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Plane of Reference

  1. Sep 18, 2015 #1
    I saw random question somewhere on the internet a couple of weeks ago and it got me really thinking about it.

    Supposedly you got a remote control miniature toy helicopter hovering inside a bullet train, if the bullet train suddenly started and accelerated to 200km/hr in 3.5 sec, will the toy helicopter hover with respect to the moving train or will it crash somewhere inside the train?
  2. jcsd
  3. Sep 18, 2015 #2


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    How many "g?" How many "g" can the toy handle?
  4. Sep 18, 2015 #3


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    When the train accelerates, the back wall of the compartment will push on the air in the compartment, very quickly bringing it up to speed. (That's why you don't feel any wind when you're sitting in a closed compartment in a moving train - you, the air, and the train are all moving at the same speed).

    The toy helicopter is supported by the air, so it's going to do whatever the air is doing. If the acceleration of the train is reasonably slow, the helicopter will just be carried along with the air as it keeps up with the train. If the acceleration of the train is high enough, more interesting things can happen, but that will depend on the specific numbers involved.

    You might try comparing this case with the behavior of a pencil resting on a table on the train. If the train accelerates or decelerates sharply enough the pencil will be thrown off the table, but if the acceleration is more gradual the pencil will stay put as it, the table, and the pencil all speed up. The helicopter is being accelerated by the force of the air on it and the air is accelerating because it's being pushed by the back wall of the compartment; the pencil is being accelerated by the force of friction between it and the table, and the table is being accelerated because it's fastened to the accelerating train.
  5. Sep 19, 2015 #4
    What would happen if it was in another vehicle with the windows open or something similar? perhaps a jeepney
  6. Sep 19, 2015 #5


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    What do you think and why?
  7. Sep 19, 2015 #6
    well in my opinion perhaps the back windows are open, the toy copter would hover in the same place leaving it outside while the jeepney moved forward since there is no contained in the jeepney that would move it with respect to the vehicle since it's an open type of vehicle
  8. Sep 19, 2015 #7


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    The helicopter would most likely crash against the back wall.
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