How does sound move?

Sound needs a medium like air, water or
solids to travel through. When something
moves through the air, it disturbs the
molecules of gas in the air around it. The air
vibrates or moves back and forth. This
vibration is heard as sound. The greater the
vibration, the louder the sound. Since sound
travels in waves, it gets weaker the further it
travels. That is why your voice cannot be
heard beyond a certain distance. If you put in
more energy and shout, the sound waves will
be stronger and travel further so that your
voice can be heard further. Sound cannot
travel through a vacuum, because a vacuum
is completely empty, and has no medium
with which to carry the sound wave.