Final answer:
The amplitude of sound waves determines the loudness of sounds, with larger amplitudes producing louder sounds, measured in decibels.
Step-by-step explanation:
The loudness of sounds is determined by the amplitude of sound waves. When you speak more loudly, the amplitude of the sound waves increases. This means that the waves have larger peaks and troughs, indicating more energetic vibrations, which results in a louder sound as perceived by our ears. The loudness or volume of sound is commonly measured in decibels (dB), and our perception of volume is not only influenced by amplitude, but also by the frequency of the sound, as the human ear has varying sensitivity to different frequencies.