What characteristic of sound is defined by the amplitude of the vibration?

The characteristic of sound defined by the amplitude of the vibration is loudness. Amplitude refers to the height of the sound wave; greater amplitude results in a louder sound, while smaller amplitude corresponds to softer sounds. This relationship stems from the physics of sound waves, where the amplitude of the wave reflects how much energy is being transferred through the medium, influencing our perception of volume.

Pitch, on the other hand, is primarily determined by the frequency of the sound wave, which is the number of vibrations per second. Frequency affects how high or low a sound appears to us but does not relate to how loud or soft it is. Speed refers to how fast sound travels through a medium, which is influenced by factors like temperature and density, rather than the characteristics of the sound wave itself.