longitudinal
Waves may be transverse, longitudinal, or a combination of the two. Water waves are actually a combination of transverse and longitudinal. The simplified water wave illustrated in Figure 16.30 shows no longitudinal motion of the bird. The waves on the strings of musical instruments are transverseso are electromagnetic waves, such as visible light. Sound waves in air and water are longitudinal. Their disturbances are periodic variations in pressure that are transmitted in fluids. Fluids do not have appreciable shear strength, and thus the sound waves in them must be longitudinal or compressional. Sound in solids can be both longitudinal and transverse.