Explaining Physics on Instagram: "This video demonstrates the principle of sound resonance in an air column, often called a closed-end tube resonance. The man is blowing across the top of a test tube, creating a standing wave within the air column, which produces a sound at a specific frequency (the fundamental frequency or a harmonic). When he adds water to the test tube, the length of the air column above the water surface decreases. Since the wavelength \lambda of the sound wave that can reso