Of couse, sound waves change depending on the material that sound travels through. Most people hear sounds when they travel through the air. But sound waves can travel through ang any medium. Sound waves can travel through solids, through liquids and through gases. But sound cannot travel through a vacuum like outer space. In space, there is no sound. When sound waves travel through air, the sound waves are actually vibrating. The waves travel in the direction of where the waves are going. This vibration pushes the air, which is "the sound" we eventually hear. The vibration can be caused by manythings. Maybe a loud speaker in a stereo system causes the sound to vibrate. It could be the sound of a car engine starting up or a person speaking. When a person speaks, their vocal chords in their throat vibrate. All these sources emit sound waves.