What causes sound waves to differ in intensity?

Sound waves differ in intensity primarily due to their amplitude. Amplitude refers to the maximum displacement of particles in the medium through which the sound waves travel. When the amplitude is larger, more energy is transferred through the medium, resulting in a louder sound. Conversely, a smaller amplitude means less energy and, therefore, a quieter sound.

Factors like frequency and wavelength do play a role in sound characteristics, but they do not directly determine intensity. Frequency relates to the pitch of the sound, while wavelength is the distance between successive peaks of the sound wave. Speed is determined by the medium and does not inherently affect the intensity of the sound. Therefore, amplitude is the key factor that directly influences how intense or loud a sound wave is perceived.