THE LAB
February 2006
The Italian Job Lab
The 2006 Winter Olympics are in Italy this winter; a
country of great history, great culture…and great food!
And, if I say “Italy”, what’s the first food that comes to
mind??? For me it’s SPAGHETTI!
When cooked up and served with a spicy arrabbiata sauce,
spaghetti comes alive to tease, tingle and tempt your taste buds!
But when they’re uncooked, these hard, rod-like objects are
pretty unimpressive.
However, to ignore the uncooked spaghetti strand is a crime
against engineering, structural mechanics and…well, interesting
science in general!
The Experiment:
Observe the fragmentation patterns of spaghetti.
Materials & Methods:
You will need:
• Your hands
• A minimum of 3 strands of uncooked spaghetti (although when I do this I
usually end up using about 20-30!!!)
• A pen (to record you observations)
• The Table of Results (see Page 2)
Here’s what you do:
• Take the ends of an uncooked strand of spaghetti in each hand
• Bend the spaghetti strand slowly by bringing your hands together until the
strand breaks
• RECORD YOUR OBSERVATION in the Table of Results (Trial A): e.g., how did
the spaghetti break; into how many pieces, etc…
• Repeat the procedure two more times and record observations each time
(Trials B & C) (CRAM Q: Why do we repeat an experiment 3 times?)
…fill your mind.
THE LAB
Results/Observations:
Trial
Observations
A
B
C
Table of Results
Page 2
…fill your mind.
THE LAB
Here’s what I got:
OK, I admit it; I did this procedure more than 3 times…just because it’s fun to
break pasta! Each time I did it the stick of spaghetti would bend, and then break
into 3-or-more pieces…NEVER into two equal sized ones.
The Explanation:
What we are looking at is FRAMGENTATION (i.e., how objects shatter). Although
this may seem trivial (breaking spaghetti…yippee!), researchers in France recently
published a bona fide scientific research article about this exact phenomenon
(Audoly & Neukirch, 2005).
The paper is very complex, and has many equations in it, so let’s break down the
main ideas: starting with the term elastic limit. This is a property that all solid
materials have, and refers to the point when an object can no longer return to its
original form in response to an applied load/stress/force. In simple terms: when
the applied stress is greater than the material’s elastic limit, permanent atomic
and/or molecular structure changes occur.
According to the French publication, a strand of uncooked spaghetti is a “thin brittle
rod”, which means that when the applied stress (i.e., bending the strand) is greater
than the spaghetti’s elastic limit, the strand will break (…talk about permanent
alteration of molecular structure!).
When the strand of spaghetti is bent it will ultimately reach its limit of curvature,
which causes the first break point. This initial break causes a “burst of flexural
waves [through] the newly formed fragments”.
Huh?
Page 3
…fill your mind.
THE LAB
Look at it this way:
1. The initial break causes two fragments:
INITIAL
BREAK
2. The process of fragmentation causes waves of vibration in the two fragments:
Wave of Vibration
Wave of Vibration
3. Each fragment is now considered an independent “thin brittle rod”. The resulting
waves of vibration cause additional curvature (i.e., bending) in the two
fragments, due to the oscillations of the waves. This bending is not as obviously
visible as when you bent the whole spaghetti strand, but nevertheless, it is there.
4. If the new bending, which result from the waves of vibration, causes a fragment
to go past its limit of curvature the fragment will break again, and the process
will repeat.
SECOND
BREAK
Page 4
…fill your mind.
THE LAB
The Implications:
Although we’re working with spaghetti, structural engineers can also apply the
principles learned from these experiments. This new insight on fragmentation can
influence the way metal rods are used to hold up buildings, the way bridges are
built and even the measures taken to prevent broken bones…Thank goodness for
spaghetti!
-by Mira Ray, PhD
References:
Hallett, McFarland, Stinson, Hunt, Renninger, Sullivan. 2003. Physics for the
Biological Sciences, 4th Edition. Canada: Thompson & Nelson.
Audoly B and Neukirch S. 2005. Fragmentation of rods by cascading cracks: Why
spaghetti does not break in half. Physical Review Letters 95: 095505.
Piquepaille R. 2005. “Why spaghetti does not break in half”:
http://blogs.zdnet.com/emergingtech/?p=17
Weiss P. 2005. That's the Way the Spaghetti Crumbles: Physicists solve a vexing
kitchen puzzle. Science News 168(20):315
http://www.sciencenews.org/articles/20051112/bob10.asp
Page 5
…fill your mind.