Question

How does an unamplified guitar produce sounds so much more intense than those of a plucked string held taut by a simple stick?

Short answer

The sound from the strings of a guitar resonates in the soundbox of the guitar, that’s why the sound is more intense.

Step-by-step solution

Physics of guitar

The sound produced by the strings of the guitar first enters the soundbox of the guitar. This soundbox is designed to produce resonance, because of which the intensity of sound increases.

sounds of a plucked string held taut by a simple stick

A plucked string that is held taut by a simple stick produces the same sound, but due to the absence of a soundbox, it does not get amplified.

Conclusion

strings of a guitar are set to resonate, to produce intense sound whereas strings of a simple stick cannot resonate.