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Name: William M.
Status: Other
Age: Old
Location: N/A
Country: N/A
Date: November 2002


Question:
When a tall, brick, chimney falls through an arc (rather than collapsing) it always breaks apart near the middle after falling through an arc of about 45 degrees. Is this caused by differential gravitational forces applied along the length of the chimney due to the fact that the structure of the chimney, if it does not break, would force all of the chimney constituent components to strike the ground simultaneously even though the free-fall time from various heights along the chimney would result in separate components hitting the ground at different times?



Replies:
Yes. When a structure like a smokestack falls with a pivot point at ground level, its tip falls much faster than its base. However, the pull of gravity draws each part equally. The tip of the smokestack is pulled downward faster than by the action of gravity alone, and the base is held back. This results in tension along the leading edge of the structure. Masonry is not very strong under tension, so the structure breaks before the smokestack even hits the ground. The resulting pieces then can free fall to the ground.

Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois



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