How is a spring used to store energy?

Question

Physics Yuck!

Answer 1

potential energy
kinetic to wind it up
potential while its wound and bound
kinetic when released

Answer 2

The law of conservation of energy specifies a system (like a spring) has total energy TE = PE + KE + W; where PE is potential energy, KE is kinetic energy, and W is work.

For a relaxed spring TE = W; so its total energy is whatever it derives from work put into it. In this case, we have W = Fx; where F is the force applied to compress/stretch the spring x distance from a neutral position in a relaxed state.

As the spring is compressed/stretched, there is a bit of kinetic energy KE because the mass center is moving; so we have KE = 1/2 mv^2; where m is the mass at center of mass, and v is the velocity of the CM as it moves in relation to the compression/stretching. In most cases, KE is very small compared to TE; so we can ignore this energy in most cases. But what W becomes most is potential energy PE = kx.

Thus, when the spring is fully compressed/stretched, we have TE = PE + KE + W. We assumed KE = 0 and there is no work being done on a compressed/stretched spring so TE(compressed) = PE = kx = Fx = W = TE(compressing/stretching). This results because TE is the same no matter what is happening to the spring.

Therefore the spring stores a potential energy PE = kx that, upon returning to its relaxed state can do work W = Fx, with the change in x going in the opposite direction from when the potential was created. Through a series of gears and such, kx is turned into work which is then turned into KE that makes the hands on your wristwatch go around.

Answer 3

When a spring is compressed or stretched to a state other than its neutral length, it is storing energy as elastic potential energy. When the spring is released it will convert that potential energy into kinetic energy as it expands (from compression) or retracts (from being stretched).

This energy is stored as mechanical stresses within the spring.