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Huh. I recall my friends citing articles from popular publications where astronauts supposedly praised Gravity for its utter phycics realism. I disagree with yo

by Udo 13y ago

Huh. I recall my friends citing articles from popular publications where astronauts supposedly praised Gravity for its utter phycics realism. I disagree with you about Gravity (I didn't like it very much) but I agree that in the great scheme of things realism isn't that important for entertainment.

jessaustin 13y ago
SPOILER WARNING, I guess. I can't imagine an astronaut praising the "physics realism" of the "buffeted by the wind in space" moment that caused the death of the male character. His momentum had clearly been completely stopped by the tether, but instead of rebounding back toward the other tethered astronaut (as had happened multiple, more realistic, times earlier in the movie), some unknown force kept pulling him away until at last the tether came loose. If the setting were terrestrial the force would be inferred by most viewers to be the drag of a moving fluid such as wind. What similar force exists in space? I don't complain about the presence of unrealistic space plot device in unrealistic space movie, but there it is.
- GlennS 13y ago
  If I recall, the object they were tethered too was rotating. So it would be centrifugal force.
  - jessaustin 13y ago
    It's been some time since I've seen it, so you may be right. However, the situation you describe would only obtain once the entire system was rotating. As I recall, the female astronaut grabbed onto the object and the tether immediately stretched out tight, with no time to impart angular momentum to the tether or to the male astronaut. In that situation, I would expect the tether to wind around the object somewhat in the interim before the male came loose, and in that case he would have been imparted with some lateral momentum that would have taken him past the object (although not necessarily within retrieval distance) rather than straight away from it as I dimly recall from the film.
  - afterburner 13y ago
    It was not in any way portrayed as rotating. In fact Sandra's character seemed to be moving away from the ISS at a snail's pace. Furthermore, she was neither accelerating nor decelerating. It was poorly portrayed, that's why there is disagreement. As portrayed visually, it doesn't make sense. This was done I assume to stretch out the dramatic moment of decision so they could have an actual conversation about it. Even then that could have been achieved simply by having the conversation happen while the two were moving away from the ISS much faster. EDIT: Go to the movie with this exact shot to see what I mean: http://www.spaceanswers.com/wp-content/uploads/2013/11/Gravity-online-tether-death.jpg http://www.spaceanswers.com/wp-content/uploads/2013/11/Gravi... (from this article: http://www.spaceanswers.com/space-exploration/3802/16-things-gravity-got-wrong-and-some-things-it-got-right-too/ http://www.spaceanswers.com/space-exploration/3802/16-things... )
    - jessaustin 13y ago
      Hahaha looking at the picture I realize there is no way the "object", let alone the tether and astronaut, could be rotating fast enough to create such a force.
- Udo 13y ago
  > I don't complain about the presence of unrealistic space plot device in unrealistic space movie, but there it is. Normally neither do I, except if the movie's marketing made it an issue. I never actually researched realism claims about the movie (as I said, it came up during a discussion with friends, two of whom cited two different articles where astronauts had testified as to the accuracy of the movie's physics) until now. I have to say that claims of realism are in fact mostly confined to headline writers and journalists quoting astronauts out of context, for example when an astronaut referred to "stunning realism" of the special effects, that got mangled into "astronaut praises stunning realism of Gravity". Reading the actual reviews, I still believe that misleading claims were made, but apparently experts were mostly quoted creatively.
- bcoates 13y ago
  Bullock's leg was entangled with the parachute cords, and holding on to Clooney's tether with one hand. The Bullock-Clooney system was inertially travelling away from the ISS, to which one end of the parachute lines was anchored. The tangle of parachute cords was straightening as the distance increased. Eventually, they will run out of slack, at which point there will be an impact which (in Clooney's opinion) would either cause Bullock to lose her grip on the tether (dooming Clooney) or cause the cord looped around her foot to slip free (dooming them both). Bullock is barely connected to anything, has only one hand free (at best), and is in a terrible emotional state, rendering her incapable of useful action. Clooney throws off his tether which causes three things to happen: 1. A small amount of seperating momentum to both Clooney and Bullock, pushing Clooney further away and slowing Bullock towards the ISS. 2. Halving the force needed to stop Bullock's movement away from the ISS. 3. Freeing up Bullock's hands to improve her attachement to the parachute cord. I have no idea if the math works out but I don't see the theoretical problem with the situation physics-wise.
  - vilhelm_s 13y ago
    I think the parachute cord is already taut when this scene takes place (see 1:08 at http://www.youtube.com/watch?v=AjLcIxcSaik http://www.youtube.com/watch?v=AjLcIxcSaik), so I don't see how it can run out of slack beyond this. And in your version, where does the tension in the tether between Bullock and Clooney come from?
    - Retric 13y ago
      A realistic solution would be for them to be rotating which pulls the line taught and when released he would seemingly fall. However, I don't think that's shown in the actual visuals as they would have to be rotating fairly quickly or the cord needs to be really long for that to be a significant issue. Anyway, just looking at the previews I saw a enough holywood physics to give the thing a pass. The way the ISS was destroyed looked cool but the physics was terrible.
      - arrrg 13y ago
        Not really sure why you care about that. It doesn’t pretend to be accurate so it doesn’t really matter.
vinkelhake 13y ago
Aside from the thing that jessaustin mentioned, there's also the problem that Hubble and the ISS have completely different orbits and that you can't just take your back mounted whatever-it-is-called and fly between them.
- Udo 13y ago
  And that's exactly what I'm talking about, that was my point.

