Question

why do sound need a medium to travel?

Answer 1

Sound waves are transmitted as vibrations in the particles. Hence sound need a medium to travel as in vaccum no particles are present.

Answer 2

That's because sound is a mechanical wave. ... In contrast, electromagnetic waves require no medium, but can still travelthrough one. Since a vacuum is defined as lacking a medium, thensound and correspondingly, mechanical waves, cannot propagate through a vacuum. This is why we can't hear voices or sounds in space.