Mechanical waves are waves that require a medium to propagate. They involve the physical movement or vibration of particles in a medium. Transverse waves are a type of mechanical wave in which the particles of the medium vibrate perpendicular to the direction of the wave's propagation. In other words, the particles move up and down or sideways, rather than back and forth in the direction the wave is traveling. Examples of transverse waves include water waves, electromagnetic waves such as light and radio waves, and vibrations on a string.