When an object vibrates at its natural frequency, what phenomenon amplifies the sound?

• A. Resonance.
• B. Reflection.
• C. Diffraction.
• D. Reverberation.

Answer: (A)

Resonance occurs when an object is driven at its natural frequency, allowing energy input to reinforce the vibrating motion. When the driving force matches the system’s natural frequency, the forces add in step with the oscillations, so each cycle builds on the last. This causes the amplitude to grow despite damping, producing a much louder sound. A good analogy is pushing a swing at just the right rhythm—the pushes align with the swing’s natural period, making it go higher.

Reflection, diffraction, and reverberation describe how sound waves move or persist, not the specific amplification that comes from matching a vibrating system’s natural frequency. Reflection is bouncing off surfaces, diffraction is bending around obstacles, and reverberation is the lingering sound from many surface reflections in a room.