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  1. #76
    I like SF. SF is cool. Steven L Jordan's Avatar
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    Quote Originally Posted by ian_sales View Post
    Except there's no such thing as centrifugal force. It's a convenient fiction...
    Centrifugal Force is a real phenomenon, based on demonstrated laws of mass and motion. It is not gravity, but it provides a force effectively comparable to it. Its effectiveness in space has been demonstrated by the Skylab astronauts.

  2. #77
    Registered User ian_sales's Avatar
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    Quote Originally Posted by Steven L Jordan View Post
    Centrifugal Force is a real phenomenon, based on demonstrated laws of mass and motion. It is not gravity, but it provides a force effectively comparable to it. Its effectiveness in space has been demonstrated by the Skylab astronauts.
    No, it' s a fictitious force. It either refers to the effects of inertia during angular motion or to centripetal force.

  3. #78
    Everyone see the article knocking #1 off the list of myths? Or rather, taking out of science fantasy and placing it firmly in the realm of hard SF.

    http://www.space.com/17628-warp-driv...aceflight.html

  4. #79
    SF Author SR_Seldon's Avatar
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    Ian, you are confusing the matter. While you are being very precise in you terminology, you are not being very practical in as far as this discussion is concerned. Centrifugal Force is a lay expression for the force felt when spinning an object, such as a centrifuge, bucket on a rope, or those fun amusement park rides. The proper scientific name is centripetal force and is as valid for creating the illusion of gravity as the vomit comet or the space shuttle are for creating the illusion of lack of gravity (both are technically freefall). For most practical purposes, especially in fictional storytelling, the illusion is as good as the real thing.

  5. #80
    SF Author SR_Seldon's Avatar
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    Quote Originally Posted by Overgeeked View Post
    Everyone see the article knocking #1 off the list of myths? Or rather, taking out of science fantasy and placing it firmly in the realm of hard SF.

    http://www.space.com/17628-warp-driv...aceflight.html
    Yes, quite fun. It is limiting in some ways, but it creates the very real possibility of an FTL robotic probe in the near future, possibly our lifetimes. New fodder for us SF writers to exploit.

  6. #81
    Quote Originally Posted by ian_sales View Post
    No, it' s a fictitious force. It either refers to the effects of inertia during angular motion or to centripetal force.
    Okay... it's the battle of the dictionaries.... OED (Oxford English Dictionary) has

    centrifugal = moving or tending to move away from the centre

    centripetal = moving or tending to move towards a centre

    So the artificial gravity induced by spinning a spacecraft is centrifugal force as the people are being pushed outward from the centre.

  7. #82
    I like SF. SF is cool. Steven L Jordan's Avatar
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    Quote Originally Posted by Overgeeked View Post
    Everyone see the article knocking #1 off the list of myths? Or rather, taking out of science fantasy and placing it firmly in the realm of hard SF.
    "Firmly in the realm of hard SF"? Not quite. No one's even proven that they can create a "warp bubble," much less sustain one, enlarge it, wrap it around a spaceship using "exotic matter" and shape it in order to squeeze the spacecraft through spacetime. I'd say #1 still qualifies as a myth.

  8. #83
    Registered User ian_sales's Avatar
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    Quote Originally Posted by Rosie Oliver View Post
    Okay... it's the battle of the dictionaries.... OED (Oxford English Dictionary) has

    centrifugal = moving or tending to move away from the centre

    centripetal = moving or tending to move towards a centre

    So the artificial gravity induced by spinning a spacecraft is centrifugal force as the people are being pushed outward from the centre.
    See http://en.wikipedia.org/wiki/Centrifugal_force and http://en.wikipedia.org/wiki/Centrif...eference_frame)

    (I should have put "reaction to centripetal force" earlier, which is reactive centrifugal force. But in the context of rotating something to generate gravity, centrifugal force is considered a fictitious force - see http://en.wikipedia.org/wiki/Artific...avity#Rotation)
    Last edited by ian_sales; September 19th, 2012 at 02:24 AM.

