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Dropping a cinder block

  1. Oct 22, 2015 #1
    I have been debating somebody and he says that if you drop one cinderblock from ANY height(onto 9 other ones) it will only destroy one cinderblock because it destroys itself in the process.I believe the higher up you drop, more blocks will be destroyed. Can someone tell which is correct and(most importantly) WHY??
     
  2. jcsd
  3. Oct 22, 2015 #2
    The faster the impact the greater amount of energy has to be dissipated on impact, so there will be a correspondingly greater amount of damage, primarily as a result of shock waves generated in the rigid and brittle blocks.
    If you drop from just 1cm the shock waves will be small so there will be very little if any damage to any block.
    As you increase the drop height damage will get more severe until the dropped block is destroyed every time, and you will begin to see increasing amount of damage occurring to the top block of the stack.
    Eventually the impact energy will become great enough that the top block of the stack is also destroyed every time.
    Increasing the impact energy still further would result in blocks further down in the stack taking damage too.
     
    Last edited: Oct 22, 2015
  4. Oct 23, 2015 #3
    Thank you so much for your reply!! I said the same thing, almost verbatim to this person. He said I was wrong because of newton's 3rd law. I told him that he misunderstands the law and there is more going on (1st and 2nd law, along with other physics). Can you possibly explain it in a more technical way( using equations and or modeling). Again THANK YOU!!
     
  5. Oct 23, 2015 #4
    To give a precise model of what would occur, so you could estimate for example the drop height at which the the first block breaks - that would require quite a lot of additional information about the exact composition of the blocks, their size, their density, elasticity (are they complete rigid or can they flex a small amount?), even their exact shape would be a factor, are the block surfaces completely smooth or not?, and probably more, it could quickly get very messy.

    The main point is that the collision generates shock waves in a rigid material, and rigid materials tend to shatter in these circumstances.
    Bigger shock waves at the point of impact will cause more damage at the impact site, and they also will travel further from the impact site with more potential to cause damage some distance away.

    If you really do need a detailed accurate predictive model for some reason there are people on this site who would be better qualified to have a go at that than me, but it would be a considerable task to do so.
     
    Last edited: Oct 23, 2015
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