What term describes a wave in which the vibration is parallel to the direction the wave travels?

• A. Longitudinal Wave
• B. Transverse Wave
• C. Medium
• D. Density

Answer: (A)

Longitudinal waves are waves in which the vibration of the medium is parallel to the direction of travel. In these waves, the particles move back and forth along the same line that the wave moves, creating compressions where particles are pushed close together and rarefactions where they are spread apart. This is why energy can pass through the medium even though the individual particles aren’t moving along the wave’s path. A familiar example is sound moving through air. By contrast, a transverse wave has particle motion perpendicular to the direction of travel—for instance, a rope or string moving up and down while the wave propagates horizontally. Density, meanwhile, is a property of the material, not a type of wave.