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B Do Gravitational Slingshots cause G-forces

  1. Aug 19, 2016 #1
    Hi all,
    I am currently reading 'The Science of Interstellar' by Kip Thorne. Kip says that cooper could navigate around the Gagantua system using Gravitational Slingshots with Intermediate-Mass-Black-Holes. However these interactions would accelerate/decelerate the ranger by up to 22% of the speed of light, in (I assume) a fairly short time (The ranger's orbit is travelling at 33% of the speed of light and miller's planet at 55%). I know that that much acceleration over a short period of time generally means the inhabitants of the ranger will be subjected to very uncomfortable G-forces. However Einstein's general relativity states that Gravity is just an artifact of objects travelling in straight lines through curved space-time, which means no G-forces are experienced during free-fall. Would this property transfer over to Grav. slingshots which would mean no G-forces are experienced?
    Thanks in advance.
    Last edited: Aug 20, 2016
  2. jcsd
  3. Aug 20, 2016 #2


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    That's right. An accelerometer, which you could use to measure g-force, would register nothing from gravity except perhaps tidal effects.
  4. Aug 20, 2016 #3
    That's pretty cool, would you say I would need a good understanding of slingshot mechanics to understand why this is?

    If so, do you know any resources?
  5. Aug 20, 2016 #4


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    I'm pretty tired and about to go to bed, so I hope the following makes sense. There's two ways to think about this:

    1. Gravity is solely attractive, so it accelerates all objects at the same rate if they are at the same distance from the source. This means that when you slingshot around a massive object every part of you and your ship are being accelerated at roughly the same rate. Since the rate of acceleration is the same for both you and your ship, you will simply be floating there in free-fall along with your ship and will not experience any g-force.

    2. Gravity is actually the result of the curvature of spacetime and isn't an actual force. The reason you can slingshot around a massive object is because your path through spacetime is curved. Both you and your spaceship are taking roughly the same path through spacetime, so there's no relative motion between you and thus you aren't subjected to any forces from the walls of the spaceship pressing on you (g-force).
  6. Aug 20, 2016 #5
    Awesome, I guess that makes sense. Just might take a while to wrap my head around the concept for a layman like me.
  7. Aug 20, 2016 #6


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    I realise this thread is veering towards GR and its effects but there are classical arguments involved here, which are easier to understand. In common or garden Earth Satellite there is a well known phenomenon called Microgravity. The CM of the satellite is in free fall, whilst following its (let's say) circular orbit and it is Rigid. The contents of the satellite that are on the side facing towards the Earth are going 'too slow' to stay in their particular orbit and are being 'pulled up' by the walls of the craft. Likewise, items on the far side are going 'too fast' and are being pulled down by the walls off the craft. In Low Earth Orbit and with normal sized craft, these forces are very small but significant enough to be observed and experimented with. But in an extreme slingshot orbit at very high rates of speed and curvature, they could be much more significant. Different bits of a spacecraft would be subject to different accelerations and that could involve noticeable (or drastic) effects. It's along the lines of the spaghettification that is predicted when entering a black hole. I guess it would involve the Divergence of the g field.
  8. Aug 20, 2016 #7

    could this be shown on a graph or drowing out to get a better look at what would be happening???
    Last edited: Aug 20, 2016
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