# Violation of conservation of energy?

By squeezing a spring until it coils up, it then has more potential energy. So it will then have more mass, because mass is energy. So doesnt that violate the law of conservation of energy. The spring has more energy and mass after its squeezed than when it wasn't squeezed?

rcgldr
Homework Helper
It takes an external power source to increase the energy and mass of the spring.

Ameer Bux and John Pang
CWatters
Homework Helper
Gold Member
By squeezing a spring until it coils up, it then has more potential energy. So it will then have more mass, because mass is energy. So doesnt that violate the law of conservation of energy. The spring has more energy and mass after its squeezed than when it wasn't squeezed?

Conservation of energy only holds for a "closed system". That is a system that has no energy crossing the system boundary.

If your system boundary only contains a spring then no energy can get in or out so the spring cannot be compressed and COE holds true.

If your system boundary includes something (like a human) that can compress the spring then any energy gained by the spring is matched by an energy loss from the human - and once again COE holds true.

If you ever see an experiment that appears to violate COE it probably means you have forgotten to include something within your system boundary so it isn't closed (eg some energy is leaking into or out of your system).

Ameer Bux and lonelypancreas