What happens to sound waves as they move away from the source?

As sound waves move away from their source, the phenomenon that occurs is a decrease in amplitude. Amplitude is the measure of the wave's maximum displacement from its rest position and is directly related to the perceived loudness of the sound. As sound waves travel through a medium, they lose energy due to factors such as absorption and scattering, especially in a non-ideal environment. This loss of energy manifests as a reduction in amplitude, making the sound quieter as it moves farther from the source.

The other options explore different properties of sound waves but do not accurately represent what happens as the waves propagate away from the source. Frequency typically remains constant for a given source unless the wave experiences the Doppler effect due to relative motion between the source and observer. Wavelength is connected to both speed and frequency, and since the speed of sound in a medium typically remains constant under stable conditions, the wavelength does not inherently decrease as the sound moves away. Lastly, the speed of sound is determined by the medium through which it travels and does not increase simply because the waves are moving away from the source. Therefore, the correct response focuses on the decrease in amplitude as sound waves travel outward.