English: Experiment using two tuning forks oscillating at the same frequency. One of the forks is being hit with a rubberised mallet. Although the second tuning fork hasn't been hit, it becomes visibly and audibly excited due to the oscillation caused by the periodic change in the pressure and density of the air originally caused by hitting the first fork, creating an acoustic resonance between the forks. However, if we attach a weight to one of the prongs of the second tuning fork, we see that the effect dampens, and the excitations become less pronounced as resonance isn't achieved as effectively. Performed by Prof. Oliver Zajkov at the Physics Institute at the Ss. Cyril and Methodius University of Skopje, Macedonia.