Re: Breaking sticks or spaghetti

[Leigh Palmer <palmer@sfu.ca>]

> I have a question that I can't quite get a handle on the physics of, perhaps
> bedause it involves some properties of materials that I am not aware of.
>
> When one takes a light stick or a piece of uncooked spaghetti and holds it
> near
> the ends and flexes it it sometimes does not break into two pieces but into
> three.  You end up with one piece in each hand and a short middle section
> which flies off as a projectile.
>  Why?
>    It would seem to me that a single break could be explained by considering
> two forces or torques in opposite direction causing bonds to break, but
> why would it happen two different places?  Unless they are somehow
> constrained to be
> simultaneous it seems that the first break would relieve any stress on the
> remaining free end so it should not break a piece off.
>     Any clues would be appreciated.

There are two influences here to consider, flexion and tension/
compression. Perhaps the problem should be controlled better to
see if there really are two different outcomes for the "same"
bending method. Try bending full, equal lengths of spaghetti by
holding them with only one finger at each end. Do you still get
both failure modes? the ratio of compression to flexion should
be the same every time this way.

Leigh