When a sound wave travels through matter, both its frequency and amplitude can be changed in various ways. Here are some examples:
Doppler Effect: The Doppler effect occurs when there is relative motion between the source of the sound wave, the observer, or both. If the source of the sound wave or the observer is moving toward each other, the observed frequency increases (higher pitch), and if they are moving away from each other, the observed frequency decreases (lower pitch). The amplitude of the sound wave remains unaffected by the Doppler effect.
Reflection: When a sound wave reflects off a surface, such as a wall or a solid object, its frequency remains unchanged. However, the amplitude of the reflected sound wave can be affected by factors like the nature of the surface and the angle of incidence. Reflection can result in the reinforcement or cancellation of the sound wave, leading to variations in amplitude.
Absorption: When a sound wave passes through a medium, it can be absorbed by the material. Absorption typically affects the amplitude of the sound wave, causing it to decrease as it travels through the medium. The absorption characteristics vary with different materials and frequencies. Some materials absorb certain frequencies more readily than others.
Refraction: Refraction occurs when a sound wave passes from one medium to another with different properties, such as density or temperature. As the wave enters the new medium, its speed changes, which can result in a change in direction. This change in direction can lead to a change in the perceived frequency of the sound wave. The amplitude of the sound wave generally remains unchanged during refraction.
Resonance: When a sound wave encounters a resonant object or structure, such as a musical instrument or a resonating cavity, it can lead to an amplification of certain frequencies. This amplification results in an increase in the amplitude of the sound wave at those resonant frequencies while leaving others relatively unaffected.
It's important to note that while the examples mentioned above illustrate how the frequency and amplitude of sound waves can be changed, they are subject to the properties of the medium through which the sound wave propagates. The behavior of sound waves in different materials can be complex, and factors such as density, temperature, and composition can influence the specific changes observed in frequency and amplitude.