Why do carrots curl when cut lengthwise?

May 15, 2011 2:46 PM

Why do carrots curl when cut lengthwise?

Take a carrot (store bought in my case), peel the skin, cut off top and bottom. Cut in half lengthwise. Whoa! The two halves instantly curl inward. Take the two halves and cut in half lengthwise. Major curl! But why?

posted by R. Mutt to Science & Nature (4 answers total)

Best answer: The stresses in a whole (or at least, whole-cross-section) carrot are balanced radially. The tendency of one half to curl inward is balanced by the other half trying to do the same. Once you cut it, the pieces no longer have that balance. If you notice, when you halve the halves, they curl toward the center, not to the original parting line.

Why? because the center of the carrot is, if you look closer, made of a different stuff. Look up xylem and phloem.
posted by notsnot at 2:57 PM on May 15, 2011 [4 favorites]

Interesting point, notsnot. Can someone clarify which way cut lumber bends (towards the heartwood, or away) as it dries?

I assume the instantaneous carrot bending, versus as-it-dries wood bending, is a function of how much more pliable carrots are than trees.
posted by IAmBroom at 4:00 PM on May 15, 2011

With lumber, it depends. What usually happens (for plainsawn wood) is that it cups away from the heart wood, but that's in response to it drying out and the less dense rings drying more quickly than the more dense rings. This is usually width-wise, not length-wise, though.

If you get a hold of something called reaction wood, which is from a tree growing at a funny angle, or having to support one huge branch on one side, it will do all sorts of odd things fresh off the saw, dried or no.

Obviously the stresses on carrots are going to be different than the stresses on trees, but the phenomenon is likely to be the same sort of thing - internal stresses due their growth environment being relieved when you cut them.
posted by Kid Charlemagne at 5:38 PM on May 15, 2011 [1 favorite]

Merely being made of different materials is not enough to explain why the stress would differ radially.

I don't know about carrots, but trees deliberately set up their trunks so that the exteriors are pre-stressed. There is an excellent diagram and discussion of this in Structures, or, Why Things Don't Fall Down I believe. It's similar to the way steel bars are set into concrete.

They aren't just put in there, they are put in such that they actually pull the concrete block in on itself, because concrete is good at compression but bad at tension. Then if there's an outward pull later (tension), the concrete is merely in less compression (good) rather than drifting over into actual tension (bad).
posted by DU at 4:52 AM on May 16, 2011