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Why do wrecking balls amplify damage done?

  1. Dec 1, 2011 #1
    1. The problem statement, all variables and given/known data

    A wrecking ball is commonly used to destroy old buildings. The energy comes from a motor pulling a large pendulum back, which then allows it to swing against a wall. Why not just use the motor to do the same work on the wall?

    2. The attempt at a solution

    The kinetic energy AND the gravitational potential energy is used to break the wall with a pendulum whereas a motor will only have kinetic energy.
     
  2. jcsd
  3. Dec 1, 2011 #2
    For small buildings direct mechanical action is used, see,

    http://www.youtube.com/watch?v=I9FP7Y2Ig1Y&feature=related

    For large and stronger structures use the ball or explosives, see,

    http://www.youtube.com/watch?v=SJkdYuzViqo&feature=related

    Calculate the peak force generated when a 1 ton ball moving at 15 ft per second stops within 1 inch. If I did it right I get about 90,000 lbs. force concentrated over a relatively small area. It would be difficult to apply such a force many stories up with machines we have.
     
  4. Dec 1, 2011 #3
    I thought force is mass times acceleration - not mass times speed.

    edit: Never mind. I get it now. Thanks.
     
    Last edited: Dec 1, 2011
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