Question

what does sound need in order to propagate (move)? what happens to sound as molecules get more dense or closer together?

Explanation:

1. For the first part: Sound is a mechanical wave, and mechanical waves require a medium (like solid, liquid, gas) to propagate because sound travels by vibrating particles in the medium.
2. For the second part: When molecules are more dense or closer together (e.g., in solids compared to gases), the sound waves can transfer energy more efficiently between particles, so the speed of sound generally increases (since the time between particle collisions for energy transfer is reduced).

Answer:

1. Sound needs a medium (solid, liquid, or gas) to propagate.
2. As molecules get more dense or closer together, the speed of sound generally increases (because energy transfer between vibrating particles is more efficient in a denser medium with closer - packed molecules).