The surface of revolution of
y = 1/x
for x greater than 1, has finite volume but
infinite surface area!
Put another way, this object can hold a bucket of paint
(of volume Pi) but the same volume of paint is not enough
to paint that bucket!
How can this be?
Draw a picture. (It is fun to note that this object looks remarkably like a vuvuzela, made popular in the 2010 World Cup.)
Assign the calculations as a homework exercise in your calculus course.
Let students ponder the paradox until the next lecture.
The Math Behind the Fact:
The paradox is resolved by realizing that REAL paint cannot
be made infinitely thin. So when the trumpet is filled up
with paint, the paint only goes as far as the part of the
trumpet which is one molecule thick. But there is still
infinitely much surface area beyond that part of the
How to Cite this Page:
Su, Francis E., et al. "Gabriel's Trumpet."
Math Fun Facts.