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Jumping off a moving object

  1. Mar 27, 2009 #1
    i wondered what would happen if you took f.eks. your dirtbike on top of a moving train, drove against the rear end of the train (backwards), and made sure you had 0 velocity compared to the ground. if the train is moving north at 12m/s and you are moving south at 12m/s, will your dirtbike "stand still" when you jump/fall of the train?
  2. jcsd
  3. Mar 27, 2009 #2
    Exactly. You would fall straight down, just as if someone had simply dropped you from "train-height" (not recommended).
  4. Mar 27, 2009 #3
    thank you!
  5. Mar 27, 2009 #4


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    I'd stock up on the Preparation H first...
  6. Mar 27, 2009 #5
    An intrepid young student named Raleigh
    Deserted a fast moving traleigh
    To discover a flaw
    In Newton's first law
    but his efforts were faleigh, by galeigh.
  7. Mar 27, 2009 #6


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  8. Mar 27, 2009 #7
    Your wheels however would still be spinning at 12 m/s. You'd fall straight down but immediately lurch forward.
  9. Mar 29, 2009 #8


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    Was that a dig?!
  10. Mar 29, 2009 #9
    Not in the least. A lurch backwards, maybe.
  11. Mar 29, 2009 #10


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    Also, your front wheel would start falling first, because it would come off the train first, and so the bike would also rotate slowly, back-over-front. :smile:
  12. Mar 29, 2009 #11
    skeptic2 and tiny-tim are both right, of course.

    I was just talking about relative velocities.
  13. Mar 29, 2009 #12
    jumping off a FAST object

    Not if the rider leans back at that point. What would really be neat is if the train is going faster than the bike, so the jumper needs to do a 180 in midair and lands on the ground chasing the train :smile:
  14. Mar 31, 2009 #13


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    Interesting concept, that made me smile...

    If this is the inevitable future of Freestyle Motorcross stunts I'll be damn happy. They already have such great senses to things like rotation and velocity, it's actually quite beautiful to watch. It would be wildly pleasing to see such a vast inprovement in skill due to the knowledge and reliability of such physics because it's sports like these that I feel show the absolute peak of human ability. Certain things are only possible if you risk your life and it's amazing to see that these guys can do them.

    Please enjoy, for the physics. Calculation at it's best...

    Last edited by a moderator: Sep 25, 2014
  15. Mar 31, 2009 #14


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    You would not lurch. The wheels have too little momentum to cause any appreciable lurch.

    I think a cyclist would be quite hard-pressed to not automatically compensate for this.
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