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Easy conceptual mechanics question

  1. Sep 27, 2010 #1
    Just a random question i had in mind. should be very simple to answer. Assume I had a ball of some arbitrary mass (m), and dropped this ball from an arbitrary height (h). Now assume i had stretched out this mass to look something like a pole (lets just say a telephone pole). Now lets say this telephone pole fell (as you would imagine a tree falling) from the same height(h). would they both exert the same force once they hit the ground? what other relationships can i apply to these 2 objects? (acceleration, momentum, etc...?)
    An explanation with some concepts would be great..maybe F=ma or conservation of momentum can be applied? Anyways..thanks in advance
  2. jcsd
  3. Sep 28, 2010 #2
    The force an object exert when hitting the ground after falling is dependent on the amount of time it took the object to stop (or bounce back) and the velocity at the collision.
    [tex] F = \frac{\Delta p}{t} [/tex] where p is momentum and t is time.
    For example, when a pillow falls down and hit the floor it 'compresses' and this compression takes plenty of time so the force felt isn't that high. Take an object of similar mass to a pillow, say a basketball and the force exerted by it is much higher because the basketball bounces very fast compared to the pillow, thus the force is much greater.

    Answering your question, when you stretch your ball you are probably changing its physical properties and probably it will not bounce the same way and in the same time as the ball, but if you manage to make it stop once it reaches ground in the same time the ball stops once it reaches ground, then the force exerted will be equal.
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