Question

sound waves belong to a group called mechanical waves - specifically, longitudinal waves. this means they need a material, called a medium, to travel through - unlike light waves that can travel through empty space. sound waves involve compressions, where particles are pressed together, and rarefactions, where they spread out. the speed of sound changes depending on the material it travels through. it moves fastest through solids because the particles are packed closely together, making it easier for the energy to pass through. liquids come next, and sound waves move slowest through gases due to the spaced - out particles. choose the correct answer. what do sound waves need to travel through? a vacuum a medium neither

Explanation:

The text states that sound waves need a material (a medium) to travel through, unlike light waves that can travel through empty space (a vacuum).

Answer:

B. a medium