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Terminal velocity & Zero G.

  1. Jun 16, 2009 #1
    Hello everyone,

    I'm in great need of an expert answer and havn't been able to find much help at all, so I am hoping I have come to the best place.

    I have two questions regarding forces acting apon passengers in an aircraft.

    I would like to know how passengers would experience a zero gravitational force inside a pressurized aircraft, which would be in a fixed pitch 90 degee descent. Does this have anything to do with terminal velocity? Can it be achieved at all? I'm ignoring the structual limits of aircraft, and I don't want this to be a factor.

    Which leads me on the my second question, can the passengers inside a pressurized aircraft be accelerated beyond their own terminal velocity?

    I'm sorry if sound stupid in asking these questions, but I really would like a clear explanation.

    Many thanks in advance,

    Sam Crawford.
  2. jcsd
  3. Jun 16, 2009 #2
    To answer the first question:
    In order to achieve a net zero force on an object, all forces must either be zero or cancel each other out. If the plane were to do a climb (let's say about 45 degrees) before taking its dive, the passengers would feel weightless as the plane began to reach its maximum height (the plane would have to have slow down its turbines and begin pointing down gradually). What will happen then is that the forces of the plane on the passengers will zero out. Even though there still is the gravity from the Earth, the passengers will float around in the plane (because the plane and the passengers will be falling at the same speed) (the passengers' point of reference would be the plane). In order to experience a zero force at a 90 degree dive, the plane's turbines would have to be off instead of slowed down during the climb. The plane can only accelerate due to gravity. This doesn't have to do much with the terminal velocity of the plane (assuming that the aerodynamics and large mass allow this assumption to be true).
    To answer the second question:
    Since the airplane is accelerating downwards due to gravity, it is then accelerating everything inside of it. Think of driving in a car with the windows down, as you accelerate you don't feel a sudden rush of air. This is because the car is accelerating all of its contents, even the air. So, the passengers would be able to go faster in a falling plane than in free fall themselves.
  4. Jun 17, 2009 #3


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    Not sure if I'm understanding your question correctly, but here's an attempt.

    A "zero gravitational field" would feel just like the one you feel when you are in the ISS, for example. Technically, you are not in "zero gravity", you are simply free-falling towards the earth. Since everything around you falls equally fast, it seems like there is no gravity at all. Of course, the difference is that the ISS will keep falling around the earth while the passengers in a plane will eventually hit the ground. However, planes are used, for example to train astronauts. An aircraft there flies along a parabolic trajectory, the downward part of which corresponds to an acceleration of 9,8.. m/s/s towards the earth - effectively a free fall.

    Assuming that you mean by "terminal velocity" the velocity one would eventually obtain (due to the effects of friction), it is of course possible to accelerate beyond that. All you need is to add an extra acceleration to counter the friction. For example, free-fall until you reach the terminal velocity, then switch on a rocket booster which is pointed upward, so you get accelerated downward. However, I strongly suggest not trying that at home :P
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