Mechanical waves displace their medium in a direction perpendicular to the direction the wave travels. This is called transverse wave.

Think of a rope:

* When you shake it up and down, the wave travels horizontally, but the rope itself moves vertically (up and down).

Here's an example:

* Light: Light is a transverse wave, and its medium is the electromagnetic field. The oscillations of the field are perpendicular to the direction the light travels.

Another type of mechanical wave displaces its medium parallel to the direction the wave travels. This is called a longitudinal wave.

Think of a spring:

* When you push and pull one end of the spring, the wave travels along the spring, and the coils of the spring move back and forth in the same direction as the wave.

Here's an example:

* Sound: Sound is a longitudinal wave, and its medium is air. The molecules of air vibrate back and forth in the same direction as the sound wave travels.