Sound is produced when an object vibrates. When something vibrates, it transfers kinetic energy to the molecules of the medium surrounding it. This kinetic energy causes the molecules in the medium to vibrate, transferring kinetic energy to new molecules. This transfer of kinetic energy through a medium causes a series of compressions (areas where the molecules are crowded together) and rarefactions (areas where the molecules are spread out). These compressions and rarefactions move through the medium, away from the original vibration. When a series of compressions and rarefactions move through a medium, it is called a longitudinal wave. Therefore, sound is a longitudinal wave.

When you speak, air moves from your lungs past your vocal cords, causing them to vibrate. Your vocal cords consist of two flaps of tissue that can move closer to or farther away from each other. When they move closer together, they cause a...