Mechanical waves require a medium.

• A. They travel through empty space with no medium.
• B. They require a medium to travel.
• C. They are only sound waves.
• D. They do not carry energy.

Answer: (B)

Mechanical waves propagate only when there is a material through which they can transfer energy. The wave is a disturbance that makes particles in the medium vibrate and pass that disturbance along to neighboring particles, so energy moves through the medium even though the medium itself may not travel with the wave. In a vacuum, there are no particles to interact, so mechanical waves cannot propagate.

That’s why the statement that they require a medium to travel is the best answer. The other ideas don’t fit: mechanical waves do not travel through empty space, they are not limited to sound waves (they include water waves and seismic waves), and they do carry energy.