### Re: Breaking uncooked spaghetti by bending always results in 3 pieces. Why?

Date: Sun Mar 26 11:04:18 2000
Posted By: Sidney Chivers, , Nuclear Engineering, retired
Area of science: Engineering
ID: 953869775.Eg
Message:
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Spaghetti is brittle but also elastic.

It is possible to break spaghetti into only two pieces by shearing rather
than bending it.  Shearing in the sense that the two points at which the
spaghetti is held are as close together as possible and the force applied
is normal (at a right angle or 90 degrees) to the length of the spaghetti.

When you bend a piece of spaghetti, and do so slowly, you will notice the
spaghetti bends at first, rather than breaking immediately.  With a high-
speed camera you should also be able to observe that the curvature is
smooth right up to the instant of fracture.

Fracture occurs at the two points where the bending stress on the
spaghetti is greatest.  There is pressure but only a very small bending
stress in the two areas pressed between your fingers.  In the center piece
of spaghetti, the third piece after the spaghetti breaks, the spaghetti is
free to bend and spreads the bending stress.  Somewhere between the center
and each held end, is a point where the spaghetti is least capable of

Thanks for the question.  I had never considered spaghetti in quite that
manner.  I actually raced to the cubbard and snapped a few pieces.  If you
try shorter pieces, you will find the above does not work as well.  In
some instances you get two pieces but the break is to one side and in
others you get four pieces.  That is because the shorter the piece, the
less significant the curving of the spaghetti, as described above.

As a reference I used A Textbook of Materials Technology by Lawrence H.
Van Vlack, but it doesn't say a lot that is directly relevant to what I
have described above.  I also did not have a lot of luck finding a
spaghetti brittle-fracture reference on the web, but did find a
description of a balloon poping experiment.  Though the poping of a
balloon is much more complicated, spaghetti breaking and balloon poping
have a lot in common.
http://www.balloonhq.com/faq/howpop.html

sid
The following website describes a balloon poping experiment.

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