They can travel through a vacuum.
Explanation
Sound is a form of energy produced by vibrating bodies. It propagates as a mechanical wave, which fundamentally requires a material medium (solid, liquid, or gas) for transmission and cannot exist in the absence of matter.
Statement-wise Analysis:
- Statement They are mechanical waves. is Correct: Sound waves are classified as mechanical waves because they rely on the oscillation of material particles to transfer energy. They cannot generate or propagate without a physical medium.
- Statement They can travel through a vacuum. is Incorrect: Sound waves cannot travel through a vacuum. In a vacuum, there are no molecules or particles to vibrate and transmit the wave energy. This stands in contrast to electromagnetic waves (such as light), which can propagate through a vacuum.
- Statement They propagate as longitudinal waves in air. is Correct: In fluids like air, sound propagates as a longitudinal wave. The particles of the medium oscillate parallel to the direction of wave propagation, creating alternating regions of high pressure (compressions) and low pressure (rarefactions).
- Statement They transport energy, not matter. is Correct: A fundamental property of wave motion is that it transports energy and momentum from one location to another without the bulk transport of matter. The particles of the medium merely vibrate around their mean positions.
Key Takeaway:
Sound is a mechanical, longitudinal wave that necessitates a material medium for propagation; it is physically impossible for sound to travel through a vacuum.