What property is necessary for sound waves to travel?

Sound waves require a medium to travel, which can be a solid, liquid, or gas. This is because sound is a mechanical wave, meaning it propagates through vibrations of particles in a substance. When sound waves move, they create compressions and rarefactions in the medium, enabling the energy to be transmitted from one particle to another. Without a medium, such as in a vacuum where no particles exist to transmit the vibrations, sound cannot travel.

The other options, while relevant to different types of waves or physical phenomena, do not serve as necessary conditions for the propagation of sound. A vacuum, for example, is a space devoid of matter, making it impossible for sound waves to travel. Similarly, while an electric field may influence electromagnetic waves, it does not facilitate the movement of sound waves. Pressure differences are involved in the mechanics of sound propagation, but they arise as a consequence of sound waves traveling through a medium, rather than being a separate requirement for sound to exist. Thus, having a medium is essential and is the correct answer.