by Udo 13y ago

jessaustin 13y ago

SPOILER WARNING, I guess. I can't imagine an astronaut praising the "physics realism" of the "buffeted by the wind in space" moment that caused the death of the male character. His momentum had clearly been completely stopped by the tether, but instead of rebounding back toward the other tethered astronaut (as had happened multiple, more realistic, times earlier in the movie), some unknown force kept pulling him away until at last the tether came loose. If the setting were terrestrial the force would be inferred by most viewers to be the drag of a moving fluid such as wind. What similar force exists in space? I don't complain about the presence of unrealistic space plot device in unrealistic space movie, but there it is.

GlennS 13y ago
If I recall, the object they were tethered too was rotating. So it would be centrifugal force.
- jessaustin 13y ago
  It's been some time since I've seen it, so you may be right. However, the situation you describe would only obtain once the entire system was rotating. As I recall, the female astronaut grabbed onto the object and the tether immediately stretched out tight, with no time to impart angular momentum to the tether or to the male astronaut. In that situation, I would expect the tether to wind around the object somewhat in the interim before the male came loose, and in that case he would have been imparted with some lateral momentum that would have taken him past the object (although not necessarily within retrieval distance) rather than straight away from it as I dimly recall from the film.
- afterburner 13y ago
  It was not in any way portrayed as rotating. In fact Sandra's character seemed to be moving away from the ISS at a snail's pace. Furthermore, she was neither accelerating nor decelerating. It was poorly portrayed, that's why there is disagreement. As portrayed visually, it doesn't make sense. This was done I assume to stretch out the dramatic moment of decision so they could have an actual conversation about it. Even then that could have been achieved simply by having the conversation happen while the two were moving away from the ISS much faster. EDIT: Go to the movie with this exact shot to see what I mean: http://www.spaceanswers.com/wp-content/uploads/2013/11/Gravity-online-tether-death.jpg http://www.spaceanswers.com/wp-content/uploads/2013/11/Gravi... (from this article: http://www.spaceanswers.com/space-exploration/3802/16-things-gravity-got-wrong-and-some-things-it-got-right-too/ http://www.spaceanswers.com/space-exploration/3802/16-things... )
  - jessaustin 13y ago
    Hahaha looking at the picture I realize there is no way the "object", let alone the tether and astronaut, could be rotating fast enough to create such a force.
Udo 13y ago
> I don't complain about the presence of unrealistic space plot device in unrealistic space movie, but there it is. Normally neither do I, except if the movie's marketing made it an issue. I never actually researched realism claims about the movie (as I said, it came up during a discussion with friends, two of whom cited two different articles where astronauts had testified as to the accuracy of the movie's physics) until now. I have to say that claims of realism are in fact mostly confined to headline writers and journalists quoting astronauts out of context, for example when an astronaut referred to "stunning realism" of the special effects, that got mangled into "astronaut praises stunning realism of Gravity". Reading the actual reviews, I still believe that misleading claims were made, but apparently experts were mostly quoted creatively.
bcoates 13y ago
Bullock's leg was entangled with the parachute cords, and holding on to Clooney's tether with one hand. The Bullock-Clooney system was inertially travelling away from the ISS, to which one end of the parachute lines was anchored. The tangle of parachute cords was straightening as the distance increased. Eventually, they will run out of slack, at which point there will be an impact which (in Clooney's opinion) would either cause Bullock to lose her grip on the tether (dooming Clooney) or cause the cord looped around her foot to slip free (dooming them both). Bullock is barely connected to anything, has only one hand free (at best), and is in a terrible emotional state, rendering her incapable of useful action. Clooney throws off his tether which causes three things to happen: 1. A small amount of seperating momentum to both Clooney and Bullock, pushing Clooney further away and slowing Bullock towards the ISS. 2. Halving the force needed to stop Bullock's movement away from the ISS. 3. Freeing up Bullock's hands to improve her attachement to the parachute cord. I have no idea if the math works out but I don't see the theoretical problem with the situation physics-wise.
- vilhelm_s 13y ago
  I think the parachute cord is already taut when this scene takes place (see 1:08 at http://www.youtube.com/watch?v=AjLcIxcSaik http://www.youtube.com/watch?v=AjLcIxcSaik), so I don't see how it can run out of slack beyond this. And in your version, where does the tension in the tether between Bullock and Clooney come from?
  - Retric 13y ago
    A realistic solution would be for them to be rotating which pulls the line taught and when released he would seemingly fall. However, I don't think that's shown in the actual visuals as they would have to be rotating fairly quickly or the cord needs to be really long for that to be a significant issue. Anyway, just looking at the previews I saw a enough holywood physics to give the thing a pass. The way the ISS was destroyed looked cool but the physics was terrible.
    - arrrg 13y ago
      Not really sure why you care about that. It doesn’t pretend to be accurate so it doesn’t really matter.

vinkelhake 13y ago

Aside from the thing that jessaustin mentioned, there's also the problem that Hubble and the ISS have completely different orbits and that you can't just take your back mounted whatever-it-is-called and fly between them.

Udo 13y ago
And that's exactly what I'm talking about, that was my point.