When waves encounter new mediums, barriers, or other waves they can behave in different ways. In physics these behaviors are described using some of the terms below.
The word "reflection" is used in everyday life to describe what we see in a mirror or on the surface of the water. In physics, a reflection is when a wave encounters a new medium that acts as a barrier, causing the wave to return to the original medium. The wave "reflects" off the barrier at an angle that is incident to the angle of the wave hitting the barrier (see below).
Refraction of a wave occurs when a wave changes direction upon moving from one medium to another. Along with the change of direction, refraction also causes a change in the wavelength and the speed of the wave. The amount of change in the wave due to refraction is dependent on the refractive index of the mediums.
One example of refraction is a prism. When white light enters the prism, the different wavelengths of light are refracted. The different wavelengths of light are each refracted differently and the light is split into a spectrum of colors.
Diffraction occurs when a wave stays in the same medium, but bends around an obstacle. This can occur when the wave encounters a small object in its path or when the wave is forced through a small opening. An example of diffraction is when a water wave hits a boat and bends around the boat. The waves after the boat are changed or diffracted.
An example of a diffracted wave passing through a small opening.
Polarization is when a wave oscillates in one particular direction. Light waves are often polarized using a polarizing filter. Only transverse waves can be polarized. Longitudinal waves, such as sound, cannot be polarized because they always travel in the same direction of the wave.
In this picture the unpolarized light wave travels through the filter and then is polarized along a single plane.
Absorption is when a wave comes into contact with a medium and causes the medium's molecules to vibrate and move. This vibration absorbs or takes some of the energy away from the wave and less of the energy is reflected.
One example of absorption is black pavement which absorbs energy from light. The black pavement becomes hot from absorbing the light waves and little of the light is reflected making the pavement appear black. A white stripe painted on the pavement will reflect more of the light and absorb less. As a result the white stripe will be less hot.
When one wave comes into contact with another wave this is called interference. When the waves meet the resulting wave will have the amplitude of the sum of the two interfering waves.
Depending on the phase of the waves the interference can be constructive or destructive. If the resulting wave has a higher amplitude than the interfering waves, this is constructive interference. If it has a lower amplitude, this is called destructive interference.