When an object is dropped onto a spring, it does not bounce back to its original height due to the non-ideal elasticity of the spring, which causes energy loss. This energy is transformed into other forms, primarily heat and sound energy, during the compression and subsequent release of the spring. The conversion of mechanical energy to thermal and acoustic energy accounts for the reduced height of the rebound. The discussion emphasizes the importance of understanding energy conservation in real-world applications, where perfect elasticity is unattainable. Overall, the energy lost in the process is a key factor in the behavior of springs.