[celticjames]

There's a great sci-fi novel, The Windup Girl by Paolo Bacigalupi, set in a post-oil world where tightly wound springs are used to store energy, as we do now with clocks. One of the subplots deals with a character trying to develop a material that can be wound tighter and more compactly without breaking. Or explosively unwinding. I'm not an engineer or physicist, so I've wondered, what is the theoretical limit for storing energy in a spring. Sci-fi stories usually do a bit of handwaving with nano/bio/quantum-tech to make magic materials, but what is the real science? Cars and laptops powered by springs sounds plausible (and awesomely steam punk) to me.

[Anechoic]

what is the theoretical limit for storing energy in a spring.

I spring is a material (usually a metal, but could be a plastic as well) that is under stress, typically tension, torsion or compression (depending on type of spring). The limit is basically the yield strength of the material, which is the point where the stress vs strain curve goes nonlinear and the material begins to plastically deform. Obviously the fracture limit represents catastrophic failure of the material, but that is higher than the yield limit.

Basically, it's a material strength and elasticity problem.

[wisty]

Mechanical storage has safety issues when it's used for transport. Unlike gasoline (in real life, not movies) mechanical storage does tend to release all its energy at once in a crash.

[mikeash]

The Windup Girl was a good novel but its science was poor, at least when it came to energy. The posited system of generating energy by using large animals to wind up springs is completely ridiculous, even in the semi-post-apocalyptic, heavily bio-engineered future it's set in.

[Gravityloss]

spring suck in energy density, compared to batteries