In this section, we will examine the structure of mechanical waves, both transverse and longitudinal. More specifically, we will learn about some of the different parts and properties of these waves.
Transverse Waves
A transverse wave is a wave in which the particles of the medium are displaced in a direction perpendicular to the direction of energy transport. A transverse wave can be created in a rope if the rope is stretched out horizontally and the end is vibrated up-and-down. If a snapshot of the resulting wave could be taken so as to freeze the shape of the rope in time, then it would look like the following graph.
The vertical axis is the amplitude of the wave while the horizontal axis can be either distance or time.
The highest point on the graph of the wave is called the crest and the lowest point is called the trough.
The line through the center of the wave is the resting position of the medium if there was no wave passing through.
The amplitude of a wave is a measure of the displacement of the wave from its resting position. The amplitude is a measure of the strength or intensity of the wave. For example, when looking at a sound wave, the amplitude will measure the loudness of the sound. The energy of the wave also varies in direct proportion to the amplitude of the wave.
The wavelength (λ) of a wave is the length of one complete cycle of a wave
and corresponds to the distance between two corresponding points on back-to-back cycles of a wave. This can be measured between two crests of a wave or two troughs of a wave.
The frequency (f) is the number of occurrences of a repeating event per unit of time. The frequency of a wave is therefore the number of wave crests (or troughs) that pass by a fixed location in a given amount of time. Frequency is measured in Hertz, or cycles per second.
The period (T) is the duration of time of one cycle in a repeating event. The period of the wave is measured as the time between wave crests, i.e., the time it takes a wave to travel the wavelength. The period is measured in time units (seconds).
The period and frequency are closely related to each other. They are reciprocals of each other as shown in the following formulas: