It's not quite true that sound waves can only travel through air. While air is a common medium for sound, sound waves can also travel through other mediums, including:

* Liquids: Think of how you hear sounds underwater. Water is a very effective medium for transmitting sound.

* Solids: You can hear sounds transmitted through solids like wood, metal, and even your own bones!

* Gases: While air is the most common gas, sound can travel through other gases like helium or carbon dioxide.

What's important is that the medium has molecules close enough together to vibrate and pass on the sound energy.

Why sound can't travel in a vacuum:

The only place sound can't travel is a vacuum, which is an empty space with no molecules. Since there's nothing to vibrate, the sound energy has no way to propagate.