Why is rolling up our sleeves, more stable than tucking them in?

Question

When sleeves are longer than your arms, two possible non-destructive ways of making them shorter are to roll them up or to tuck them in.

Rolled up sleeves [source: wikihow]

Tucked in sleeves [source: MS paint+ wikihow]

An experiment was performed to determine which of the two was more stable. Sleeves were rolled up identically in both fashions, and arms were jerked with roughly equal force until they had been unrolled completely. The number of jerks needed to unfold each configurations were measured, and experiment was repeated till arms were tired.

No. of jerks needed to unfold

Attempt	1	2	3	4	5
Tucked in	4	5	4	3	3
Rolled up	11	8	9	7	10

Result: Tucked-in sleeves only took 3.8 jerks on average. Rolled-up sleeves took 9 jerks on average, more than double that of tucked-in.

Conclusion: Rolling up sleeves are energetically more stable than tucking them under.

To demonstrate that this result is independent of the material, replicas of the sleeves were constructed using paper.

A. Folded outward

B. Folded inward

The effect became even more apparant with paper. B's fold was easy to undo, but A's was almost impossible to do without tearing.

What makes the fold in A much stronger than that of B?

Answer 1

It is caused by what the material needs to do to become unfolded. When rolling up, the material needs to be stretched in order to roll it down. When tucking in, the material can crumple a little to become untucked. The same rationale holds for the paper. Crumpling the edge is easier than stretching out the edge or crumpling in the bulk, therefore the rolled up sleeves are more stable.