(I'm new to the Forum, so if I violate the rules unknowingly, please do let me know) So, during a recent research, I analyzed the frequency spectrum of our hand's oscillation while walking. As it turns out, it contains distinct harmonic frequencies (around 1.8*n Hz), and the second among them corresponds to the natural frequency of the first antisymmetric mode (FAM) of liquid oscillation inside an upright cylindrical container with radius 8cm and height 9cm. Would the following statement be physically sound? "Since the driving force (exerted by the hand, and subsequently the cup) contains a frequency component that corresponds to the natural frequency of the FAM, resonance occurs for the FAM." Or does resonance only occur when a purely sinusoidal signal is imposed upon the system? Thanks.