Re: the flood
In your opinion, what would be the top 3 to 5 arguments to put on the table to support the position that the flood of Noah is impossible?
The existence of civilizations with continuous records all the way back to well before the flood supposedly happened, and they somehow never noticed?

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 Message 161 by Butterflytyrant, posted 01-15-2012 4:59 PM Butterflytyrant has replied

Replies to this message:
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crashfrog
Member (Idle past 1489 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 175 of 341 (648599)
01-16-2012 7:46 PM
Reply to: Message 174 by Buzsaw
01-16-2012 6:50 PM


Re: Explanation Of Global Flood
It is unknown what effected the climate change which caused the condensing of the atmosphere significantly enough to suddenly flood the earth.
Buz, it's "unknown" because it didn't happen. There was never any global flood and you've never at any time been able to substantiate that there was.

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