PS-7.2   Compare the nature and properties of transverse and longitudinal/compressional mechanical waves.
Key Concepts
Mechanical waves: transverse waves, longitudinal or compressional waves
Wave properties: crest, trough, compression, rarefaction
We have already learned that there are two types of waves, electromagnetic waves and mechanical waves. Here we will look at the characteristics of mechanical waves.
Mechanical transverse waves consist of an alternating series of wave crests and troughs as illustrated in diagram "A".
Diagram A    
    In transverse mechanical waves wavelength is defined as the distance between any two consecutive like points such as between points X and Y in the diagram above. However, for clarity, we can consider wavelength to be simply the distance, measured in meters, from the crest of one wave to the crest of the next wave.
    Longitudinal compression waves consist of alternating areas of compression and rarefaction. The wavelength of a longitudinal wave is the distance between areas of maximum compression as shown below in diagram "B". The dark areas are areas where the molecules of the medium are squeezed or compressed together. The lighter bands are areas of rarefaction, that is, areas where the molecules of the medium are pulled further apart from each other. Areas of compression are areas of high pressure and areas of rarefaction are areas of lower pressure.
Diagram B            
    Some waves cannot be classified as either longitudinal of transverse waves. For example, a water wave has characteristics of both transverse AND longitudinal waves. In water waves the vibration or particle motion is circular. Look at this website and compare the particle motion in longitudinal, transverse, and water waves.