Longitudinal wave and seismic P-waves (created by earthquakes and explosions). In longitudinal waves, the displacement of the medium is parallel to the propagation of the wave, and waves can be either straight or round. A wave along the length of a stretched Slinky toy, where the distance between coils increases and decreases, is a good visualization. In the case of longitudinal harmonic sound waves, the frequency and wavelength can be described by the formula where: The quantity "x"/"c" is the time that the wave takes to travel the distance "x". The ordinary frequency ("f") of the wave is given by The wavelength
What Is History? to suit their facts, and takes part in a dialogue between past and present. Summing up his argument, Carr puts forward his own answer to the question of "what is history?", remarking that "it is a continuous process of interaction between the historian and his facts, an unending dialogue between the past and the present." it is precisely for matters of this kind that the historian is entitled to rely on what have been called the auxiliary sciences of history In his second chapter, Carr focuses on the influence that society plays on forming the approach of the historian and