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Skateboard drops to flat.

  1. Jun 20, 2010 #1
    I've been having a bit of a discussion with a friend lately, about an object dropping off a horizontal surface, falling a certain amount, and then landing on another horizontal surface.

    The question is whether the impact of landing on the horizontal surface, will be affected by the velocity of the object.

    It started about flat-landing drops on a skateboard. Do you land as hard going fast as you do going slow? The size of drop would be between in the range of 4-10 feet.

    From my understanding, the velocity will make no difference, as an object is always affected by gravity in the same way, ie accelerating downward vertically at 9.8m/s. The horizontal velocity would not factor in, as when you land you would continue moving at the same velocity as take-off due to newtons law, thus there is no force dissipated here. Sorry, my ability to explain physics is quite limited!

    Could there be anything that I am not taking into account? I am assuming air resistance, would be negligible at these speeds. Is this correct?


    Any clarification and explanation of this matter would be highly welcomed.
     
  2. jcsd
  3. Jun 20, 2010 #2

    K^2

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    Everything is right, but there is one factor to which the speed makes a difference.

    When you leave the edge, the rear wheels are supported for a while after the front ones went over. If you aren't careful about placing your CM neatly over the rear wheels, you'll pick up a bit of a rotation going over. When you are moving faster, you spend less time in this half-suspended state, and so pick up less rotation, giving you better odds of safe landing.

    The vertical velocity with which you hit the ground, however, does not change. It is completely independent from horizontal motion.

    Air resistance would play a role if you were going fast enough, but that'd be something in the neighborhood of 100mph to make any sort of a noticeable difference. I'm pretty sure you'd have other problems if you tried to go that fast on the skateboard.
     
  4. Jun 20, 2010 #3
    Will this increase the amount of force that you land with though? It's not the odds of landing that I'm looking for (I'm assuming a perfect landing), just the amount of impact.
     
  5. Jun 20, 2010 #4

    K^2

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    If you land on the wheels in both cases, no difference. If you land on your face, it's going to depend on many things.
     
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