Where dose sound come from and how is it made and where can you not here sound

the sound comes from particles moving from a state of rest and forced out like talking, your vocals would be is their resting state when you start talking making pressure by the movement to force them out to air. since sound is a movement of particles it can only move where there are particles, the less dense the particles are the easier for the sound to move. you can not hear sound in vacuums, where there are no particles. You can not hear voices from behind thick walls, inside a room that is entirely closed.

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explanation:

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equal area projections

equal-area projection. a projection in which regions on the earth's surface that are of equal area are represented as equal.