Children are introduced to the physics of sound. Energy causes air molecules to move slightly back and forth. The energy is passed from molecule to molecule, causing a longitudinal sound wave. The more energy used, the bigger the longitudinal wave and the louder the sound. The ear contains a thin flexible part, the tympanic membrane, that picks up the motion of the molecules in the sound wave. Sound waves can travel through other materials in addition to air. Sound travels faster through materials with tightly packed molecules. Some examples are given. Atoms, molecules, energy, and longitudinal waves are defined. Students are invited to try a simple experiment. 24 full-color, illustrated pages. Reading Level 1-3, Interest Level 2-5. Includes a pronunciation guide for scientific terms.