What is sound?
Sound is made when an object vibrates. If we stretch a rubber band and let go, it vibrates and makes a sound. The faster an object vibrates the higher the sound: a mosquito beats its wings hundreds of times a second, so its sound is thin and high; a beetle or bee sounds lower. The bigger the vibration, the louder the sound. Sound is passed along a chain of tiny particles in the air, so sound does not travel in airless space. Sound also travels through water and solids. Sound is drawn as a wave: a tall wave means a loud sound, and frequent waves mean a high sound. The human ear hears sounds of about 20 to 20,000 vibrations per second.
Rubber band experiment: hold a band in both hands, pluck it gently and sharply; when is the sound higher? Then whisper and say a riddle loudly and see who hears it in different corners of the class.