How does sound get through objects, through the air, to your ears?
Well, sound is a form of energy that travels through materials by making PARTICLES in the materials vibrate.
When the particles are packed together tightly (makes the material DENSE), the sound waves travel easily and quickly.
In materials where the particles are spread far apart, for example, gases at room temperature, the sound waves do not travel as quickly.
Got that? Maybe read it again and see if that helps you with the following questions.