Physics of nail pullout 1

[crossframe]

I'm curious as to the mechanics that causes nails to back out of wood. I understand that normal moisture and drying cycles can cause nails to back out of the holes, but I'm talking about nails that end up an inch or more out of the wood - far beyond the "swollen" size of wet wood - and can easily be removed by hand. Is it lateral squeezing on the small tapered nail-tip? Vibration?

 

[PSlem]

It's ratcheting. Each time the wood swells it pushes the nail out a little, then it shrinks, grabs it again and pushes with the next swell.

Engineering is the art of not constructing...of doing that well with one dollar what any bungler can do well with two after a fashion.

 

[crossframe]

Seems to makes sense. Thanks.