1) Sound is produced by vibrations traveling through a medium such as air, which can be heard when they reach the ear. Most sounds are produced by vibrating objects like strings, reeds, or vocal cords. 2) Sound travels faster in solids and liquids than in gases, and the speed of sound in air increases with rising temperature. Reflection and refraction can cause sounds to bend or echo. 3) Interference occurs when waves meet and either constructively or destructively interfere with each other, and resonance amplifies vibrations matching an object's natural frequency.