Talk:Gravity drag
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[edit] Example section
I hope I have not started an edit war by re-deleting the example. Personally I found it not only unnecessary (because the text of the article explains the concept quite well), but also confusing because its relation to the topic of gravity drag was never explained. --P3d0 03:36, Dec 6, 2004 (UTC)
- It says
- When applying delta-v against gravity to increase specific orbital energy, it is advantageous to spend the delta-v as early as possible, rather than spending some, being decelerated by gravity, then spending some more.
- This is demonstrated with the simple concrete example.--Patrick 09:55, Dec 15, 2004 (UTC)
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- Sorry chief, you're the victim of your own clear explanation. Looking at the example again, I just can't imagine someone not understanding the concept, then reading the example and saying "oh! NOW I get it!". --P3d0 21:42, Dec 15, 2004 (UTC)
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- More importantly, it claimed to be an example of gravity drag, yet the words "gravity drag" never appeared in the example, which makes it a poor example by inspection, but is also symptomatic of the example's lack of clarity and precision. A person who doesn't "get" gravity drag from your perfectly adequate explanation is going to need some serious hand-holding. Crafting a good example will take some work, but if you think it's important, we can give it a try. --P3d0 04:35, Dec 16, 2004 (UTC)
[edit] Relativity
Are we sure "gravity drag" is a real term from relativity? I think we need a better source for this than a single geocities page. Also, the relativistic effect is unrelated to the astrodynamical one (which is purely classical), so this article should be restructured to reflect this. --P3d0 21:40, Dec 15, 2004 (UTC)
- seems to me they're the same -- help me out if i don't understand it fully -- i'll clarify to show that it's not strictly relativistic ... just describes the phenomenon. [1] Ungtss 22:40, 15 Dec 2004 (UTC)
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- Firstly, why are you linking to a shadow of Wikipedia, when you could just go to Gravity? :-)
- Secondly, I think you're confusing 'gravity drag' with frame-dragging. the text on the link says that the term is the author's invention: "I call this effect gravity drag". He's not a reliable source. He's certainly wrong about the tidal locking of moons to their primaries, which was understood without any need for relativity. I think he's also wrong about Mercury, which is precessing but not losing energy. Double stars rotating fast enough to emit gravitational radiation could be said to be experiencing drag, but I don't recall anyone doing so. In sum, this section should be cut.
- —wwoods 00:53, 16 Dec 2004 (UTC)
- well alright then, i'll yield to the more educated mind -- cut away:). Ungtss 02:18, 16 Dec 2004 (UTC)
[edit] Bogosity?
"It might be expected that the gravity losses would up to 9.8 m/s per second of thrusting. However, by thrusting at an angle wherever possible, the overall losses are reduced by Pythagorus."
Um no. If you thrust at, say, 4g diagonally at the right angle so that you get 1g vertical component, do the maths and you get 3.87g horizontal component. So it's more efficient to thrust diagonally than to have two engines, one vertical and one horizontal. It really is due to pythagorus, and it really does reduce the gravity losses.
- Ok, I see what you mean. You're just reminding us that forces are a vector quantity. That's a good point that was missing from the article. I don't think an unexplained reference to Pythagoras is sufficient, though... I'll see if I can think of anything better. --P3d0 20:52, Jun 17, 2005 (UTC)
[edit] Centrifugal Force
A may be pedantic, but centrifugal force is ficticious. Second, the reason we want horizontal speed is never explained. I am guessing that it is due to the fact that at a sufficiently high velocity you enter a state of constant freefall, but this is just a guess.
- It's not really ficticious in a rotating frame of reference, such as an object rotating around the center of the Earth. Or if you think it is ficticious, many other everyday forces in physics are also ficticious.WolfKeeper 02:24, 15 July 2006 (UTC)
This article says: "horizontal speed... provides a centrifugal force". Speed providing force is a very poor thing to say without a large amount of explanation about the reference frame in use and real vs. ficticious forces. Also, it is stated as a given when it also depends upon the location of the object! There are better ways to describe this effect without adding to the confusion.
[edit] Invitation
Work is currently in progress on a page entitled Views of Creationists and mainstream scientists compared. Also currently being worked upon is Wikipedia: NPOV (Comparison of views in science) giving guidelines for this type of page. It is meant to be a set of guidelines for NPOV in this setting. People knowledgable in many areas of science and the philosophy of science are greatly needed here. And all are needed to ensure the guidelines correctly represent NPOV in this setting. :) Barnaby dawson 21:33, 27 Dec 2004 (UTC)
[edit] Vector Considerations
The comment about directing the thrust downwards to increase acceleration would presuppose either a really weak surface or that the rocket is already airborne. Since gravity drag seems to be concerned with getting up higher, this example seems silly and confusing (gravity generally tends to make it easy to accelerate downwards.) 128.151.161.49 Iain Marcuson