  9. #84
    Registered User ian_sales's Avatar
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    Quote Originally Posted by SR_Seldon View Post
    Ian, you are confusing the matter. While you are being very precise in you terminology, you are not being very practical in as far as this discussion is concerned. Centrifugal Force is a lay expression for the force felt when spinning an object, such as a centrifuge, bucket on a rope, or those fun amusement park rides. The proper scientific name is centripetal force and is as valid for creating the illusion of gravity as the vomit comet or the space shuttle are for creating the illusion of lack of gravity (both are technically freefall). For most practical purposes, especially in fictional storytelling, the illusion is as good as the real thing.
    Perhaps, but it seems silly to be scientifically inaccurate in a discussion on, er, scientific inaccuracies... :-)

  10. #85
    I like SF. SF is cool. Steven L Jordan's Avatar
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    Quote Originally Posted by ian_sales View Post
    See http://en.wikipedia.org/wiki/Centrifugal_force and http://en.wikipedia.org/wiki/Centrif...eference_frame)

    (I should have put "reaction to centripetal force" earlier, which is reactive centrifugal force. But in the context of rotating something to generate gravity, centrifugal force is considered a fictitious force - see http://en.wikipedia.org/wiki/Artific...avity#Rotation)
    The article seems to call centripetal force a "pseudo-force," because it is in reality an effect of the very real force of inertia upon rotational objects.

    Regardless, we know centripetal force can provide the effect of artificial gravity where there is none.

  11. #86
    Quote Originally Posted by ian_sales View Post
    See http://en.wikipedia.org/wiki/Centrifugal_force and http://en.wikipedia.org/wiki/Centrif...eference_frame)

    (I should have put "reaction to centripetal force" earlier, which is reactive centrifugal force. But in the context of rotating something to generate gravity, centrifugal force is considered a fictitious force - see http://en.wikipedia.org/wiki/Artific...avity#Rotation)
    It also depends which object on which the force is being applied - spacecraft or human... however I can't resist adding....

    May the force be with you!

  12. #87
    I like SF. SF is cool. Steven L Jordan's Avatar
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    From the list:

    4. Ships traveling at faster than light can communicate with other ships or planets.
    This makes me think of a corollary myth:

    Ships traveling at faster than light can use sensors to examine the space around them.

    If a ship was traveling FTL, no light or other particles should be able to interact with it, outside of those directly in front of it, without becoming severely dopplered... and the light or particles couldn't catch up from behind. Therefore, an FTL ship should be totally blind to anything happening behind it, and tunnel-blind to anything happening ahead of it. And, of course, by the time they detect anything ahead of it, it would be behind them before the signal even made it through the ship's electronics, much less through the human passenger's optic nerves.

  13. #88
    SF Author SR_Seldon's Avatar
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    Quote Originally Posted by Steven L Jordan View Post
    From the list:



    This makes me think of a corollary myth:

    Ships traveling at faster than light can use sensors to examine the space around them.

    If a ship was traveling FTL, no light or other particles should be able to interact with it, outside of those directly in front of it, without becoming severely dopplered... and the light or particles couldn't catch up from behind. Therefore, an FTL ship should be totally blind to anything happening behind it, and tunnel-blind to anything happening ahead of it. And, of course, by the time they detect anything ahead of it, it would be behind them before the signal even made it through the ship's electronics, much less through the human passenger's optic nerves.
    That's why I prefer to use hyperspace in my stories. A different dimension and a different set of rules. Unfortunately, from a science point of view, hyperspace is in pretty sketchy territory, even in theoretical physics. It just presents fewer complications when writing.

  14. #89
    I like SF. SF is cool. Steven L Jordan's Avatar
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    "Hyperspace" should have been given a prominent spot on the original list, given that we don't know whether it exists, whether we can access it, what rules apply to it, and how it will make FTL travel workable. Hyperspace is the ultimate Handwavium.

  15. #90
    SF Author SR_Seldon's Avatar
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    One of the confusions about hyperspace is how Asimov used the term. Herbert later had a more mystical process but a better label - folding space. That describes Asimov's concept better. Hyperspace has come to mean more of a different dimension such as in Star Wars or Babylon 5. I found the book Hyperspace, my Michio Kaku, to be enlightening about how highly theoretical it might be.

    In my fiction, I consider it a different but parallel dimensional space where all the high gravity objects in real space are echoed, but in a smaller scale. As I prefer the more theoretical end of physics, I have no problem pulling different theories into something that works, sometimes in dramatic ways, for my stories. But then, I consider what I have written, and most of what I plan to write in the future, to be space opera, so it fits what I write.

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