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Thread: Physics Flaw?

  1. #1
    Member Since
    May 2019

    Default Physics Flaw?

    I am currently rereading the books (highly recommended to any who haven’t) and I have come across what I think is an issue with how thrust gravity is portrayed in the series. Basically we have gravity is created by a ship moving very fast in a direction, which due to Newton’s laws, causes the contents of the ship to go in the opposite direction of thrust. What is portrayed in both the books and the show, is that as soon as ships cut thrust, this gravity is lost. Why should gravity stop when acceleration is cut? As there is no air resistance to slow, the ship is still moving at the same speed, so why does the force creating gravity stop? I would assume that in order for weightlessness to resume again, the ship would have to break. There are multiple mentions in the book (the one scene I can think of in the show is when thrust is cut on the Donnager right after the death of Shed) when the artificial gravity ceases immediately after acceleration stops, before a flip and burn. I have been trying to figure this out for a while, but I have no idea- just hoping that someone can explain it to me.
    Thank you!

  2. #2
    Member Since
    Dec 2014
    The People's Republic of New York

    Default Re: Physics Flaw?

    This make perfect sense. In a car, you are pressed against the seat if accellerating, and into the steering wheel or seat belt if braking. Same principle applies.

  3. #3
    John Diggle DigiFluid's Avatar
    Member Since
    Sep 2004

    Default Re: Physics Flaw?

    Essentially, it's small-scale relativity. What looks like the ship in motion to us, the outside observer standing on the surface of Earth/Mars/Ceres/wherever, is not the case for the people who are actually inside it.

    When the ship's thrust is going, the ship is 'in motion' relative to the people inside, and the motion differential of the ship's acceleration vs. the people inside is what's forcing them down into their crash couches. When they turn the ship's engines off, it is no longer accelerating relative to the people inside, and so it's no longer 'moving' at a different rate to the people inside, and so they float free.

    When you're in a plane, and it's rolling down the runway at 50 km/h, you feel like you're just sitting in a chair, right? But when the pilot cranks the engines up to full to get the plane off the ground, you're pressed back into your seat because even though you're already moving at 50 km/h, suddenly the plane you're sitting in is moving at 100 km/h--you feel the motion differential. Same principle.
    "A society grows great when old men plant trees, the shade of which they know they will never sit in. Good people do things for other people. That's it, the end." -- Penelope Wilton in Ricky Gervais's After Life

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