Name: William M.
Date: November 2002
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
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
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
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