Suppose I stretch an ideal spring by distance $x$ then we know that the potential energy stored in the spring during elongation is $kx^2/2$. Now if I leave the spring it returns back to its natural length instantly and its Potential energy becomes 0. But if no body is attached to the spring where was this Potential energy transferred?
Newtonian Mechanics – How to Measure and Understand the Elastic Potential Energy of a Spring
energy-conservationfrictionnewtonian-mechanicspotential energyspring
Best Answer
The idealization of zero mass often presents a contradiction when one looks at the system energy, as the kinetic energy is always identically zero, rendering many work–energy analyses invalid and ineffective.
The idealized spring has no mass and extends and retracts instantly, among other unrealistic qualities. The real spring has mass, extends and retracts over finite time, and snaps back and bounces with internal friction when suddenly released, ultimately dissipating stored strain energy as heat.