“Playing with Physics” apps allow interactive simulation of select physics phenomena.

The “Huygens’ Principle” makes it possible to represent waves in an isotropic environment, i.e. in an environment in which the waves propagate in all directions at the same speed. Waves are represented by wavefronts and rays. Wavefronts have a spherical shape and are considered to be flat at a large distance from the wave source. Rays as perpendicular to the wavefront show the direction of wave propagation at a given point.