What makes the bottles make different sounds?

The different sounds that bottles make when struck are due to the air and liquid inside. When you hit a bottle with something, it compresses the air inside the bottle. This compressed air then moves the water molecules around, causing them to vibrate. The rate at which the molecules vibrate determines the musical note that is played. Bottles filled with the same amount of water make the same note, while different amounts of water, or bottles with different shapes, will make different notes.