Question

nancy applies a force to a violin string by pulling her bow across it. the vibrations of the string produce sound waves, which cause the wooden portion of the violin to vibrate at its natural frequency. the violin is designed so that a string vibrates at a frequency that matches the natural frequency of the wooden portion of the instrument. so repeatedly pulling the bow across this string allows to occur.

Explanation:

When an object is forced to vibrate at its natural frequency, resonance occurs. In this case, the violin string's vibrations (at a frequency that matches the wooden portion's natural frequency) and the repeated bow - pulling (applying a periodic force) lead to resonance. Resonance is the phenomenon where the amplitude of vibrations increases significantly when the driving frequency matches the natural frequency of the system.

Answer:

resonance