Final answer:
The amplitude of a waveform is the characteristic that corresponds to volume changes over time, affecting the sound's loudness.
Step-by-step explanation:
The characteristic of a waveform that deals with volume changes over time is the amplitude of the wave. In the context of sound waves, amplitude relates to the loudness or volume. When a waveform is graphed, the amplitude is the height of the wave peaks above or below the baseline.
The greater the amplitude, the louder the sound is perceived, assuming the waveform represents a sound wave. Changes in volume thus lead to changes in amplitude on the waveform's graphical representation. However, the frequency and period of the wave, which affect pitch and rhythm, remain essentially unchanged with volume adjustments.