Second sound

Second sound is the sound waves that are produced when an object is vibrating. This sound is made up of two parts: the first sound, which is the original sound that started the vibration, and the second sound, which is caused by the object's vibration. The second sound is usually quieter than the first sound and can often be heard in the air around us. For example, when you hear a guitar playing, the first sound is the notes played by the guitar, and the second sound is caused by the vibrations of the strings and body of the guitar.