Why does my guitar tune up by itself?
 

To people well versed in these fields, this might be the most idiotic question you've ever read, but it really doesn't make any sense to me. Whenever my guitar is out of tune after playing (both the acoustic and the electric), and I retune it, I always find that I need to tune the strings down to get them back in tune, rather than up. Logic, as far as my mind can grasp it, dictates that strings, after being plucked, picked and bended for long durations of time would loosen up, rather than tighten, but apparently that's not the case. It's a complete mystery to me, and if anyone could shed some light on this I would be thankful.

I can't tell you anything about the science, but I once left an acoustic guitar in its case for so long without touching it that when I went to play it the strings had tightened enough to pull the bridge off. Destroyed it.

Atmospheric conditions.
Humidity and temperature fluctuations will affect your guitar. Expansion, contraction, etc.

Yup. Thermal stresses and whatnot.

Just think, after you're done playing your guitar, it should be warmer than its surroundings (and hopefully in tune). Atmospheric air cools it, tautening the strings.

I've had strings snap inside my hardshell guitar case because I wasn't paying attention and left it in my trunk.

These people telling you it's atmospheric conditions are lying, it's really little guitar gnomes that sneak out of the walls when you aren't looking and tighten your strings.

The top should have bowed and cracks should have formed in the top long before any part of the bridge came off. The strings are actually anchored on a bridge plate UNDER the top, the piece on top is only partially structural, more for the sake of having a pretty, heardwearing piece of wood rather than spruce, in which to sit the bridge.

Any damage occuring because of those conditions would have to pull its way through the entire thickness of the bridge plate and guitar top in order to seperate the ebony/rosewood bridge plate.


Long story short, something else was very wrong with that guitar for simple neglect to cause something that severe.

Check your necks, I have a feeling they're bowing . . . does the electric have a whammy bar?

i have no idea

but once, I didn't play my 12-string for ages and the neck was severely bent - i took it to the repair shop and they said they can't do anything about it and i had to do the obligatory Pete Townshend

the tension of the strings makes it go out of tune-