Emergent high-rise and long-span structures require vibration mitigators that adapt as decisively as the loads that excite them. This paper presents and validates a pendulum Tuned-Mass Damper (TMD) whose effective inertia is re-shaped in real time by varying the pendulum length. This solution enables adaptive vibration control in structures subjected to variable dynamic loads, such as wind or seismic activity, as well as changes in stiffness caused by exploitation. An experimental setup was designed and constructed, featuring a physical model of a high-rise building and a pendulum-based TMD with adjustable suspension length. System motion was recorded using an accelerometer. Vibration amplitudes were measured at resonance, both with and without the active damper engaged. A series of simulations was also done. The results confirm that the use of a variable-length pendulum significantly enhances damping efficiency compared to traditional fixed-parameter TMDs. The proposed approach demonstrates strong potential for implementation in modern high-rise structures and other engineering applications that require active vibration control. It is worth summarising that advances in structural dynamics increasingly demand intelligent vibration-control devices that can "think on the fly" and "adapt in real-time".