# Properties of Waves

A *wave* can be defined as the transfer of energy between two points without any physical transfer of matter. Waves on the surface of the sea or on a lake provide an obvious example, because they are highly visible. The fact that they transfer energy can be seen from the effects of coastal erosion over many years, and from the more immediate effects involving the transfer of materials onto the shoreline. Sound is an example of waves that we can hear, and is caused by vibrating air molecules. A basic sine wave is illustrated below.

A typical sine wave

The properties of waves that can be measured or calculated are:

*Amplitude*- the height of the wave in meters*Wavelength*- the distance between consecutive peaks in meters*Period*- the time a wave takes to pass a given point in seconds*Frequency*- the number of waves that pass a point in one second*Speed*- the speed at which a wave propagates in meters per second

The symbol normally used to denote wavelength is the Greek letter λ (lambda). Wavelength is commonly expressed in terms of its frequency (ƒ) and velocity of propagation (*v*), as follows:

Frequency (ƒ) is the term used to describe the number of oscillations (cycles) per second of a wave. The unit of frequency is the *Hertz* (Hz), and one Hertz is equal to one cycle per second. The term is named after the German physicist *Heinrich Rudolph Hertz*, who first produced and observed electromagnetic waves in 1887. The term is combined with metric prefixes to denote multiple units such as the *kilohertz* (10^{3} Hz), *megahertz* (10^{6} Hz), and *gigahertz* (10^{9} Hz). Other properties of waves can be calculated:

*Period*= frequency^{-1}*Speed*= wavelength / period (or wavelength x frequency)