Light and electromagnetic waves are also transverse waves, however they are self-propagating, meaning that they sustain themselves due to the magnetic field they create, and thus can travel through a vacuum, only slowing down slightly when passing through water or air.

Examples of transverse waves include vibrations on a string and ripples on the surface of water. We can make a horizontal transverse wave by moving the slinky vertically up and down. In a longitudinal wave the particles are displaced parallel to the direction the wave travels.

For transverse waves the displacement of the medium is perpendicular to the direction of propagation of the wave. Transverse waves cannot propagate in a gas or a liquid because there is no mechanism for driving motion perpendicular to the propagation of the wave.

Figure 1: Diagram of the directions of propagation and displacement for three types of wave: (a) longitudinal, (b) transverse (unpolarised), and (c) transverse (polarised). Electromagnetic waves are transverse, and can be polarised.

The reason that only transverse waves can be polarised is that their vibrations can potentially occur in all directions perpendicular to the direction of travel. It is therefore possible to confine the vibrations to a single plane.

All waves exhibit similar properties, and both light and sound are types of waves (although, technically, light is a transverse wave and sound is a longitudinal wave). One feature of waves, known as diffraction, is that they can bend around corners or obstacles.

Ultrasonic waves are high-frequency sound waves. The frequency of sound waves is greater than 20kHz. These waves are longitudinal in nature, hence it cannot be polarized.

No, water waves cannot be polarized because they are longitudinal waves. Longitudinal waves cannot be polarized because the direction and the propagation of waves are in the same direction.