other positions where they are out of phase and their amplitudes (partially or fully) cancel. This is called an interference pattern. Polarization The phenomenon of polarization arises when wave motion can occur simultaneously in two orthogonal directions. Transverse waves can be polarized, for instance. When polarization is used as a descriptor without qualification, it usually refers to the special, simple case of linear polarization. A transverse wave is linearly polarized if it oscillates in only one direction or plane. In the case of linear polarization, it is often useful to add the relative orientation of that plane, perpendicular to the direction of travel, in which the oscillation occurs, such as "horizontal" for instance, if the plane of polarization is parallel to the ground. Electromagnetic waves propagating in free space, for instance, are transverse; they can be polarized by the use of a polarizing filter. Longitudinal waves, such as sound waves, do not exhibit polarization. For these waves there is only one direction of oscillation, that is, along the direction of travel. Dispersion A wave undergoes dispersion when either the phase velocity or the group velocity depends on the wave frequency. Dispersion is most easily seen by letting white light pass through a prism, the result of which is to produce the spectrum of colors of the rainbow. Isaac Newton performed experiments with light and prisms, presenting his findings in the Opticks (1704) that white light consists of several colors and that these colors cannot be decomposed any further. Mechanical waves Waves on strings The speed of a transverse wave traveling along a vibrating string (v) is directly proportional to the square root of the tension of the string (T) over the linear mass density (μ): where the linear density μ is the mass per unit length of the string. Acoustic waves Acoustic or sound waves travel at speed given by or the square root of the adiabatic bulk modulus divided by the ambient fluid density (see speed of sound). Water waves Ripples on the surface of a pond are actually a combination of transverse and longitudinal waves; therefore, the points on the surface follow orbital paths. Sound – a mechanical wave that propagates through gases, liquids, solids and plasmas; Inertial waves, which occur in rotating fluids and are restored by the Coriolis effect; Ocean surface waves, which are perturbations that propagate through water. Seismic waves Seismic waves are waves of